E3 HVACR Controls and Devices

E3 HVACR Controls and Devices
#2 Relays, Refrigeration Controls, and Timers

Understanding Relay Terminology
The following slides illustrate: Contacts Poles Throws Switching © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Contacts Contacts opening a circuit Contacts closing a circuit
Contacts closing this circuit Contacts closed Contacts opening this circuit Contacts closing this circuit © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Poles The number of sets of contacts that can be switched at one time.
© 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Switch Poles Single pole (SP) Double pole (DP) Three pole (3P) 1 1 2 1

Throw The number of positions the contacts move to complete a circuit.

Throw Single Throw (ST) Single Throw (ST) Double Throw (DT) Throw
1 2nd Throw © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Normal Positions Normally Open (NO) Normally Closed (NC)

Relay Arrangements Name the contact arrangements on the following drawings. The number of poles The number of throws Which contacts are normally open (NO) Which contacts are normally closed (NC) © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Name The Switching Arrangements
Poles Throws Positions Single Pole SP Double Pole DP Three Pole 3P SPST (NO) ? Single Throw ST Double Throw DT SPST (NC) ? Normally Open NO Normally Closed NC (NC) ? ? SPDT ? (NO) © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Double Break Contacts The following slides have double contact arrangements that make and break at the same time © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Double Break Contacts Single Pole
SPST SPDT © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Double Break Contacts Double Pole
DPST DPDT © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Switching Relays Following is a common fan relay
It has both normally open and normally closed contacts It also uses a double pole, double throw (DPDT) switching arrangement © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

General Purpose Relay Relay Switch Contacts Relay Coil Drawing of a
White-Rodgers relay © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Relay Terminals Relay coil terminals Top View
Normally CLOSED contacts: Normally OPEN contacts: 2 1 1 3 4 6 1 3 2 5 1 to 2 1 to 3 4 to 5 4 6 4 5 4 to 6 Relay coil terminals Drawing of a White-Rodgers relay © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Relay Cut-away View Coil Energized pulls plunger down 3 2 1
Drawing of a White-Rodgers relay © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Relay Cut-away View 1-2 opens Coil 1-3 closes Energized pulls plunger
down Drawing of a White-Rodgers relay © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Commercial Refrigeration Controls
Pump-down solenoid valves Defrost Clocks Defrost controls Low & high pressure controls Oil safety controls Crankcase heaters and controllers © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Solenoid Valve Operation
Magnetic coil energized, lifts plunger Fluid lifts seat, flows through valve Magnetic coil de-energized, plunger falls Fluid pressure on seat helps close valve © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Magnetic coil energized
Solenoid Valve Magnetic coil energized Plunger pulled up Power off Plunger drops Fluid flows Plunger Fluid stops Seat © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Commercial Refrigeration Defrost
Medium temperature refrigerators use the thermostat “off-cycle” to melt frost accumulation Sometimes a time clock is needed to extend the length of the “off-cycle”. Following is a common wiring arrangement for a walk-in refrigerator © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Walk-in Refrigerator with Pump-down Solenoid Refrigerating Cycle
Off-Cycle Defrost Thermostat Satisfied TS L 120V Solenoid Opens N Solenoid Closes JUNCTION BOX This is the basic wiring of a walk-in refrigerator that uses a thermostat and pump-down solenoid. When the thermostat is satisfied it breaks the circuit to the solenoid coil, closing the solenoid and stopping the flow of liquid to the expansion valve. The compressor runs until the suction pressure drops to the cut-out setting on the low pressure control. The fans are wired to run continuously so the air in the box continues to circulate after the compressor is off. Since the box is above freezing it will defrost the evaporator coil. A solenoid should be used whenever you have a remote condensing unit for at least 2 reasons. First, when the solenoid closes it will pump all the refrigerant out of the low side of the system and store it in the receiver before the compressor shuts down. This prevents refrigerant migration and flooded starts. Second, the compressor has an easier time starting from an unloaded condition. EVAPORATOR COIL © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Common Time Clock Used for cycling outdoor lights, heaters, etc.
Clock in the example has one set of normally closed (NC) contacts It is cycling a refrigeration compressor for an extended off-cycle © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

