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HVAC Tstats

Understanding Thermostats. HVAC Tstats. Thermostats are the central control for HVAC systems. HVAC Tstats. HVAC Technicians must know: How to Thermostats operate How to wire them How to troubleshoot them. HVAC Tstats. Basic heating thermostat R- is voltage input from 24v transformer

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HVAC Tstats

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  1. Understanding Thermostats HVACTstats

  2. Thermostats are the central control for HVAC systems HVACTstats

  3. HVAC Technicians must know: How to Thermostats operate How to wire them How to troubleshoot them HVACTstats

  4. Basic heating thermostat R- is voltage input from 24v transformer W- is heating output to signal heating system to turn on Heat anticipator can be adjusted and is energized when thermostat temperature sensor is calling for heat HVACTstats

  5. Basic Cooling thermostat Y- is cooling output to signal cooling system to turn on G- is fan output to signal indoor fan/blower to start Cooling anticipator is a fixed resistor energized when thermostat temperature sensor is not calling for cooling HVACTstats

  6. Basic heat/cool thermostat Some thermostats will have “off” as a mode HVACTstats

  7. Basic heat/cool thermostat with isolating sub-base Some thermostats will have RH + RC terminal to isolate transformers from the heating unit and the cooling unit HVACTstats

  8. 2 stage cooling thermostat with single stage heat Y1- is first stage cooling, normally 1 of 2 compressors Y2- is second stage or second compressor Y2 is internally warmer than Y1 by about 2 degrees F HVACTstats

  9. 2 stage heat/cool thermostat W1- is first stage of heating, example 1st bank of 2 banks electric heaters or low side of 2 pressure gas valve W2- is second stage, second electric heater or high pressure side of 2 pressure gas valve HVACTstats

  10. Heat pump thermostat O- is output signal when selector switch is moved to cool B- is output signal when selector switch is moved to heat HVACTstats

  11. Heat pump with emergency heat When selector switch is moved to emergency heat Y is no longer energized as first stage Back up heat is now first stage Emergency heat light is on to indicate selector switch was moved and compressor is off HVACTstats

  12. Basic heat/cool thermostat wired to oil primary control HVACTstats

  13. Basic heat/cool thermostat wired to oil primary control with A/C option HVACTstats

  14. Basic heat/cool thermostat wired to Gas furnace control HVACTstats

  15. Basic cooling thermostat wired to A/C controls HVACTstats

  16. Basic heating/cooling thermostat with isolating sub-base wired to oil primary and A/C controls Note both systems have their own transformers HVACTstats

  17. 2 Stage cooling 1 Stage heat thermostat wired to Heating and A/C controls HVACTstats

  18. 2 Stage cooling 2 Stage heat thermostat wired to Heating and A/C controls HVACTstats

  19. Basic Heat pump Thermostat with “B” and “O” terminal wired to Heat pump controls HVACTstats

  20. Heat pump Thermostat with Supplemental and Emergency Heat lights wired to Heat pump controls Supplemental light is on when ever second stage heat is on Emergency light is on when mode switch is moved to Emergency heat HVACTstats

  21. With power on to both systems a volt meter should read the switches Top meter reads 24v because the heat sensor is open HVACTstats Troubleshooting

  22. With power on to both systems a volt meter should read the switches Middle meter reads 24v because the cool sensor is open HVACTstats Troubleshooting

  23. With power on to both systems a volt meter should read the switches Bottom meter reads 0v because the fan switch is set to “ON” Jumping out “R” to “?” should start the controlled unit or system NEVER SHORT “R” TO GROUND HVACTstats Troubleshooting

  24. Electronic thermostats “Can” have set back programming options Allowing different temperature for different times during the day These thermostats save energy by raising or lowering the temperature when a building is not being use HVACTstats

  25. Thermostats are switches that open and close by temperature Different thermostats are need for different applications Wiring is simple if you know the color/terminal codes Troubleshooting is done much like checking switches NEVER SHORT “R” TO GROUND !!!!!!! HVACTstats Review

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