1988 Trane compressor contactor switch sticking on - likely cause?


Old 08-09-19, 12:35 AM
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1988 Trane compressor contactor switch sticking on - likely cause?

I discovered the compressor contactor switch isn't releasing when the air handler is turning off and the compressor continues to run. Unit is from 1988. It otherwise works fine, provides plenty of cooling.

I turned off the juice at the circuit breakers and popped the top off and found cobwebs everywhere around the circuit board, capacitors and contactor switch - vacuumed it off and found the contactor stuck in the On/Closed position. The spring that applies pressure is still intact. Worked it by hand a few times, vacuumed off the unit, it seemed to be working freely again and seemed to be turning off with the air handler but it started doing it again. I've got it turned off at the circuit breaker. I don't think it's a matter of the magnet not turning off, it doesn't want to stay closed once I've jiggled it with my fingers.

My next step is to pull it and give it an off-unit inspection and cleaning.

Any suggestions for what I should be looking for? Is it typical for these to need replacing? My assumption is it's a matter of the switch simply sticking due to wear and/or debris but I wonder if there's something else that could be going on that's outside the scope of my awareness.

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Old 08-09-19, 04:58 AM
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Everything wears out eventually. I think I would take the $50 gamble and just replace it. You've certainly gotten your money's worth out of the unit.
Old 08-09-19, 05:06 PM
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As a follow-up the contacts were fried and it was sticking due to arcing fusing them together enough to keep them from opening when the power to the magnet was cut. The "weld" was weak enough that a light flick of the finger broke the bond.

Going to a local electrical supply house they didn't have the exact same unit but the guy sold me a Noark 2-pole contactor with appropriate ratings and the guy explained where the corresponding line and trip connectors were. I had the foresight to take pics of where all the connectors were on the old unit before disconnecting them and quadruple-verified I had everything on the correct side of the contacts. Fired it up and as far as I can tell it's working fine. I don't detect any issues at the outside unit and it turns on and off with the inside unit.

It appears to be fixed.
Old 08-09-19, 05:11 PM
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Your lucky the unit is still running....... never mind the contactor.... at 31 years in service.
There are dozens of replacement contactors that can do the job.
As long as you picked one of the same amperage duty you'll be fine.
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