115 Volt Time Clock Trippers “OFF” @ 2:00 AM Dial Rotation
4:00 AM Time of Day 115 Volt Time Clock (1) NC Switch 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. L1 N Load © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Time Clock in Refrigeration
“Planned” off-cycle defrost This gives the evaporator extra time to air defrost The clock shuts off the compressor while the evaporator fans continue to run © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Defrost Clock on a Walk-in Refrigerator Refrigerating Cycle
“Planned” off-cycle defrost Contacts open DEFROST CLOCK TIMER MOTOR TIMER MOTOR Circuit opens Compressor off for 1-2 hours 2 1 N Change wiring Change wiring Evaporator will air defrost TS L 120v Solenoid Closes N A “planned” defrost is required when someone is running a walk-in cooler too cold (34°-36°), or keeping the doors open too much, or putting hot product in the box. Any of these will cause the system to run too long without it’s standard “off-cycle” defrost from the thermostat. The long run time will cause the evaporator to accumulate frost, which must be eliminated at least once a day. The “B” or blue wire is the Common wire. The contacts on the 1-2 switch are not controlling anything in this example. They just happen to be there on the Paragon clock that uses a 230 volt circuit. If it were a 115 volt fan a Paragon clock could be used. The “A” or red wire is broken through the 3-4 contacts which control one side of the pump-down solenoid valve. Note, the fans must continue to run while the compressor is off so that the above-freezing air in the cooler will defrost the evaporator. The most popular defrost time for these units is about 2:00 AM for one or two hours. That is usually enough time to get rid of the frost buildup during the day and it is done while there is nobody around to open the doors which could cause over-heating of the box. JUNCTION BOX EVAPORATOR COIL © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Low Temperature Evaporator Design
Heaters A freezer requires some heat to help defrost the evaporator Defrost termination and fan delay Controls are needed to return system to freeze Heater Safety Prevents overheating of freezer A clock is needed to control defrost and freeze cycles Low-temperature evaporators all operate below freezing and must have planned defrost. Because the air inside the refrigerated box is well below freezing, heat must be added to the evaporator for defrost. This defrost is normally accomplished with external heat or internal heat. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Electric Defrost Heaters
Heater Safety DTFD (defrost termination / fan delay) Electric Defrost Heaters 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 © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Defrost Clock (Back and Front)
SOLENOID SLIDE CONTACTS © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Defrost Settings and Wire Terminals
The following clock is scheduled for 4 defrosts in 24 hours The “failsafe” setting is a backup to the defrost termination switch If the defrost lasts too long (about 45 minutes on the sample clock) the failsafe will put the system back into freeze © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

X 4 3 1 2 N Time Clock Paragon 8145-20 TIME FAIL SAFE TIME FAIL SAFE
6 7 8 9 10 11 12 1 2 3 4 5 50 40 60 30 20 10 2 70 80 90 100 110 FAIL SAFE TIME FAIL SAFE SET POINT DEFROST TRIPPERS CLOCK TIME FREEZE X 4 3 DEFROST DEF. TERM. 1 2 N COMMON POWER © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

