E3 HVACR Controls and Devices #1 Thermostats and Heating controls

Line Voltage Thermostats Primarily used in refrigeration equipment Electro-mechanical type uses a sensing bulb and bellows to operate switching Electronic type uses a circuit board and thermistor Refrigeration tstats require adjustable cut-in cut-out differentials © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Line Voltage Electronic Tstat Circuit board Line Voltage Electronic Tstat Thermistor This tstat is sensing evaporator temperature: Cuts-out when the coil temperature drops to 25°. Cuts-in when the coil temperature rises to 37°. © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Line Voltage Refrigeration Tstat Cut-out Differential Cut-in Temperature Sensing Bulb Bellows Line Voltage Refrigeration Tstat © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Low Voltage Thermostats Safer than high voltage tstats (24 volts) Close temperature differential (usually 2°) Uses smaller wires (18 gauge) Requires a step-down transformer © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Step-down Transformer L1 T1 240 volt Primary Induced voltage 24v Secondary T2 L2 Ratio 10 : 1 Voltage 240 : 24 © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

High Voltage / Low Voltage Circuits Low voltage controls can control high voltage loads © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Low voltage & High voltage Circuits COMP C C CFM A 240 volt motor is controlled by a 24 volt thermostat. IFM IFR C CR HPS LPS CIT 240v The schematic diagram is built step-by-step. Each line, switch, and load is brought in by mouse clicks. Although the instructor has to click many times, it gives complete control over pointing out what is happening as each action is initiated. At the end, students are often amazed by how easy it is to understand a complex diagram when it is built in stages. TRANS 24v G On IFR Check out fan circuit Auto Turn Fan “ON” R Y CR CT © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Low Voltage Thermostat Following is a standard Honeywell diagram The standard low voltage color code is: Red for power to the thermostat White for heat Yellow for cool Green for fan © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Honeywell Q539A Subbase B O W Y G R B O W Y G R COOL OFF HEAT ON FAN AUTO B O W Y G R 70 80 60 50 OFF POSITION B O W Y G R Red is always energized Color coded wires to tstat Fan Relay Gas Valve Compressor Contactor POWER TO THERMOSTAT POWER COMMON TRANSFORMER Adapted from a diagram by Honeywell Controls © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Thermostat Switching The front portion of a thermostat contains the temperature sensors The subbase contains the switches and circuits to direct the power where it is needed © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Switch to Cool B G Y R W OFF POSITION FAN AUTO COOL POSITION CALL FOR COOLING AUTOMATICALLY STARTS FAN POWER TO 'G' B G Y R POWER TO 'Y' THERMOSTAT CALLS FOR COOL W Fan Relay Fan Relay Gas Valve Compressor Contactor Compressor Contactor POWER TO THERMOSTAT POWER COMMON TRANSFORMER Adapted from a diagram by Honeywell Controls © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Thermostat and Subbase The next slide shows how the Thermostat and the Subbase are electrically connected. © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Combination Diagram T87F Tstat (top) Q539A Subbase (bottom) R1 R1 Temp. Rises TEMPERATURE RISES R1 R1 T87F Tstat (top) Fixed cool anticipator Adjustable heat anticipator COOLING ANTICIPATOR HEATS UP W1 W1 Y1 Y1 FAN COOL POSITION HEAT OFF COOL AUTO ON W Y Y G G R R Q539A Subbase (bottom) Gas Valve Compressor Compressor Fan Relay Fan Relay POWER TO THERMOSTAT Adapted from a diagram by Honeywell Controls © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Anticipators Human comfort requires a 2° temperature differential The tstat must “anticipate” the room temperature Heating and cooling anticipators are needed to maintain a close differential The following slide shows what would happen if the tstat did not have a heat anticipator during a heating cycle © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

T-Stat Operation Without a Heat Anticipator Tstat cycles on Room begins to warm Residual furnace heat overheats the room 72 73 74 75 76 77 78 79 80 Tstat cycles off (OVERSHOOT) Room Temperature Comfort Zone 2 Diff. 4 Diff. (LAG) Room temperature falls while furnace heats up Time © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

With Heating Anticipator When the heating thermostat cycles on the heat anticipator starts to warm The anticipator’s heat “fools” the thermostat into shutting off a little sooner The room temperature stays within a 2° swing © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

