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tsh2 08-04-2009 08:00 PM

Lennox compressor won't stay on
I have a lennox compressor that won't stay on. It is 5 years old and has been fine until this week. It will run for a few minutes but won't stay on as it should. I initially thought there was a problem with the thermostat so I replaced it, but the problem persists. I did mess around with the contactor a little--if you push it in manually, the compressor will kick on. It just won't stay on. As soon as I release pressure on the contactor, the compressor shuts off. I know there is supposed to be 24 volts to the contactor to make the coil pull the contacts in, but I'm not sure which wires to check. There is a wire on either side which come in from the thermostat, but there is no voltage between them at all. I'm not sure which ones to check or what to do next. Can anyone steer me in the right direction from here? Thanks!

tsh2 08-04-2009 08:22 PM

Update: ok, so the wires I need to check must be the ones opposite each other, in the middle on each side... I traced them (small gauge, one red, one white) into the house and to the evaporator. They connect to a switch of some kind which is connected to pvc piping coming out of the evaporator. Don't know if that is a pressure switch or what. I disconnected the wire nuts there to test voltage and the first set of connections tested at about 26 volts. I then took the wire nuts off the second connection and tested those--they were at 26 volts also. In the process of doing this, I pulled the wires apart and had to reconnect them. After I cleaned the wires up and reconnected them, they sparked and the compressor kicked on... So, I went back to the compressor and tested the wires on either side of the contactor and sure enough--26 volts. Those same wires before read 0 volts. Something is going on at the evaporator. Either at that switch or something else that I don't know about. Any input would be greatly appreciated. I'm wondering if this is a low pressure situation and the system needs to be charged or what... Thanks!

tsh2 08-04-2009 08:24 PM

I should add--before disconnecting the wire nuts, I did check voltage at the switch in the end of the pvc pipe and it read 26 volts... Seems like that is the correct reading. The problem may be elsewhere?

kok328 08-05-2009 12:00 PM

Can you post a pic of the switch your referring to?

justt 08-19-2009 07:12 PM

Sounds like you are low on freon which would cause compressor to go "off" on low pressure switch-pressure switch is located inside condensor. Check system charge.

thermalmedics 04-10-2012 10:08 AM

anyone coming across this problem can refer to these videos on low voltage and high voltage troubleshooting at the contactor

you tube vid high voltage

you tube vid - low voltage check at contactor

this will tell you which path to start to head down when troubleshooting

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