X 4 3 1 2 N Time now set for 6 pm Set Time Time Clock TIME 6 7 8 9 10
11 12 1 2 3 4 5 50 40 60 30 20 10 2 70 80 90 100 110 Time now set for 6 pm Set Time X 4 3 The internal mechanism includes an electric clock that continually turns the dial on the front of the clock. As the trippers line up with the “time” pointer the system is forced into a defrost. Setting the proper time of day, or manually turning the system into a defrost is accomplished by turning the center of the dial in the counter clockwise direction. Note, when this slide is printed out, the time pointer is actually indicating a little after 1:00 PM. In the “slide show” the dial will rotate until it lines up with the pointer at 6:00 PM. Then the text, “Time now set for 6 pm”, will appear. 1 2 N © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Defrost Clock and Wiring
The following is a pictorial diagram of the clock, the evaporator, and the controls. The color coded wiring as illustrated is typical of most walk-in freezers The sample system is in the freeze cycle External heat type of defrost is usually accomplished by using factory-installed electric heaters embedded in the fins of the evaporator. The external heat method is usually not as efficient as the internal heat method. However, it is the only practical method when the condensing unit is far from the evaporator. If we tried to use hot gas defrost the long piping run would cool the hot gas, possibly condensing it to a liquid. This would result in longer defrost times and possible compressor damage due to floodback. Yes, even with a suction line accumulator, there is a chance of floodback to a compressor if we send too much liquid back through the suction line. The following is a description of the basic series of events during a the electric external heat type of defrost: Both the compressor and the evaporator fan stop when the timer initiates defrost. The electric defrost heaters and pan heaters are energized. The time clock will switch back into the freeze cycle when the defrost termination control senses the coil has warmed sufficiently to melt all the frost. If there is a problem with the defrost termination switch a timed fail-safe switch will switch the clock back into freeze. The compressor will start The evaporator fan will not come on (delayed) until the evaporator temperature has dropped to below freezing. This prevents droplets of water and heat from the heaters from being blown out into the box. Refer to the following example of the defrost cycle for a more complete description. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Wiring Diagram for W/I Freezer with Electric Defrost & Remote C.U.
DEFROST SOLENOID CLOCK MOTOR 3 DEFROST HEATERS SLIDE ↔ EVAP FAN 4 DEFROST TERMINATION FAN DELAY 3 4 X X Brn R N N Blk Operation of a freezer using the Paragon Model defrost clock. Freezing Mode: Contacts #2 and #4 close, sending power to #4 on the evaporator. This energizes the red wire to the freezer thermostat, to the evaporator fan, and to the drain line heater. Note: N (blue) is used as the common wire. Defrost Mode: Defrost is time-initiated by the defrost clock. Following is the sequence of operation: The contacts open between #2 and #4, shutting off the t-stat, fan, and the drain heater. The contacts close between #1 to #3, sending power to #3 on the evaporator, energizing the defrost heater. When #3 on the clock was energized it also sent power to one side of the defrost termination solenoid behind the front panel of the clock, next to the clock motor. When the heaters warm the evaporator up to about 55° the contacts close between R and B (brown) on the DTFD (defrost termination/fan delay) control. This allows the common to go through X to the other side of the defrost solenoid. When energized the defrost solenoid coil pulls in a lever which mechanically changes the switch positions. Contacts #1 to #3 now open, shutting off power to the defrost heater. Contacts #2 to #4 are now closed returning it to the freezing mode (see above). Note #1 The evaporator fan stays off after defrost because the DTFD contacts are open between R and Black. They will close when the evaporator cools down to 25°. By delaying the fan until any droplets of water are refrozen to the evaporator, we prevent the warm defrost air from blowing water into the freezer. One indication of a bad fan delay would be icicles on the ceiling and ice on the fan blades. Note #2 The defrost clock is continually running in both freezing and defrost. If the DTFD does not bring the system out of defrost, there is a backup, or “Fail Safe”, setting on the inner-dial of the clock face. Normal defrost only takes about 20 minutes, but may be longer when there is more ice formation than normal. If, for any reason, the defrost continues to the setting on the fail safe (usually 45 minutes) it will put it back in the freeze mode. Note #3 the defrost solenoid is only energized for a second, time enough for the mechanical lever to pull up changing the contacts from the defrost mode to the freeze mode. 1 2 SOLENOID VALVE THERMOSTAT LINE VOLTAGE TO CLOCK DRAIN LINE HEATER © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Defrost clock and Heaters
Defrost is “time initiated” The clock movement pushes the slide bar on the rear of the clock. The slide changes the switch contact positions from freeze to defrost External heat type of defrost is usually accomplished by using factory-installed electric heaters embedded in the fins of the evaporator. The external heat method is usually not as efficient as the internal heat method. However, it is the only practical method when the condensing unit is far from the evaporator. If we tried to use hot gas defrost the long piping run would cool the hot gas, possibly condensing it to a liquid. This would result in longer defrost times and possible compressor damage due to floodback. Yes, even with a suction line accumulator, there is a chance of floodback to a compressor if we send too much liquid back through the suction line. The following is a description of the basic series of events during a the electric external heat type of defrost: Both the compressor and the evaporator fan stop when the timer initiates defrost. The electric defrost heaters and pan heaters are energized. The time clock will switch back into the freeze cycle when the defrost termination control senses the coil has warmed sufficiently to melt all the frost. If there is a problem with the defrost termination switch a timed fail-safe switch will switch the clock back into freeze. The compressor will start The evaporator fan will not come on (delayed) until the evaporator temperature has dropped to below freezing. This prevents droplets of water and heat from the heaters from being blown out into the box. Refer to the following example of the defrost cycle for a more complete description. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Defrost Cycle and Termination
DEFROST SOLENOID Start Defrost Cycle CLOCK MOTOR End Defrost Cycle 3 4 EVAP FAN DEFROST TERMINATION FAN DELAY 3 4 X X Brn DEFROST HEATERS R 1-3 open 1-3 closed 2-4 open 2-4 closed N N Blk Defrost Mode: Defrost is time-initiated by the defrost clock. Following is the sequence of operation: The contacts open between #2 and #4, shutting off the t-stat, fan, and the drain heater. The contacts close between #1 to #3, sending power to #3 on the evaporator, energizing the defrost heater. When #3 on the clock was energized it also sent power to one side of the defrost termination solenoid behind the front panel of the clock, next to the clock motor. When the heaters warm the evaporator up to about 55° the contacts close between R and B (brown) on the DTFD (defrost termination/fan delay) control. This allows the common to go through X to the other side of the defrost solenoid. When energized the defrost solenoid coil pulls in a lever which mechanically changes the switch positions. Contacts #1 to #3 now open, shutting off power to the defrost heater. Contacts #2 to #4 are now closed returning it to the freezing mode (see above). Note #1 The defrost clock is continually running in both freezing and defrost. If the DTFD does not bring the system out of defrost, there is a backup, or “Fail Safe”, setting on the inner-dial of the clock face. Normal defrost only takes about 20 minutes, but may be longer when there is more ice formation than normal. If, for any reason, the defrost continues to the setting on the fail safe (usually 45 minutes) it will put it back in the freeze mode. Note #2 the defrost solenoid is only energized for a second, time enough for the mechanical lever to pull up changing the contacts from the defrost mode to the freeze mode. 1 2 THERMOSTAT SOLENOID VALVE LINE VOLTAGE TO CLOCK DRAIN LINE HEATER © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Switching from Defrost Back Into Freeze
When the defrost termination switch is warm enough (usually 55°), the clock’s defrost solenoid is energized The solenoid mechanically moves the slide, switching the contacts out of defrost and back into freeze The fan is delayed until the temperature of the evaporator is down to approximately 25° External heat type of defrost is usually accomplished by using factory-installed electric heaters embedded in the fins of the evaporator. The external heat method is usually not as efficient as the internal heat method. However, it is the only practical method when the condensing unit is far from the evaporator. If we tried to use hot gas defrost the long piping run would cool the hot gas, possibly condensing it to a liquid. This would result in longer defrost times and possible compressor damage due to floodback. Yes, even with a suction line accumulator, there is a chance of floodback to a compressor if we send too much liquid back through the suction line. The following is a description of the basic series of events during a the electric external heat type of defrost: Both the compressor and the evaporator fan stop when the timer initiates defrost. The electric defrost heaters and pan heaters are energized. The time clock will switch back into the freeze cycle when the defrost termination control senses the coil has warmed sufficiently to melt all the frost. If there is a problem with the defrost termination switch a timed fail-safe switch will switch the clock back into freeze. The compressor will start The evaporator fan will not come on (delayed) until the evaporator temperature has dropped to below freezing. This prevents droplets of water and heat from the heaters from being blown out into the box. Refer to the following example of the defrost cycle for a more complete description. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

