1. E3 HVACR Controls and Devices
#1 Thermostats and Heating controls

2. 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 v1.1

3. 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 v1.1

4. 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 v1.1

5. 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 v1.1

6. Step-down TransformerL1 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 v1.1

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

8. 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 v1.1

9. Low Voltage Thermostat
The next slide shows 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 v1.1

10. 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 v1.1

11. 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 v1.1

12. 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 v1.1

13. 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 v1.1

14. 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 v1.1

15. 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 v1.1

16. 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 v1.1

17. 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 v1.1

18. 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 v1.1

19. Basic Gas Heating Controls
Three types of controls:
Fan controls
Delay the blower until the heat exchanger is warm
Note: They also delay blower shut down after burners have cycled off
Safety controls
Are only operational when there is a problem
Ignition controls
Are used to start the heating cycle
The next slide shows fan control operation
© 2005 Refrigeration Training Services - E3#1 Thermostats and Heating Controls v1.1

20. Heating Mode – Auto Fan Comp 5 - Fan motor starts on low speed1 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 v1.1

21. Furnace OVERHEATS CompL1 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 v1.1

22. 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 v1.1

23. 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 v1.1

24. 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 v1.1

25. 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 W
Air Switch Proven
HOT
SURFACE
IGNITER-
SENSOR MV
FAN RELAY MV
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 v1.1

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

27. 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 v1.1

28. 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 v1.1

29. 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 v1.1

30. 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 v1.1

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