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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 6022
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have 7 wires coming in to my old thermostat. None of them

Customer Question

I have 7 wires coming in to my old thermostat. None of them were marked! I am trying to replace with a new programmable thermostat. On the schematics, there looks like a wire indentified as System XFMR or Heat XFMR...would this be the red wire? This is a heat pump with A/C...
Submitted: 1 year ago.
Category: HVAC
Expert:  airheatman replied 1 year ago.

1. Give me model on units and on new thermostat and this should be pretty simple

2. Can you tell me what are the 7 wires currently going to in unit

Customer: replied 1 year ago.
I don't know they were not mark and I have removed the old thermostat.
Expert:  airheatman replied 1 year ago.

I understand. What we have to do is see what each connects to on other end at air handler. Let me know if you have a control board and what they go to there.(EX red to R, Green to G, etc). If no circuit board give me model on air andler and tell me what color wires each connects to, (EX red from thermostat to red pigtail in air handler, green from thermostat to green pigtail with black stripe in air handler, etc)