3 4 3 4 X X N N 1 2 R Energized solenoid moves slide
Return to Freeze Cycle DEFROST SOLENOID Energized solenoid moves slide CLOCK MOTOR Evap Cools, Fan Starts 3 4 EVAP FAN DEFROST TERMINATION FAN DELAY 3 4 X X Brn DEFROST HEATERS R 1-3 open 1-3 closed 2-4 open 2-4 closed N N Blk 1 Operation of a freezer using the Paragon Model defrost clock. Freezing Mode: Contacts #2 and #4 close, sending power to #4 on the evaporator. This energizes the red wire to the freezer thermostat, to the evaporator fan, and to the drain line heater. Note: The evaporator fan stays off after defrost because the DTFD contacts are open between R and Black. They will close when the evaporator cools down to 25°. By delaying the fan until any droplets of water are refrozen to the evaporator, we prevent the warm defrost air from blowing water into the freezer. One indication of a bad fan delay would be icicles on the ceiling and ice on the fan blades. 2 THERMOSTAT SOLENOID VALVE LINE VOLTAGE TO CLOCK DRAIN LINE HEATER © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Pressure Switches Stop and Start current flow
Energize or de-energize refrigeration components Typical pressure switches: Low Pressure switch – Closes on rise High Pressure switch – 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. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Low Pressure Control Differential Cut-in

