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Is my compressor dead?

3K views 44 replies 8 participants last post by  beenthere 
#1 ·
Well, I think I know the answer so kind of looking for an affirmation or some small miracle that I overlooked something :).

So a relative of mine had HVAC problems with no cool. They called a tech out and he said the condenser (outdoor) unit compressor is dead and needs to be replaced.

Skeptical that a 5 year old unit would die like this (given how common compressor failure misdiagnoses is) I went to check it out for myself.

The symptom is, the condenser immediately trips the breaker whenever cool is called for. Just trips over and over again every time it is reset.

When I get there to look at it, I noticed the suction line insulation going into the unit is soaked (I mean soaked) in refrigeration oil.... 1st thought was uh-oh leak somehere in these brazed joints.

The capacitor(s) "looked" fine in that it wasn't exploded or bulging.

To cut to the chase, disconnected the leads running to the compressor (verified with the schematic) and measured the resistance....

This is what I got:

56 ohms between the start and run winding.....
56.5 ohms between the start and common.
.8 ohms between the run and common.

The .8 ohms suggests it is fried......

Yes/No?

Did I miss anything?


Thanks......
 
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#6 · (Edited)
check resistance between each pin and the compressor case.

if u get anything but open it's shorted to ground.

the refrigerant oil suggests a leak.

5 year old unit is worth replacing a compressor on, just make sure the cause of failure is rectified. I don't know what if anything can cause a compressor to short, just that it happens

would want the unit checked for leaks, bad capacitor, acid.

would want a new filter drier.
 
#7 ·
I will try and get out there to test that short to ground but given the resistance I got on the run coil and the breaker immediately tripping, what else could it be? Would a faulty run capacitor cause this? Could the resistance legitimately be .5 ohm (my leads are .3 ohms themselves)?
 
#8 ·
yes, if there's a short inside between those terminals, damaged insulation?

a short somewhere in the unit will do it.

condenser fan motor, wire damaged, touching the case.
 
#9 ·
0.8ohms is close enough to av dead short to me. (i call it phase to phase short as opposed to phase to ground) He mentioned that he disconnected the leads so that rules out the rest of the unit for that resistance. I would condemn that compressor too. If the unit was registered it should be under warranty. (You'll have to pay for labour though) It sounds like you have a major leak, and with it running with a lack of refrigerant caused the windings to break down. That will have to be repaired too. (A nitrogen purge and a new filter drier is highly recommended)

At 0.8 ohms, for a moment that compressor would draw 300A. (not accounting for sag and other electrical characteristics, at 240vac) That would trip breaker even if it was only a split second. (before inductance plays a part)

Cheers!
 
#11 ·
Unless there's something wrong with unit or system which killed the compressor, replacement compressor should last many years. less wasteful too for those who care.

Could also do a condenser-only change-out.
 
#12 ·
Unless there's something wrong with unit or system which killed the compressor, replacement compressor should last many years. less wasteful too for those who care.

Original compressor should have lasted a lot longer then 5 years, but didn't. If a new one is installed, and the cause is not found. Then the OP gets to pay for a new compressor plus all cost of changing it out if the compressor goes again after the 1 year part only warranty. Very wasteful of the OP's money.

Could also do a condenser-only change-out.
Condenser only change out is an option. OP would get a 5 year warranty on the new condenser's compressor at least.
 
#14 ·
I'm going to see if I can get at the terminals on the compressor itself to test the winding (if it has one).....but barring something extraordinary like a worn wire shorting to ground, something shorting the terminals at the compressor etc... looks like it is dead.

Been thinking about just replacing the compressor but it is somewhere around 5-6 years old so reversing valve could give out (heat pump), electronics etc.. etc.. so even if it is a bit cheaper it may be penny wise and pound foolish.

I just wish I looked at it earlier, the insulation soaked in oil would be a tell tale sign of a problem before the compressor died.
 
#16 ·
a matter of personal preference, i hate the throw-away society. what ever happened to a piece of equipment lasting 30 years?

5 years is nothing. better efficiency, but it gets offset by repairs and high labour costs.
 
#17 ·
a matter of personal preference, i hate the throw-away society. what ever happened to a piece of equipment lasting 30 years?

Unfortunately, American society happened. People wanted things for less, but they also want paid more for their labor at their jobs at the same time. So manufacturers had to cut cost to pay higher wages and sell their products at a cheaper price, which meant/means using lower quality parts, and often having a low standard of quality control.

5 years is nothing. better efficiency, but it gets offset by repairs and high labour costs.
As a rule. If it was installed properly. Then it will last a long time. More then long enough to see/realize a ROI.
 
#18 ·
As a rule, i push my customers to change the reversing valve at the same time. It's only an extra hour and whatever the valve cost is. Other companies will be different though.

We've changed enough, and had reversing valves stick in less then a few months. (usually found on testing after recharging.) The windings will be breaking down. The resulting crud and carbonised oil from the arcing inside will plug the little pilot tubes on the reversing valve.

Cheers!
 
#19 ·
Yeah, its a real bite if you change out a compressor on a heat pump, and then find out the RV isn't working. And was the cause of the compressor failure.
 
