1. R3 Controls, Valves, Accessories & Heat Pumps
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
R3 Controls, Valves, Accessories & Heat Pumps
#1 Controls
© 2004 Refrigeration Training Services
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2. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Pressure Controls
9/16/2018
Stop and Start current flow
Energize or de-energize refrigeration components
Typical pressure controls:
Low Pressure – Closes on rise
High Pressure – Opens on rise
Low Ambient fan control – Closes on rise
Oil Safety Switch – Opens on rise in differential
- Has a time delay
Pressure switches are used to stop and start electrical current flow to refrigeration components.
When working with refrigeration controls the word energize means to apply electricity to an electrical component. The word de-energize means to shut off the electricity to a component.
Contacts must be closed to allow current flow to energize a device.
The most common switches and contact positions are:
Low pressure switch – closes on a rise in pressure.
High pressure switch – opens on a rise in pressure.
Low ambient control – closes on a rise in pressure.
Oil safety switch – opens on a rise in the differential of oil pump pressure to suction pressure.
The oil safety switch has a time delay before it shuts off the compressor.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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3. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Low Pressure Control
When pressure falls, circuit opens.
Adjusting the control shown on the next slide:
Set the cut-in pressure
Set the differential
The cut-out is the cut-in pressure minus the differential.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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4. Picture of Ranco LP control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Picture of Ranco LP control
Low Pressure Control
Differential
Cut-in
Example:
Cut-in 50 psig
Diff. (-)20 psig
Cut-out 30 psig
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

5. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Low Pressure Control
The next control is easier to set:
Set the cut-in pressure
Set the cut-out pressure
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

6. Picture of Johnson Controls LP
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Low Pressure Control
9/16/2018
Picture of Johnson Controls LP
Cut-in
Cut-out
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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7. System Low Pressure Normal Operation
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
System Low Pressure Normal Operation
Following slide, walk-in refrigerator:
Tstat drops 5° before shutting off
Coil temperature drops also
Coil temperature is 10° below box temperature
(Because walk-in evaporator TD is 10°)
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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8. Normal Cycle for a 35° Walk-in Refrigerator
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Normal Cycle for a 35° Walk-in Refrigerator
R22
Pressure
10º TD Evaporator Coil
Temp
35º
Tstat Cut-in
35º
62#
Box Temp
5º Drop
Evaporator
Operating Range
Evaporator Temp
30º
Tstat Cut-out
42#
30º
20º
10º TD
20º
Coil Temperature
Refrigerating Cycle
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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9. Low Pressure Control for Safety
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Low Pressure Control for Safety
9/16/2018
Protects compressor due to loss of refrigerant
Indoor condensing unit LP control cut-out:
20° below coil temperature when tstat is satisfied
Cut-in is affected by ambient
Outdoor units, cut-in equal to winter design
Walk-in refrigerator example:
Normal winter design temperature is +10°
Cut-in should be 10 to 20 psig above cut-out
Or 30° below coil temperature when tstat shuts off
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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10. Coil temp at tstat cut-out
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Low Pressure Control
9/16/2018
As a Safety control
35º Walk-in Refrigerator (Indoor condensing unit)
R22
Pressure
Temp
35º
Tstat Cut-In
62#
35º
Evaporator Temp
Evaporator
Operating Range
Evaporator Temp
20º
Coil temp at tstat cut-out
42#
20º
Coil temperature drops
due to lack of refrigerant
This slide is an example of using a low pressure control as a safety control on a walk-in refrigerator with condensing unit located indoors.
On a walk-in refrigerator the evaporator TD or temperature difference between box temperature and evaporator temperature is about 10°. In a 35 ° walk-in the box temperature can drop down to 30° before the thermostat is satisfied. Therefore, the evaporator temperature would come down to about 20° (30° - 10°) or 42# on an R22 system.
When used as a safety the control cut-out should be the pressure equivalent to about 20° below that, or 0° (20° – 20°) or 24# CO.
24# 0º
Indoor LP control 0º
(20º below lowest evap temp) 0#
-50º
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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11. LP Control on Outdoor Units
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
LP Control on Outdoor Units
Cut-out is 20° below cut-in
Cut-in is affected by outdoor ambient:
Cut-in should be equal to “winter design”
Following slide example:
Walk-in refrigerator located in Washington, DC
Normal winter design temperature is +10°
LP control cut-in set at +10°
LP control cut-out is 20° lower, or -10°
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
No reproduction or unauthorized use allowed

12. Coil temp at tstat cut-out
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Low Pressure Control
9/16/2018
As a Safety control
35º Walk-in Refrigerator, Outdoor Unit
(Washington, DC winter design +10° F)
R22
Pressure
Temp
35º
Tstat Cut-In
62#
35º
Evaporator Temp
Evaporator
Operating Range
Evaporator Temp
20º
Coil temp at tstat cut-out
42#
20º
LP control +10°
Normal winter design temp
This slide is an example of using a low pressure control as a safety control on a walk-in refrigerator with an outdoor unit near Washington, DC.