T-Stat Operation With a Heat Anticipator 80 Tstat Cycles on 79 Residual heat warms room to 76° Room Warms 78 Tstat cycles off 77 Room Temperature 76 Comfort Zone 2 Diff. 75 74 73 Heat anticipator warms thermostat Because tstat “thinks” it is 77 72 Time Room temperature falls while furnace heats up © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Basic Gas Heating Controls Three types of controls: Fan controls Safety controls Ignition controls A fan control delays the blower until the heat exchanger is warm Note: It also delays blower shut down after burners have cycled off © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Heating Mode – Auto Fan Comp 5 - Fan motor starts on low speed 1 2 3 4 5 6 7 9 8 10 C C CFM IFR High 5 - Fan motor starts on low speed Low IFM 4 - Furnace heat rises, fan switch closes FS TRANS G On IFR 3 - Gas valve opens (3,4) Auto Cool Y CR 2 - Room temperature falls (1) R Off CT 1 - Switch t-stat to heat W GV LS Heat HT © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Furnace OVERHEATS Comp L1 L2 Comp 1 2 3 4 5 6 7 9 8 10 C C CFM IFR High 3 –Blower runs until heat exchanger has cooled down Low IFM FS TRANS G On IFR (3,4) Auto Cool Y CR 2 – Gas valve shuts off (1) R Off CT 1 – Limit switch opens W GV GV LS Heat HT © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Gas Furnace Direct Ignition There are more components in a direct ignition system than on the old standing pilot furnaces The next slide will introduce those components as well as the high voltage connections of the system © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Gas Direct Ignition Controls L1 (HOT) High Voltage Adapted from a diagram by Honeywell Controls THERMOSTAT COMBUSTION AIR BLOWER MOTOR R G HIGH LIMIT SWITCH Y W DUAL GAS VALVE BLOWER RELAY Combustion Air FAN CENTER VALVE VALVE (GND) 24V TH-W 24V-GND GND (BURNER) VENT DAMPER PLUG L2 HSI L1 MV R C Transformer AIR PROVING SWITCH HOT SURFACE IGNITER- SENSOR Y G W FAN RELAY Relay coil Burner Ground FAN LIMIT HOT SURFACE IGNITION CONTROL Lo C Hi FAN MOTOR © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Although complex, the low voltage wiring is logical Direct Ignition Although complex, the low voltage wiring is logical On a call for heat the following sequence occurs: The combustion blower starts The air proving switch closes sending low voltage to the control module The igniter and gas valve are energized © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Gas Direct Ignition Controls L1 (HOT) High Voltage Adapted from a diagram by Honeywell Controls THERMOSTAT Tstat calls for Heat COMBUSTION AIR BLOWER MOTOR ON R R G HIGH LIMIT SWITCH Y W W DUAL GAS VALVE Gas valve energized BLOWER RELAY Combustion Air FAN CENTER Igniter Energized MV MV VALVE VALVE (GND) 24V TH-W 24V-GND GND (BURNER) VENT DAMPER PLUG L2 HSI L1 R R C C Low Voltage AIR PROVING SWITCH Y G W Air Switch Proven HOT SURFACE IGNITER- SENSOR W FAN RELAY Relay coil Burner Ground FAN SWITCH Fan switch closes HOT SURFACE IGNITION CONTROL Lo Lo Burners warm heat exchanger C C Hi FAN MOTOR © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Electric Heating Controls Electric resistance heaters are used for: Supplemental heaters in heat pumps Duct heaters Sequencers Provide a time delay for each heater Prevents high initial current draw © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Schematic of Electric Heaters with Sequencers 1st Heater is ON M2 M1 IFR NO High IFM IFM Blower Starts FAN SWITCH Switch to HEAT Low NC Energize Sequencer #1 TRANS Seq #1 also closes A1-A2 LS SEQ #2 Auto On G IFR SEQ #3 A1 A2 A1 A2 SEQ #1 Y CR SEQ #2 R CT W Heat-Cool Switch FAN SWITCH SEQ #1 HT © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Schematic of Electric Heaters with Sequencers 3rd Heater is ON M2 M1 SEQ #2 M2 M1 2nd Heater is ON SEQ #1 M2 M1 IFR NO High The heat is on and the blower is running until the thermostat is satisfied. IFM IFM FAN SWITCH Low NC TRANS LS SEQUENCER #3 SEQ #2 Auto On G IFR SEQ #3 A1 A2 A1 A2 SEQ #1 Y CR SEQ #2 R CT SEQUENCER #2 W Heat-Cool Switch FAN SWITCH SEQ #1 HT © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Thermostat (T/S) Troubleshooting Chart Adapted from Honeywell, Inc T/S jumpered; system won’t start. T/S jumpered; system works Room temp. overshoots T/S setting; too cold Reach setting; too warm Room temp. doesn’t System cycles too often System doesn’t cycle often enough PROBLEMS: Room temp swings excessively. SOLUTIONS: T/S not at fault; check elsewhere T/S wiring hole not plugged; drafts T/S not exposed to circulating air T/S not mounted level (mercury switch types) T/S not properly calibrated T/S exposed to sun, source of heat T/S contacts dirty T/S set point too high T/S set point too low T/S damaged T/S located too near cold air register Break in T/S circuit Heat/Cool Anticipator; System size © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

Thermostat (T/S) Troubleshooting Chart (No animation) Adapted from Honeywell, Inc T/S jumpered; system won’t start. T/S jumpered; system works Room temp. overshoots T/S setting; too cold Reach setting; too warm Room temp. doesn’t System cycles too often System doesn’t cycle often enough PROBLEMS: Room temp swings excessively. SOLUTIONS: T/S not at fault; check elsewhere T/S wiring hole not plugged; drafts T/S not exposed to circulating air T/S not mounted level (mercury switch types) T/S not properly calibrated T/S exposed to sun, source of heat T/S contacts dirty T/S set point too high T/S set point too low T/S damaged T/S located too near cold air register Break in T/S circuit Heat/Cool Anticipator; System size © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0

END OF Thermostats and Heating Controls © 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.0