Hello, when I turn the heat on, it starts and heats nicely, but the outside unit is silent and not turning on. However, when I turn the thermostat to cool, it starts nicely, the outside unit. What could be the problem that prevents the outside unit from working (only with heat) and relying 100% on the inside unit for heating.

Some suggested that the thermostat installed does not support heat pump, some said it could be a wiring thing, but I think the problem is more than that as I used to have a thermostat that supported heat pump. A professional in AC came and wanted to replace the thermostat (charging me a lot of $$) just to see if the problem is from thermostat or the outside unit. I figured I ask first before I continue with this. Please help me and tell me what could be happening, and what should I expect if it's not the thermostat.
Your experience is much appreciated.

Thanks!
JM

When tstat is calling for heat, walk out to heatpump listen close to hear any humming coming from the heatpump,, right around where the wire are going into the unit, could be the contactor isn`t getting a signal to kick in,, did it work OK before the tstat was replaced and now not working? If so could be a wireing probablem if you are sure the tstat is the right one for a heatpump

when tstat is calling for heat,,walk out to heatpump listen close to hear any humming coming from the heatpump,,,right around where the wire are going into the unit,,could be the contactor isn`t geting a signal to kick in,,,,,,,,did it work ok before the tstat was replaced and now not working? if so could be a wireing probablem if you are sure the tstat is the right one for a heatpump


Thanks for responding, I am not hearing any sounds coming out of it (complete silence), and I am almost certain that it wasn't working even with the old thermostat. But you mentioned the contactor isn't getting a signal, is that only for heating because if I turn it to cool, it will kick in and work.

Outdoor unit runs in cooling, not in heating? Sounds like you don't have a heat pump thermostat, pardner! What are the terminal designations (letters) on the new stat?