On a walk-in refrigerator the evaporator TD or temperature difference between box temperature and evaporator temperature is about 10°. In a 35 ° walk-in the box temperature can drop down to 30° before the thermostat is satisfied. Therefore, the evaporator temperature would come down to about 20° (30° - 10°) or 42# on an R22 system.
On outdoor units the determining factor is the cut-in pressure. The example above is for a unit in or near Washington, DC where the winter “design” (the average lowest winter temperature) is +10. Since ambient conditions below this would prevent the control from cutting in, that is the minimum cut-in we want.
The cut-in (CI) should be a differential of about 20# from cut-out. If the normal winter ambient is below +10 an outdoor unit may have to be set at a lower cut-in setting.
If the CO is 17# and the differential 20# the CI would be 37# (17# + 20#). This is well below the highest normal operating pressure of 62# which is the thermostat CI at 35°.
A “Rule-of-Thumb” for setting LP controls for safety is (at ambient of +10):
Medium temperature Applications: Cut-out at a pressure equal to -10°.
Low temperature applications: Cut-out at a pressure equal to -40°.
33#
10º
17#
-10º
Outdoor LP control -10°
(20 ° below cut-in) 0#
-50°
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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13. Low Pressure Control Used as a Thermostat
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Low Pressure Control Used as a Thermostat
Thermostats sense box temperature
LP Control senses pressure
Pressure equals evaporator temperature
LP Control is both a temperature and safety control:
Cut-in:
At a pressure equal to the maximum box temperature
Cut-out:
At a pressure equal to 5° below maximum box temperature,
Less the coil TD
Less 2 ° (Allowance for coil pressure drop)
A thermostat measures the air temperature in a box. The low pressure control measures the pressure, which is directly related to the evaporator temperature.
A low pressure control can be used as a temperature control without losing its benefit as a safety control. The control still cuts-out on pressure, whether it is because the box is cold enough, or because the refrigerant has leaked out.
The control cut-in is at a suction line pressure equivalent to the maximum temperature of the box.
For instance, if the refrigerator is to maintain at least a 38° space temperature the control should cut-in the compressor when the refrigerant temperature inside the evaporator equals the space temperature of 38°.
The compressor will run until the temperature in the box is about 5° below where it started, just like a thermostat. However, it is doing this by sensing the suction pressure based on the TD or temperature difference design of whichever evaporator is being used.
Most reach-in refrigerators have a TD of between 15° to 20°. This means that the temperature of the refrigerant inside the evaporator is 15 ° or 20 ° below the temperature of the air in the box that is blowing throw the evaporator.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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14. Low Pressure Control As a Temperature Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Reach-in 38º Box Temperature
Using a 20º TD Evaporator Coil
With a TEV
Box Temp
66#
38º
After the compressor starts the box temperature begins to drop
63#
36º
Evaporator Temp
The evaporator temperature also drops, but 20° lower than the box
39#
16º
This graph and the next three slides represents how both the box temperature and the evaporator temperature fall and rise over one complete cycle. We are using a medium temperature reach-in refrigerator with a 20° TD evaporator.
The pressures represent R22 and show the cut-in and cut-out if the low pressure (LP) control is used as a temperature control. However, they would be the same if we used a Tstat that had a 5° differential. Using an LP control allows the coil to defrost before it will come on.
The pressures would be different if the refrigerant used was R134a, or R404, but the coil temperatures remain the same.
Whether it is a thermostat or a low pressure control it will cut in the compressor when the box temperature gets up to 38°. The box temperature comes down gradually, but the evaporator temperature quickly drops to about 20° below the box temperature (20° TD).
Compressor On
Cut In
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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15. Low Pressure Control As a Temperature Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Low Pressure Control As a Temperature Control
9/16/2018
Reach-in 38º Box Temperature
Using a 20 º TD Evaporator Coil
With a TEV
R22
Pressure
Temp
Box Temp
66#
38º
60#
34º
Pressure and temperature continue to drop
Evaporator Temp
The box and evaporator temperatures continue to fall
37#
14º
Cut In 66# = 38º
Compressor On
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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16. Low Pressure Control As a Temperature Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Low Pressure Control As a Temperature Control
9/16/2018
Reach-in 38º Box Temperature
Using a 20 º TD Evaporator Coil
With a TEV
R22
Pressure
Temp
66#
38º
35#
35#
38º
Box Temp 5º
Pressure and temperature fall to cut-out point
59#
33º
20º TD
Evaporator Temp
36#
13º
The box temperature is down to 33° and the suction pressure is down to 13° or 36#, the low pressure control cut-out.