Low Pressure Control Cut-out Cut-in

Fan Cycling for Controlling Head Pressure
Use a “reverse acting” high pressure control Contacts close on pressure rise Fan cycling is the simplest means of head pressure control and is used extensively in areas where the normal lowest ambient temperatures are above +20° F. The control is a “reverse acting” high pressure control which “makes” (closes) its electrical contacts on a rise in pressure. The control stops the condenser fan when the head pressure is below a certain setting. This is known as the “cut-out”. It starts the fan when the head pressure has risen to the “cut-in” setting. This cycle continues as long as the ambient air is cool enough to drop the head pressure when the fan is started. If there is more than one fan, the other fan(s) may be cycled by a thermostat according to the ambient air temperature. The last fan to run is the one controlled by the pressure control. Even with the fans off the head pressure can drop if there are winds that blow through the condenser coils. We will deal with that situation in section Air Volume Control for Head Pressure. The next slide will show you how cycling the condenser fan will control the head pressure. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Controlling Head Pressure in Low Ambients with a Fan Cycle Control
BELOW 60o REMOTE CONDENSING UNIT - AMBIENT 78° 168# 220# 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 78º Amb.+ 30º TD = 108º (220#) 60º Amb.+ 30º TD = 90º (168#) Minimum Ambient = 60o Ambient = 78o © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Oil Pressure Safety Control
Protects compressor from lack of lubrication It is a pressure differential control: Measures suction pressure (pump inlet) Measures oil pump discharge pressure Net Oil Pressure must be above 10 psig If not, timer starts After 120 seconds the controls trips out 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. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Ranco Oil Safety Control
To crankcase 1 A 120 2 240 L M To oil pump Wiring diagram © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Oil Safety Wiring The following diagram opens as a typical 3Ø refrigeration unit Then an oils failure control is added The important points to notice are: A common wire is needed to operate the timer When oil pressure drops there is a 2 minute delay before the control contacts open These controls have terminals for a remote alarm to notify the owner of a problem 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. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Adding an Oil Safety Control
Compressor and Contactor L1 L2 L3 Common wire needed for timer 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 90 to 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. 1 2 3 Alarm contacts close Operating Controls CC Standard compressor operation A © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Crankcase Heaters There are several types of crankcase heaters
They are used to boil off any refrigerant in the oil during the off cycle 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. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Types of Crankcase Heaters
Semi-Hermetic Compressors Hermetic Compressors Internal & External Heaters Strap Type Heaters © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Wiring of Crankcase Heaters
Heaters should be energized only when the compressor is OFF There are at least 2 methods to do this Use an auxiliary switch on the contactor Wire leads across an open set of contacts © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Use an auxiliary switch on the contactor
Compressor ON Compressor OFF Contactor Open Contactor Closed L1 L2 Auxiliary contacts close Auxiliary contacts are open C R S This slide shows how an auxiliary switch on a contactor will be closed when the compressor is off. The heater will then be energized. When the compressor is running the switch is open and the heater is off. Heater turns ON Heater is OFF © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Wiring across the contactor
Compressor ON Compressor OFF L1 L2 0v 120v Contactor Open Contactor Closed No potential difference, 0 volts Electrical potential,120 volts C R S This slide shows how an auxiliary switch on a contactor will be closed when the compressor is off. The heater will then be energized. When the compressor is running the switch is open and the heater is off. Heater is OFF Heater turns ON © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Time Delays Solid-State timers: Delay on open, or on closing
Some have adjustable time period Wired in series with control © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Delay Timer Power to load. Circuit closes. C Add Timer
MINUTES 5 .03 LOAD INPUT VAC 3 1 CUT WIRE FOR VOLT 1.5 AMP MAX DELAY ON MAKE TIMER Power to load. Circuit closes. HPS CT C LPS TRANS Add Timer Temperature rises C 1 3 Timer 1 3 Timer Tstat Closes Timed Out © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Preventing Short Cycling
Anti-Short-Cycling Devices Commonly used in low voltage to prevent compressor short cycling Wired in parallel with control Usually fixed time off period of 5 to 7 minutes Troubleshooting these devices: If it’s not delaying, it’s bad. © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Anti-Short-Cycling Device
T-STAT 24 VAC SHORT CYCLE PROTECTOR 2 AMPS at 24VAC RESISTIVE 5 Min. DELAY -Y -C Y1- C1- TRANS Temperature rises Timer Y Y1 C C1 Timer Y Y1 C C1 Add Timer Tstat Closes C C Timed Out CT HPS LPS © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

Heat Pump Defrost Following is a basic defrost module for heat pumps

Solid-State Heat Pump Defrost Module
Control Power (24 Volts) Defrost Defrost Relay Coil (18v DC) Thermistors sense cold condenser, energize defrost relay Defrost warms condenser thermistors, de-energize defrost relay AC DR DR AC Coil Air T Thermistor in condenser coil T Thermistor in condenser airflow © 2005 Refrigeration Training Services - E3#2 Relays, Refrigeration Controls and Timers v1.0

END OF Relays, Refrigeration Controls and Timers

E3 HVACR Controls and Devices

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E3 HVACR Controls and Devices

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