Basic Question, I feel dumb asking

[coolerguy]

Had a call on an old Carrier RTU about 2 weeks ago, don't know the model # its about 5 ton, built about 1983. Problem was a welded contactor, no big deal, changed it out all checked out. I installed a 30 amp contactor compressor running around 15 amps RLA. Didn't think much about it, this week I get a call, find the contactor I installed totally trashed, the bar and spring between the points laying in the bottom of the panel and points melted to the point of nothing left. The other pole was fine (2 pole contactor), this time I installed a 40 amp square D, mega ohm compressor, its good, power is clean (least while I was there). Thermostat is a digital Honeywell that has a time delay, so I know noone is jamming it off and on. 24 volts coming back on Y1 and 24v @ coil. It does has A CLO card that works, economizer is bypassed because owner does not want to spend the money to fix it, so we know the economizer has no control over compressor, for what its worth..Suggestions please ?

[dandyme]

HP,AC, or gas pak?

30a seems kinda light

what was start up A?

[grayghost]

single or three phase ? What did disconnect forks look like ? Is time delay the last device before contactor coil?

[HJ Controls]

did you check start and run amps, wouldn't hurt to make sure your not flooding and check wiring from contactor to compressor.

[ScottBeck]

Does it have a saftey board on it? The low and high presure switch and one leg of the compressor goes through a current sensor. I have seen those boards short cycle power the the contactor. Its hard to catch unless you are there when it happens

[Sun Dog]

One pole fried...., other not....Sounds like Scott may have a likely cause-don't think I've seen one quite like that....

[XcelTech]

I have been getting a rash of bad contactors recently. They run for a week or two then the coils get weak and start chattering. I am actually replacing one on Tuesday. I got two from Trane on brand new DX systems and one from Baker Dist. (all three replaced at no extra cost or hassle Thank you to both companies) all this month. Might be a common coil maker being used by several contactor companies. Copper is getting expensive you know.

[pdrake65]

Possilbe bad contactor coil as previously stated. I might be concerned about installing a 40 amp where a 30 amp ran for years without issue. Could cause more damage than just a contactor.

[mcewans]

Possilbe bad contactor coil as previously stated. I might be concerned about installing a 40 amp where a 30 amp ran for years without issue. Could cause more damage than just a contactor.

This should not be an issue as long as you have the proper sized circuit breaker/fuse installed upstream of the contactor.

[pdrake65]

This should not be an issue as long as you have the proper sized circuit breaker/fuse installed upstream of the contactor.

Maybe I should clarify my line of thinking with a question to Coolerguy. Did you put a 40 amp in because you didn't have a 30 amp or did you feel that the unit was drawing more amps than the 30 amp could handle and that was the cause for the meltdown?

[ascj]

Have you tested the CLO?

Pull low voltage off term 3. CLO should trip. Check by measuring 24v across term X and term 1. Then put wire back on term 3 and check voltage at term 3 and term 1.

[ms64]

In the past I installed a voltage recorder

[boilerman856]

If it is 3phase wouldnt a voltage imbalance cause this? Just an idea.