The compressor shuts off.
NOTE: The actual LP control cut-out would actually be 2 psig LESS because of the pressure drop in most evaporators. This is normal for self-contained reach-ins. 2º
2 # Coil Pressure Drop
34#
11º
Cut In 38°
Cut Out 11°
Compressor On
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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17. Low Pressure Cuts Out, Now What?
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Low Pressure Cuts Out, Now What?
Pressure (and coil temperature) slowly rise
Evaporator defrosts automatically
Note: good remedy for boxes with thermostats that freeze up often
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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18. Low Pressure Control As a Temperature Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Low Pressure Control As a Temperature Control
9/16/2018
Reach-in 38º Box Temperature
Using a 20 º TD Evaporator Coil
With a TEV
R22
Pressure
Temp
66#
38º
Box Temp
Evaporator Temp
27º
11º
38º
35#
35#
38º
Box Temp
Evaporator Temp
Compressor Off Cycle
A Summary of what is happening in this and the first three slides:
This graph represents how both the box temperature and the evaporator temperature fall and rise over one complete cycle. We are using a medium temperature reach-in refrigerator with a 20° TD evaporator.
The pressures represent R22 and show the cut-in and cut-out if the low pressure (LP) control is used as a temperature control. However, they would be the same if we used a Tstat that had a 5° differential. Using an LP control allows the coil to defrost before it will come on.
The pressures would be different if the refrigerant used was R134a, or R404, but the coil temperatures remain the same.
The tstat, or pressure control, cuts-in when the box temperature gets up to 38°. The box temperature comes down gradually, but the evaporator temperature quickly drops to about 20° below the box temperature (20° TD).
The box and evaporator temperatures continue to fall until they reach the cut-out point of the tstat (38° – 5° = 33°).If we’re using an LP control it cuts out at a pressure corresponding to the coil temperature at a 33° box temperature less the 20° TD differential, or 13° (33° – 20° = 13°).
The actual LP control cut-out would be the pressure equivalent to 11° because there would a temperature drop equal to 2# for the pressure drop through the evaporator coil. This is normal on self-contained reach-ins.
After the control cycles the compressor off, the coil and box temperatures rise until they reach the cut-in point of 38°. The control cuts-in, the compressor comes on, and the cycle begins again.
34#
11º
LP Control ready to start another cycle
Cut In 38°
Cut Out 11°
Compressor On
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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19. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
High Pressure Control
Protects compressor from high head
Opens compressor circuit
High Pressure Control cut-out setting:
155° Condensing temperature, or
60° above normal maximum ambient
Example: If normal maximum ambient is 95°
Cut-out is 95°+ 60°= 155°
Equivalent pressure: 405 psig for R22
475 psig for R404A
The high pressure control stops the compressor if the head pressure is too high. The control’s switch opens, or cuts out, on a rise in pressure.
These controls are especially important on water-cooled equipment because interruption of the water supply is very likely.
Most compressors operate normally at a condensing temperature 30° above the ambient air entering the condenser. This is known as the condenser TD (temperature difference) or the “condenser split”. High efficiency condensers may only have a “condenser split” of 15° to 20°.
NOTE: Some freezer condensers operate as low as a 15° TD because the manufacturer is trying to maintain low compression ratios.
Refer to the manufacturers specifications on the proper setting of high pressure controls for the refrigerant being used.
If this information is not readily available you can use a “rule-of-thumb” of 60° above the normally highest ambient for your area.
For example, if the normal high ambient is 95° add 60° and set the control to cut out at a pressure equal to 155°. If you are using R404A that cut-out pressure would be 475#.
A manual reset control provides the best equipment protection. However, an automatic reset control will allow the compressor to run for short periods of time, providing some refrigeration until the owner notices that there is a problem with the equipment.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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20. High Pressure Control Manual Reset (After pressure drops 50 #) Cut-out
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
High Pressure Control
9/16/2018
Manual Reset
(After pressure drops 50 #)
Cut-out
Most have Auto Reset
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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21. Condensers & Low Ambients
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Condensers & Low Ambients
9/16/2018
Low ambient:
Air entering the condenser below 60°
What is the problem with low ambient?
