Strange internal compressor short.

[ammoniadog]

I have this “Comfort Maker” heat pump/VAV box that I have been working on. It is kind of a wierd unit that runs on 265V. Anyway, when I got to it I found one of the wire burnt off of the compressor (can't remember which one now). I disconnected the remaining two wires from the compressor and started checking resistance. I got 0 ohm's and my meter was buzzing between all three terminals. Since this is a single phase compressor, I thought that this was kind of odd. I condemned the compressor and went to order parts.

The next day a co-worker was sent out to look over the job and double check some things. (He will be helping me replace the compressor). When he checked the resistance he said that C-R and C-S added up to equal R-S like they were supposed to, and that there were no shorts. He thinks the wire may have been loose, and that's why it melted off.

I swear I got zero ohms between all three terminals. After thinking about this a little bit I am wondering if the internal overload might be screwed up and is somehow shorting all of the terminals together when it heats up. Then when the other guy got there it probably reset itself and made everything look normal. Does this sound like a logical theory? I have never heard of an overload doing this before.

I am still kind of new to the trade and to this company, and I am not sure if anyone is going to believe me if my co-worker got it working and can’t find anything wrong. I already went out and ordered about $600 worth of parts and am still waiting to go put them in.

So does my overload theory sound logical to anyone? I will probably go back there to try to force the overload into popping, but in the mean time I am looking for some more insight.

Thanks.

[airworx]

don,t use the buzzer ohm dildo. use the ohms scale.also if your readings were correct breaker would have tripped instantly.

[sonc]

the buzzer ohm dildo?

LOLOL, sounds pretty painful!

You should not tell people how to manage their private affairs

[Edited by sonc on 07-10-2004 at 07:24 AM]

[ammoniadog]

I don't know what airworx is talking about and I'm not sure I want to.

I tried it with the continuity buzzer (actually more of a "beeeeeeeeeeeep") and with it on the regular ohms scale. I was getting zero both ways.

[acjourneyman]

You should have just repaired the wire and tried to fire it off, the worst thing that would have happened is it would have tripped the breaker.A burnt wire is not ususally what happens when a compressor fails,it was most likely a loose connection.I would do the right thing and try the 2.00 repair and cancel the parts you ordered.

[sonc]

Some meters when measuring low resistances (eg. < 10 ohms), it shows no resistance. Buy a better quality meter.

[bjefferson]

Are you sure you got 0 ohms and not OL?Does'nt make sense that you would get those readings.That unit would have been tripping the breaker.I agree that you should have repaired the burnt wire and tried to start the compressor.

[dukester]

Definitely agree with the put the terminal back on and give it a shot with an ammeter hooked up...
Dumb question....did you checked any terminals to ground?
Suspect you missed something if your buddy followed up and had good readings...we're all human...it happens in the heat of the battle....

[wormy]

Had one do this to me once (or twice even)

The insulation material between the terminals was breaking down or something (red rubbery material looked a bit cracked and damp). There was also 'just enough' moisture to give me zero ohms to each terminal and some resistance to ground.

Can't remember if the unit would start up or not....
too long ago

The overload shouldnt' have anything to do with the ohm readings showing short. If it fails, it will fail open and will not close.

[chs]

Dont think you had a short of any kind. I have a "Fluke"(good brand?) meter that is OMH STUPID below 5 omhs resitance.

Try checking the restance of a know working simular compressor. I bet it will read shorted as well.

[bjefferson]

chs
Member

Registered: Jul 2002
Posts: 226


Dont think you had a short of any kind. I have a "Fluke"(good brand?) meter that is OMH STUPID below 5 omhs resitance.

Try checking the restance of a know working simular compressor. I bet it will read shorted as well.


What model Fluke do you have?I have been useing Fluke meters for years.I havent ever had a problem.

[hvacker]

Don't you guys use meggers anymore? I always confirm a short or ??? compressor with a megger.

[Airmechanical]

Don't you guys use meggers anymore?

i totally agree,

this post leads me to believe that we should post a minimum tool list as a sticky thread

moderators what do you think?

we might want to put that in the pro forum!



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