#20 ·
Unfortunately, American society happened. People wanted things for less, but they also want paid more for their labor at their jobs at the same time. So manufacturers had to cut cost to pay higher wages and sell their products at a cheaper price, which meant/means using lower quality parts, and often having a low standard of quality control.


Don't forget the corps maxing profit for their shareholders and the reasons why people need to be paid more and buying things for less in the first place -> aka inflation, especially in housing costs, health care, education. (all three turned into major rackets)

crony-capitalist rackets happened, big government & big business screwing people over

but i digress.
 
#21 ·
No. It come down to. The more you make, the more you want. The more you want, the more you need to make. So people ended up wanting more for less. Big business had to cut corners to fill the consumer demand for lower prices. And employees demands for higher wages.

So the OP will be able to get a new system for less then it would cost, if the equipment was designed to last 30 to 40 years. Because the general public doesn't want to pay the price for that type of quality.
 
#22 ·
Ok folks we're thru the looking glass :)

So per the suggestions here I went over and decided to make extra sure it is dead.

I looked down inside (didn't for some reason yesterday) and the wires seemed good, not cracked or touching etc.... also noticed it was a copeland scroll; not an expert but as I understand, scrolls are way more reliable than reciprocating (esp when losing oil)....... so even more skeptical of actual failure....... I figured what the hell, let's take the top off, pull the connector on the compressor and test the resistance right at the pins.

To much surprise and delight, the windings were not shorted.... hmmm, so sprayed some contact cleaner on there put the connector on then went to the panel side where the wire harness connect to the contactor etc...

Again, pulled off the 3 wires - 2 from the contactor one from the capacitor.


Measured the resistance the exact same way as yesterday and here's what I got...

run to start winding = 830 ohms.
common to start = 520 ohms.
common to run = 315 ohms...

So all those number add up right. But the RLA is listed at 17 amps (LRA is 96.7) so ohms law calc doesn't seem to make sense.

So tried to start it up again... this time it tried to start the compressor a bit before blowing the fuse.

The HVAC tech that came out reported that the capacitor was shot. I didn't have a meter with capacitance to test to verify.


Any thoughts on what in the world is going on here? Bad wire harness?
I am guessing the capacitor problem would cause the problem I am seeing now.

Plan is to replace that capacitor(s) and slap on a 5-2-1 hard start kit and try to fire her up again.

Thoughts?


(seeing why compressor failure is so easily misdiagnosed now :) ).
 
#23 ·
OHMs law is for resistance loads. A motor is an induction load, so it doesn't apply.

OHM readings are way to high. But trying a new run cap and a hard start won't hurt anything.
 
#25 ·
The compressor is shot if u're measuring between the winding and ground rather than using the wrong terminology.

Resistance to ground = electricity flowing to ground. Should be open circuit, no exceptions.

Dangerous too with the pipes/cabinet potentially being energized.

Don't waste your time with a capacitor, time for a new compressor or new outdoor unit.
 
#26 ·
Sounds like you got a molten mess for windings. But why not, the system is already nuked, no difference now in trying a new cap if that's what you want. I would have condemned that thing with either measurement. (ofc, assuming that you're measuring the way we believe you are. I've seen apprentices...and some mechanics do interesting things.... Lol)

The ohmic reading would be close to the LRA rating. (the windings aren't great inductors if the rotor isn't spinning) The FLA is the highest amperage that some engineer designed the windings to handle while being cooled by the refrigerant. Only relevant when it's actually running.

Cheers!
 
#27 ·
yah, what happens in the motor is that the magnetic field produced by magnetized moving rotor induces back voltage in the windings which opposes flow of electric current.

ohm's law is pretty much only good for electric elements.

Even light bulbs read very low resistance when off, resistance changes when on. (not for the same reason, that's a heat thing)
 
#30 ·
Do not waste your money on a capacitor, a bad cap will never cause the breaker to trip, only the internal thermal overload to open each time the compressor tries to start.

if it's actually a burnout you would be better off changing the entire outdoor unit along with the indoor metering device.

It's dead.
 
#29 · (Edited)
If it lost all the freon and froze up and damaged the scrolls or slugged all the oil out or overheated from no freon to cool the compressor it could be literally burnt out. The tech should do a acid test on the old oil from the burnt compressor B4 replacing it. If it has acid then you need to flush it with RX11 and put a suction line filter drier on along with a new liquid line filter drier.
 
#32 ·
short aside...the internal protection if working should trip b4 the breaker.

i still think it's dead with the readings posted.
 
#33 ·
Good chance it is. But why have someone 4 years down the road read this thread, and replace a compressor due to a shorting cap because you said they can't trip the breaker. When indeed they can and do.
 
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#34 ·
beenthere said:
Actually, many a bad cap has tripped a breaker. The capacitor can short to case, just like a compressor can.
I've seen a few units trip because of bad caps. Couldn't tell you how many. Also I have seen the breaker trip because they are just plain weak (the breaker). I have also seen them trip with a bad capacitor with the breaker being rated very low or close to the value it was suppose to be. Just didn't care to argue the point. Thanks for bringing it up
 
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