Lowers condensing temperature,
Lowers head pressure,
Lower pressure to metering device,
Lower pressure drop across metering device,
Starves evaporator of refrigerant,
Result: Less cooling
Solution:
Low Ambient Controls / Head Pressure Controls
Standard refrigeration and A/C equipment are designed to operate above 60° ambient. Below that temperature none of the pressure-temperature relationships hold true and the system does not work correctly.
If the ambient air going through the condenser coils is too cold, the condensing temperature drops along with the heat pressure.
The metering device is designed to respond to a certain range of head pressures on the inlet of the device in order to ensure the proper pressure on its outlet.
Therefore, if the inlet pressure is too low, the pressure to the evaporator will also be low. A starved evaporator is the result, even if there is a high heat load on the evaporator.
The solution is to add low ambient controls to the condenser.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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22. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Head pressure control
Three common methods:
Fan cycling
Dampers
Flooding
Cycling the condenser fan:
When head pressure falls, the fan shuts off
When head pressure rises, fan starts
There are three types of head pressure control.
Cycling the condenser fan off and on to keep head pressure up.
Backing up refrigerant into the condenser (flooding).
Installing dampers on the condenser to block air flow.
Fan cycling is turning the condenser fan off if the head pressure falls below a certain minimum pressure. Usually, that minimum pressure is equal to the head pressure a 60° ambient
With the fan off there is no air flow through the condenser. Without air flow the heat is not released from the condensing gas and the head pressure starts to rise.
When the pressure reaches a predetermined higher pressure, the fan starts. The low ambient air being pulled through the condenser will lower the head pressure again. The fan continues to run until the head pressure control stops it.
The advantages of a fan cycle control are ease of installation and relatively low cost.
The main disadvantage is the wide swings of head pressure (usually 50 psig) cause changes in the pressure on the inlet of the metering device. These pressure fluctuations can cause erratic evaporator feeding by the metering device.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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23. Refrigeration Condenser Using Fan Cycle Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Refrigeration Condenser Using Fan Cycle Control
9/16/2018
R22 REMOTE CONDENSING UNIT - AMBIENT 78°
60o
220#
168#
Install Fan Control
DIFF.
HIGH EVENT
SWITCH LOW EVENT
IS HIGH EVENT
MINUS DIFF
500
400
300
200
100 50 25
150
Pressure falls
Compressor
C.C. HEATER
Fan cuts off
Rewire
If the air entering the condenser (ambient) is too cool then the pressures drop so much that the metering device cannot control the flow of refrigerant.
Most systems start having metering problems when the ambient goes below 60º.
At 60º an R22 refrigeration system would have a condensing temperature of 90º (60+30). The head pressure would be about 168#.
In the above example we will show how to keep the average minimum pressure above 60º by cycling the fan motor on the condenser.
To do this we have the fan cut off when the head pressure drops too low, and come back on when the head pressure builds back up.
For instance, when the system in the above example drops to 168# (60° ambient) the fan shuts off. The head pressure starts to rise and we could cut the fans on when it gets above 185# (equal to 66 ° ambient), but that would cause the fans to short-cycle on and off too rapidly.
So, we have the fan stay off until the pressure builds up to about 220#. We call this the control’s “cut-in” pressure. When the control contacts close, or “cut-in”, the fan starts. The pressures fall until the control opens (“cut-out”), stopping the fan at 168#. Then the cycle starts all over.
Fan cycle controls are easy to install. Just find a way to access the high pressure side of the system and redirect the wires going to the fan to break one power leg through the fan control.
CONDENSER
RECEIVER
60º Amb.+ 30º TD = 90º (168#)
78º Amb.+ 30º TD = 108º (220#)
Minimum Ambient = 60o
Ambient = 78o
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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24. Setting a Fan Cycle Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Setting a Fan Cycle Control
A fan cycle is a “reverse acting” HP control
When head pressure rises, the contacts close
“Rule of Thumb” settings for control:
Cut-out at 90° condensing
Cut-in at 110° condensing
For the following slide -
Cut-out is about 170 psig (R22)
Cut-in is about 225 psig
Differential is 55 psig
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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25. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Fan Cycle Control
9/16/2018
DIFF.
HIGH EVENT
SWITCH LOW EVENT
IS HIGH EVENT
MINUS DIFF
500
400
300
200
100 50 25
150
R22 System
“High Event” (Cut-in) = 225#
“Low Event” (Cut-out) = 170#
“Differential” (Difference) = 55#
SWITCH LOW EVENT
IS HIGH EVENT
MINUS DIFF
The rule of thumb is cut-out at 90° condensing and cut-in at 110° condensing.
