I have a Trane XB1000 heat pump. On Monday night, my wife informed me that the upstairs unit in my house was not functioning and the temperature up there was 90 degrees. The downstairs unit was working fine. The air handling fan in the house was working fine. I examined the upstairs outside unit and the fan was not turning. The grill over the motor was very hot so I turned the upstairs unit off at the breaker box and let it cool off. I checked the capacitor with a Fluke 87V multimeter and it check out fine-5 microfarads for the fan side and 58 microfarads on the compressor side.(specs are 5/55 microfarads). I checked the contactor and it was working fine. After letting it cool off completely, I turned the power back on and the unit started up but the fan motor was making a worn bearing noise and the compressor appeared to be working fine. I removed the top grill and the motor and ordered a new motor which my wife will pick up tomorrow- diagnosis worn motor bearings.
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: yes the upstairs unit thermostat was working fine and the filters are clean. We continued to use the downstairs unit which did keep that zone of the house cool. However, today my wife informed me that that unit quit as well. When I got home, I checked the main breaker for that unit-OK. Had 240 V to the power side of the contractor but the relay was not working. However, it did work if I pushed in on the manual switch with a screwdriver- the fan came on normally, sounded good and the compressor seemed to be working fine. I thought it could be the relay so I swapped the relay from the upstairs unit to the downstairs unit and tried it again. Nothing. I of course checked to make sure the thermostat was set at 70 deg(ambient over 90 deg), on cool etc. I then jumped a wire from the yellow thermostat to relay wire on the upstairs unit to the downstairs unit, same with the blue wire and turned on the thermostat upstairs. The relay worked and the compressor and fine both worked. Of course, the upstairs fan went on but not the downstairs air handling fan. So it appears that it is a problem with the low voltage thermostat
circuit- wiring, thermostat or a fuse for the low voltage system for the downstairs unit. My question is- how do I find the low voltage fuse for that unit and how do I test the thermostat?
JA: Do you plan on doing the work yourself?
Customer: Yes. I am quite capable in electronics.
JA: Anything else we should know to help you best?
Customer: I need to know where the low voltage fuse for the thermostat circuit is located so I can check it.
JA: OK. Got it. I'm sending you to a secure page on JustAnswer so you can place the $5 fully-refundable deposit now. While you're filling out that form, I'll tell the HVAC Technician about your situation and then connect you two.