We decided to change the thermostat of our heat pump/air conditionnning unit. First 3 images are the old unit. The first 3 wires(1 and 2 picture) yellow red orange were not connected to anything, just hanging in the wall. the 4 image is the new thermostat. Now the problem I have is that my system doesn't cool only hot air comes out.If I put back the old thermostat everything works fine. reason why I believe the problem is my wiring? robertshaw thermostat robertshaw  thermostat

old york thermostat new thermostat honeywell rth 8500

1 and 2 are robertshaw 10-529 temperature sensor/ 3 is old york thermostat/ and 4 is the new thermostat honeywell rth 8500

1 Answer 1


I found the solution by playing with it. On the new thermostat, remove the blue and grey wires, as they are just relays to the temperature sensor. Black goes to C, and link E and AUX. In the thermostat settings, go to option 170 and change it to option 2 for heat-pump settings. This process did the trick for me.

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