Following is some of the logic to this rule. This is for a standard condenser with a 30 ° TD. If you are not sure of the correct setting, consult the manufacturer.
Above is a fan cycle control. The control will cycle the condenser fan off and on to maintain a minimum condensing temperature of 90º (60° ambient + 30° split). The head pressure of a R22 system at 90° condensing is about 170 psig. Therefore, we want the fan to shut off when the head pressure drops to 170#
Looking at the control above, the switch action is described on the control as “SWITCH LOW EVENT IS HIGH EVENT MINUS DIFFERENTIAL”.
What they are saying is the higher pressures on the right is the cut-in (high event).The lower numbers on the left are the difference, the amount the pressure will fall, before reaching the “low event” when the switch contacts open shutting off the condenser fan.
The condensing temperature we want the condenser fan to start is 110° (80° ambient + 30 °). The pressure of R22 at 110° condensing is 225#. This will be our controls cut-in or “high event”.
The differential will be about 55# for the fan to cut off at 170# (225-55).
The control settings will be cut-in at 225# with a 55# differential.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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26. Dampers for head pressure control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Dampers for head pressure control
Limits air flow through the condenser
Responds to:
Head pressure or
Ambient air temperature
Dampers control the head pressure by limiting the air flow through the condenser. Usually the dampers are located on the inlet air side of the condenser.
A motor control drives a rod that closes the dampers to maintain a minimum head pressure. The dampers have several positions, so they can maintain a relatively constant head pressure.
Dampers are especially useful when the condenser is subject to prevailing winds that would overcool the condenser, even if the fans are cycled off.
Dampers are fairly expensive and require occasional maintenance to lubricate the dampers and to make sure they are operating properly.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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27. Remote Commercial Condenser
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Separate System Circuits
Remote Commercial Condenser
Courtesy of Russell Coil Co.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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28. Condenser with Shutters
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Condenser with Shutters
9/16/2018
325#
125º cond.
R404A
This slides shows that during normal ambient conditions the dampers are full open.
Shutters full open
AMBIENT AIR (95º)
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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29. Condenser with Shutters 2
Ambient Temperature Drops
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
80º cond.
90º cond.
175#
205#
325#
125º cond.
R404A
Condenser with Shutters 2
Linkage and Shutter Blades move together
As ambient falls the dampers shut down to cut off some air flow.
This allows the condensing pressures to rise to the minimum head pressure the control is set for.
Airflow reduction raises head pressure
AMBIENT AIR (50º)
AMBIENT AIR (95º)
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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30. Condenser with Shutters 3
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Ambient Drops Further
9/16/2018
30º cond.
90º cond.
80º cond.
90º cond.
175#
205#
70#
205#
325#
125º cond.
R404A
Condenser with Shutters 3
As ambient drops to the lowest expected temperatures, the dampers may need to shut completely to bring the head up to the minimum setting.
Most units use a combination of fan cycle controls and dampers when used in areas where winter ambients are usually below freezing.
Airflow Fully Restricted Head Pressure Rises
AMBIENT AIR (0º)
AMBIENT AIR (50º)
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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31. Condenser Flooding “Head Pressure Regulator”
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Condenser Flooding “Head Pressure Regulator”
Backs up refrigerant into the condenser
Acts like an overcharge of refrigerant
Raises head pressure
Following is a sample of its operation
(See section on Valves for a more complete explanation)
Condenser flooding restricts the liquid from leaving a condenser and backs up or “floods” the condenser with liquid refrigerant. Before the hot discharge vapor from the compressor can condense into a liquid it must have space to “de-superheat” to the condensing temperature. By taking up the vapor space with liquid refrigerant the condensers “effective surface” has been reduced. This acts like an overcharge of refrigerant and maintains the designed head pressure.
Condenser flooding is one of the most effective means of maintaining a steady head pressure in cold weather. It is also the preferred method on equipment installed in the colder climates that have ambient temperatures dropping below +20°F.
One drawback is that this system usually requires an oversized receiver and more refrigerant. However, the larger amount of refrigerant backed up in the condenser increases subcooling which adds to the overall efficiency of the system.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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32. System with Head Pressure Regulator
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
System with Head Pressure Regulator
9/16/2018
Compressor
C.C. HEATER
Ambient ABOVE 60o
Normal Head Pressure
CONDENSER
RECEIVER
HPR open,
normal flow to receiver
This is a view of the entire system when the ambient is above 70º
Under these conditions the HPR valve is about as useful as an elbow in the liquid line from the condenser outlet to the receiver.
