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Posted By: ThinkGood In-Wall A/C Compressor Won't Turn Off - 07/11/03 12:43 AM
I have a through-the-wall air conditioner, 220V, digital settings.

It started misbehaving when I tried to turn it off (by pressing the big red ON/OFF button).

The compressor still runs even though the display indicates that the unit is off.

I pulled the plug immediately--naturally, that shut the compressor. I left the unit unplugged for a few hours and tried again with the same results.

Any ideas as to what is wrong with the thing?

From the little I know about this stuff, if that compressor runs and the rest of the unit doesn't, the compressor will burn out...
Posted By: Trumpy Re: In-Wall A/C Compressor Won't Turn Off - 07/11/03 01:31 AM
Just at a guess, mate,
I'd say that the Compressor contactor has welded closed, this happens a bit.
Hope this helps. [Linked Image]
Posted By: ThinkGood Re: In-Wall A/C Compressor Won't Turn Off - 07/11/03 01:35 AM
Ouch...
Posted By: NJwirenut Re: In-Wall A/C Compressor Won't Turn Off - 07/11/03 01:36 AM
Definitely sounds like the control device for the compressor has failed in the ON position.

Usually, these are fairly large mechanical relays, subject to the usual contact welding problems, but I have seen one unit which used solid state relays, in which the output device (SCRs or TRIAC) failed by short-circuiting.

Either way, it sounds like you will need to change a relay.
Posted By: ThinkGood Re: In-Wall A/C Compressor Won't Turn Off - 07/11/03 02:17 AM
The unit was here when we bought the house...there is a second 220V unit that was here (both of these are Carrier brand, no more than 5 years old) that stopped cooling about 2 years ago.

I guess it's time for some more fans [Linked Image]
Posted By: Trumpy Re: In-Wall A/C Compressor Won't Turn Off - 07/11/03 10:21 AM
ThinkGood,
I work quite often with the Carrier brand of Air Con equipment, if you need a hand fault-finding the unit, let us know! [Linked Image].
The company I work for over here, is a Service Agent for these units and I've fixed HEAPS of them.
That larger unit, you mentioned, sounds like it's lost it's gas (Refrigerant), my guess is there will be a small leak in the system (which is easily repaired!), the main cost would be in re-charging the system.
But, sometimes it can just be cheaper and easier to replace the units, if they are getting on in years.

[This message has been edited by Trumpy (edited 07-11-2003).]
Posted By: ThinkGood Re: In-Wall A/C Compressor Won't Turn Off - 07/11/03 11:36 PM
Could this component be the culprit?

OMRON
G4A-1A
24 VDC
20A 250VA
Posted By: Trumpy Re: In-Wall A/C Compressor Won't Turn Off - 07/12/03 12:34 AM
More than likely, mate.
You could try disconnecting it from the unit and bench-testing it, with a 24V PSU.
The contactor should open and close as normal and this can be confirmed by hooking it up to an ohm-meter while applying the 24V to the coil.
If the meter reads a dead short with the supply ON and OFF, the contactor is shot.
I probably shouldn't have to say this, but mark the wiring sequence of the contactor BEFORE you remove the wires, Compressors don't take too kindly to reverse polarity!.
Hope this helps, I would imagine you'd be wanting to get the Air Con running again, I saw on the BBC weather report, last
night that temperatures are certainly getting up there in the US!. [Linked Image]

[This message has been edited by Trumpy (edited 07-11-2003).]
Posted By: NJwirenut Re: In-Wall A/C Compressor Won't Turn Off - 07/12/03 01:05 AM
That definitely sounds like it. Have replaced a lot of those nasty little things in A/Cs and microwaves. Contact welding is the usual failure mode, often evidenced by melting of the plastic case around one or both of the contact terminals.

There should be no continuity between the 2 top terminals unless there is power applied to the coil. If an ohmmeter check shows welded contacts, you can buy a new one for about $6 from Mouser Electronics:
http://www.mouser.com/catalog/613/580.pdf

Your relay is down at the bottom of the page.
Posted By: Trumpy Re: In-Wall A/C Compressor Won't Turn Off - 07/12/03 02:22 AM
Gidday there Bob,
Since parallel importing started over here, in 2000, I've seen heaps of Contactors and CB's with Brand-names of reputable manufacturers on them, only to turn them over and find something like "Made in Pakistan" on them.
This is just not right!, it's blatant commercial plagiarism and judging by the number of faulty and just plain rubbish products,I've had to replace since then, a real blot on the good name(built up over years) of these manufacturers. [Linked Image]
Posted By: ThinkGood Re: In-Wall A/C Compressor Won't Turn Off - 07/14/03 02:20 AM
It works! It works!
[Linked Image from 65.108.216.53]


I did mistakenly reverse the leads on the relay, and the unit was completely dead. I expected the worst, put them back properly, and it's working OK now!

Thanks for the help.
Posted By: ThinkGood Re: In-Wall A/C Compressor Won't Turn Off - 08/14/03 01:01 PM
Well, it started again. The compressor wouldn't turn off. Fortunately, I was able to fix again, by reversing the leads on the relay, switching on the breaker, switching off the breaker, reversing the leads back and it was OK.

With the unit unplugged, when testing the relay, I had a reading of 24VDC which slowly crept downward.

I would like to replace the whole circuit board--the power leads unplug very easily so it should be easy enough to do. Now to find a source for one...any ideas?

[This message has been edited by ThinkGood (edited 08-14-2003).]
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