Ambient 80o
EVAPORATOR COIL
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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33. System with Head Pressure Regulator
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
System with Head Pressure Regulator
9/16/2018
Compressor
C.C. HEATER
Ambient BELOW HPR Setting
Cold ambient, cool liquid, low pressures
Head pressure increases
HPR slows liquid flow,
backing up refrigerant
CONDENSER
HPR bypasses discharge vapor
RECEIVER
Increases liquid temperature
As ambient temperatures fall, so does the temperature and pressure of the refrigerant in the condenser.
The HPR valve starts backing up the refrigerant into the condenser. This is like putting a cover over the condenser.
The head pressures rise to the setting of the HPR valve. Then the valve allows some hot gas to bypass straight into the liquid line to the receiver. At the same time some liquid from the condenser is allowed to pass and the mixture goes to the receiver.
Note, the reason for an HPR keep the pressures and temperatures up in the receiver so the TEV with have liquid at a proper temperature and pressure to function correctly.
Ambient 50o
EVAPORATOR COIL
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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34. Oil Pressure Safety Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Oil Pressure Safety Control
Protects compressor from lack of lubrication
Operates on pressure differential:
Oil pump discharge pressure
Minus suction pressure (pump inlet)
Net Oil Pressure must be above 10 psig
The oil pressure safety control, or “oil failure” control stops the compressor when there is not enough oil pressure to properly lubricate the compressor.
The control has two diaphragms. One to measure the suction pressure in the crankcase, the other to measure the pump outlet pressure.
Since the oil pump inlet is in the compressor crankcase it already has a pressure equal to whatever the suction pressure happens to be at the time it is checked. The oil pump simply increases that pressure.
Because the pump discharge pressure rises and falls with the suction pressure the control needs to subtract the suction pressure from the pump pressure. The result is called the net oil pressure.
Most manufacturers recommend about 30# net oil pressure for proper lubrication. However, during compressor start up that net oil pressure may drop momentarily without causing problems.
If the control stopped the compressor every time the net oil pressure dropped on start up there would be many nuisance trips.
Therefore, the control will allow the oil pressure to drop to about 10# before it takes any preventive action. At 9# the contacts close, energizing an electronic or heater circuit to allow an additional 90 to 120 seconds for the system to self- correct before it opens the circuit to the compressor. Once the circuit is opened it must be manually reset.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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35. Ranco Oil Safety Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Ranco Oil Safety Control
9/16/2018
To crankcase A 1
120 2
240 L M
To oil pump
Wiring diagram
Courtesy of Ranco Controls
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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36. Copeland’s Solid-state oil pressure control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Copeland’s Solid-state oil pressure control
9/16/2018
Pressure transducer
Same terminal markings
Copeland’s Solid-state oil pressure control
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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37. Oil Pressure Control Sequence
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Oil Pressure Control Sequence
Net Oil Pressure drops below 10 psig:
Contacts close to start timer
If pressure is low for 120 seconds it trips reset
Alarm contacts close
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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38. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Oil Safety Control L1 L2 L3
Timing
Circuit A L 2 M
SENTRONIC 
120v
240v CC CC CC
Timing
Circuit
Oil failure!
“Times Out”
Contacts open
Compressor off
This slide starts out with a pictorial electrical diagram of a three phase motor and contactor. The circuit for the contactor coil starts out at L1 (red), through the two operating controls (high pressure and low pressure), and to one side of the coil. The other side comes from L3 (black). When it reaches the coil (CC) it closes the three contacts (CC) and allows power to flow to the motor.
If the motor is on a large compressor it will need an oil safety control as one more operating control. The control is also placed in series with the contactor coil. Unlike the other controls, the oil safety needs another power wire (blue) to energize the timer when required.
This second wire is from the “load” side of the contactor so that it will only be energized if the contacts are closed and the compressor is running.
After about 120 seconds the control is “timed out”. This opens the switch between L and M, de-energizing the contactor coil and shutting down the compressor. At the same time a switch between L and A is closed. If so equipped an alarm light or bell will come on to tell the customer that the compressor has been shut off by the oil safety control. 2
Alarm contacts close 1 3
Operating Controls CC CC A
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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39. “Nuisance” Trips on Oil Safety Control
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
“Nuisance” Trips on Oil Safety Control
“Brown out”, low voltage to compressor:
Compressor goes off on internal overload
But control still has voltage
The control trips because of no oil pressure
Solution: Use a current sensing relay.
If the compressor is not drawing current it shuts off voltage to the control
Now the control only trips due to oil failure,
not low voltage problems
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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40. Current Sensing Relay One compressor wire through here
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Current Sensing Relay
9/16/2018
One compressor wire through here
Wires to oil control
Compressor current closes relay contacts
Prevents “nuisance” trips of oil control
if compressor is off on internal overload
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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41. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Defrost Clocks
2 types for Commercial Refrigeration:
Medium Temperature Refrigerators
Low Temperature Freezers
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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42. Refrigerator “planned” defrost
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Refrigerator “planned” defrost
9/16/2018
Need to plan for more “off-cycle” when:
Medium temperature box 34° to 36°,
Or heavy use, or high product load
Clock stops compressor:
Fans continue
1 - 2 hour off time
Melts all frost
Note: schedule when box is not in use such as middle of night
Sometimes the “off cycle” is not long enough to defrost the evaporator. This problem usually occurs when the box temperature is maintained between 34° and 36°. Or when the box receives very heavy usage from warm product or just excessive opening of the door.
We have to plan when, and how long, to shut off the compressor in order to clear the coils. For this reason, we call it a “planned” defrost and use a time clock to shut the compressor off long enough to accomplish the necessary defrost.
Usually the defrost is scheduled for a time when the box is not in use. For example, we may set the clock to go into defrost at 2:00 in the morning for 1 hour. This will give the coil enough time to melt the frost accumulated during the day. The product temperature may rise a few degrees, but not enough to cause food spoilage. When the defrost period is complete the compressor will quickly restore the product to its original temperature.
Note: below 34 ° box temperature, additional heat must be used to accomplish the defrost.
Example, meat cutters prefer meat at 28° because it is not frozen, but firm and easy to cut. Therefore, a meat box will have a medium temperature condensing unit, a medium temperature expansion valve, and a freezer coil with electric heaters to accomplish the defrost. Usually it only requires 2 short defrosts every 24 hours.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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43. “Planned” 115v Defrost Clock
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
2:00 AM
Trippers
4:00 AM
Dial
Rotation
Time of Day
This is a Paragon 4000 series clock that simply opens and closes a set of switches according to the setting of the “trippers”.
In this photo when the black tripper reaches 2:00 am a set of contacts will open and turn off the refrigeration. The silver tripper will closed the contacts and turn the refrigeration back on at 4:00 am.
(1) NC Switch
“Planned” 115v Defrost Clock L1 N
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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44. Commercial Refrigerator (35°)
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Commercial Refrigerator (35°)
“Planned” (Air) Defrost
Using a clock to schedule a long air defrost
35º
20º
Normal “off cycles” sometimes do not melt all the frost
Clock shuts off the compressor (usually at night)
Compressor off 1 or 2 hours
EVAPORATOR
Fans continue to run
20º
35º
Coil rises to 35° - 38°
All the frost melts
35º
30º
35º
20º
Space Temp. 35o
Coil clear, ready for next day
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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45. Low Temperature Evaporators (Freezers)
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Low Temperature Evaporators (Freezers)
Similar to other evaporators, except:
Defrost needs heat
Wider fin spacing
Low temperature evaporators are manufactured almost exactly like their medium temperature counterparts. However, they require some type of heat to melt the normal accumulation of frost. Also, because frost is expected when operating in air below freezing, the fin spacing must be wide enough to prevent frost bridging between fins for at least 4 to 6 hours of normal operation.
Air conditioning coils may have fin spacing of 15 fins per inch (fpi), while medium temperature units operate at 10 fpi. Freezer coils usually have a maximum of about 6 fpi.
Electric heaters are primarily used for defrost because the initial equipment cost is relatively low and can be used in all walk-in freezer installations.
Hot gas defrost is more expensive and requires extra piping and more exact piping procedures. Long piping runs may not allow this type of defrost to be used. However, under proper conditions, hot gas defrost is quicker and has lower operating costs.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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46. Frost Buildup on Refrigerators and Freezers
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Frost Buildup on Refrigerators and Freezers
9/16/2018
Frost is normal for refrigerators and freezers
On A/C coils the fin spacing is relatively close because there is a high volume of air blowing through an evaporator at a temperature above freezing.
On refrigerators and freezers the frost will build naturally on the tubes and fins because the coil temperature is below freezing.
Fin spacing on freezer coils is much wider than on refrigerator coils because there is a quicker frost build-up on the low temperature evaporators.
Freezers are sized to run almost continuously at their maximum design conditions. They stop only long enough to go through an electric or hot gas defrost.
Refrigerators:
light frost can “air defrost”
Fin spacing (fins per inch):
Freezers 4-8
Refrigerators 8-12
A/C 12-20
Freezers need heat
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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47. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Freezer Evaporator
This is an example of fin spacing.
This evaporator is about 7 fins per inch.
6 fins per inch
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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48. Defrosting Refrigerators and Freezers
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Defrosting Refrigerators and Freezers
Defrosting turns frost to water
During defrost the frost melts and is leaves the walk-in through the condensate drain line.
On freezers there is a fan delay to keep the fans from turning on until the coil temperature reaches about +25°. At this temperature any remaining droplets of water will refreeze and not be blown out into the walk-in when the fan starts.
Freezer fan delays prevent blowing water into box.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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49. Freezer Defrost Sequence
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Freezer Defrost Sequence
Initiated by time clock
Fans shut off, heaters turned on
Terminated by temperature or time
Heaters off, compressor on, fans delayed
Fans on (when coil drops to 25°)
Note:
Refer to “Electrical HVACR Controls” CD for wiring sequence.
The number of defrosts per day and the maximum length of defrost time depend on the conditions of operation and the location of the equipment. For instance, in the Washington, D.C. area the high heat and humidity during the summer requires 4 defrosts in a 24 hour period. Under normal design conditions a defrost will last for only about 15 minutes. However, the defrost clock has a “fail safe” that will allow defrost to occur for up to 45 minutes for those abnormal times when the box was loaded with more product or the door was open longer than usual.
In Phoenix, AZ the heat may be high, but the humidity is low. There is usually less coil icing in dry parts of the country where they may only use 2 defrosts a day.
The defrost is initiated, or started, according to the defrost clock setting. The fans stop and the electric heaters (or hot gas) starts warming the coil. When the coil reaches a temperature high enough to have melted all the frost, a temperature sensor called the defrost termination switch takes the coil out of defrost and returns it to refrigeration operation.
The fans stay off until the heat from defrost is removed from the coil and any droplets of water formed during defrost have now been refrozen. The fan delay switch restart the evaporator fans which run continuously until the next defrost.
Note, the defrost operation is also important for proper oil return. During the freeze cycle the cold oil tends to become trapped in the evaporator. The heat from defrost warms it sufficiently to return it to the compressor on start up.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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50. Picture of Coil defrost heaters
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Electric Defrost Heaters
Picture of Coil defrost heaters
Heater Safety
DTFD
(defrost termination / fan delay)
The end of this freezer evaporator shows:
The defrost heaters.
Terminal board for defrost wiring connections.
The wires from the time clock are attached at this location
The combination defrost termination – fan delay 3-wire control.
This stops defrosts and switches the system back into cooling, also, it delays the fan from starting until the coil is about 25°
A heater safety.
The larger 2-wire control opens the circuit to the heaters if the temperature is too high. It is a backup to the defrost termination.
Wiring Terminal Board
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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51. Freezer Defrost clock (front & rear)
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
Fail Safe Setting
9/16/2018
Defrost Solenoid
TIME
Defrost Clock Motor
Defrost Pins
Slide
This is a front and rear view of the popular Paragon defrost clock used on many walk-in freezers.
On the rear view on the right, note the slide that switches the contacts from defrost to freeze.
Also, note the defrost termination solenoid in the upper right hand corner.
Contacts
Freezer Defrost clock (front & rear)
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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52. Defrost Using Internal Heat (Hot Gas Defrost)
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Defrost Using Internal Heat (Hot Gas Defrost)
Uses hot gas from compressor discharge,
Enters inlet of the evaporator
Defrosts from “inside out”
The internal heat method of defrost normally uses the hot gas from the compressor. This hot gas can be introduced into the evaporator from the compressor discharge line to the inlet of the evaporator and allowed to flow until the evaporator is defrosted.
The defrost cycle is usually started by the timer (time initiated) and can be stopped by either time or according to the temperature of the evaporator (time or temperature terminated).
When the defrost is terminated the refrigerating cycle is re-started.
The following example demonstrates how hot gas defrost is accomplished.
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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53. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
Hot Gas Defrost
Hot Gas Solenoid Valve
CPR
Valve
Opens
Compressor
Condenser
Frost melts
Frost buildup
This slide shows how the hot gas valve opens and sends discharge vapor from the condenser toward the evaporator.
The vapor enters the distributor downstream of the expansion valve.
The hot gas warms the evaporator melting any frost build up on it.
Evaporator
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
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54. © 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
R3 Controls, Valves, Accessories & Heat Pumps - Subject 1 Controls v1.1
9/16/2018
End of
Controls
© 2004 Refrigeration Training Services - R3 Subject 1 Controls v1.2
© 2004 Refrigeration Training Services
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