condensor problems

[servicejoe]

I found a bad compressor last week and replaced the condensing unit, but it is now not working. I do not do a whole lot of residential and was wondering if short to ground is the same with 3 phase as opposed to single phase compressors? I have not fully checked out the unit, but the contactor pulls in and will run the condensor fan, but not the compressor. The breaker trips.

[Gunslinger]

Does the evaporator use a TXV? If so, you may need to use a potential relay type starting circuit.

[markettech]

Short to ground is a short to ground - 3 phase, single phase - short is a short.

[coolguysfl]

I found a bad compressor last week and replaced the condensing unit, but it is now not working. I do not do a whole lot of residential and was wondering if short to ground is the same with 3 phase as opposed to single phase compressors? I have not fully checked out the unit, but the contactor pulls in and will run the condensor fan, but not the compressor. The breaker trips.

Joe -I'm sure you're telling the truth, you don't do a lot of residential, --- in fact you clearly don't even work in this industry.

Re-file here as a professional & you'll get lots of help. Until then, call a licensed co. instead of moonlighting before you hurt yourself.

[damedi07]

is the compressor drawing LRA?

[servicejoe]

The breaker trips before it reads any amps, and I have not checked the inrush voltage yet. I am not sure but it may just be a weak breaker.

[servicejoe]

Thanks, I was pretty sure they were the same, But I primarily work on three phase units and I could not remember.

[Jabarco]

I found a bad compressor last week and replaced the condensing unit, but it is now not working. I do not do a whole lot of residential and was wondering if short to ground is the same with 3 phase as opposed to single phase compressors? I have not fully checked out the unit, but the contactor pulls in and will run the condensor fan, but not the compressor. The breaker trips.

Hey Joe,
First, you have to ask the #1 question that every professionally trained air conditioning and refrigeration technician asks. "What killed the first compressor"? Then asks; "What can I do to prevent a repeat failure"?

Then, I want to know;
"Where you going with that gun in your hand"?

http://www.brainerdcompressor.com/_pdf_files/Why2.PDF

[acmech13]

i hope this guy is really in the field or he may have to buy a new system. this isn't gonna be under any kind of warranty if he is not in the buisness. so how did you wire the outside for how many volts?

[skippedover]

There are several things that can cause a circuit break to trip but your question is confusing. Let me explain. You state that only the condenser fan runs but then you also state that the C/B trips before you can get an amp reading on the compressor. Which is it? You haven't stated that you've "wrung out" the compressor windings. If there's a short in theh compressor, you'lll show continuity to ground no matter what the phasing is, one or three. We've had a whole series of problems with Trane TTX and TTZ condensers. Every time we've had C/B trip the problem has been in the crankcase heater. We've even had some condensers that have had sever electrical short circuits and small fires due to the crankcase heater. You could have a C/B that's been weakened by all the tripping but normally that would take a few seconds and not simulate a short to ground, which is instantaneous. The earlier comment about needing a 'hard start' kit with a TXV is also a valid point but again, that wouldn't simulate a short to ground. In that case the compressor would trip on it's internal, thermal overload, which would show as an open 'common' when you wring out the compressor windings.

[acmech13]

how many volts do you have hitting your compressor?

[badbillr]

With power off, check the terminals at the compressor. I have found quite a few units that "tripped" the c/b instantly due to a burnt off terminal that landed on the other "phase" at the compressor terminal box. Note- do not check the voltage at the compressor terminals with the protective cover off, this can be very dangerous. Instead, after checking the condition of the wires and terminals at the compressor and they are good, check the voltage at the contactor where the wires connect on at. Voltage reading should be the same at compressor wires as the incoming voltage coming to the unit. To check if the compressor is shorted, remove the wires from the compressor terminals completely. Place your meter on ohms or even audible continuity will work, place one lead on the copper tubing and scratch the tubing to make sure it has a good connection. Then touch each terminal with the other meter lead, if any of them make the meter sound off or ohms reading is anything other than 0.000 or -.-- ; compressor is shorted

[markettech]

With power off, check the terminals at the compressor. I have found quite a few units that "tripped" the c/b instantly due to a burnt off terminal that landed on the other "phase" at the compressor terminal box. Note- do not check the voltage at the compressor terminals with the protective cover off, this can be very dangerous. Instead, after checking the condition of the wires and terminals at the compressor and they are good, check the voltage at the contactor where the wires connect on at. Voltage reading should be the same at compressor wires as the incoming voltage coming to the unit. To check if the compressor is shorted, remove the wires from the compressor terminals completely. Place your meter on ohms or even audible continuity will work, place one lead on the copper tubing and scratch the tubing to make sure it has a good connection. Then touch each terminal with the other meter lead, if any of them make the meter sound off or ohms reading is anything other than 0.000 or -.-- ; compressor is shorted

Is there a reason in particular to give step-by-step "how to" instruction on a general discussion forum?...........................Just curious:(

[acmech13]

there is no advise from me unless he can answer my questions.

[servicejoe]

The compressor was definately shorted to ground. There was no definate problem found that took the compressor out. All the voltage readings were fine when I checked them. The refrigerant level was also normal. The only thing I did find was, when the compressor was unhooked and the condensor fan was running manually with the contactor pushed in, the condensor fan began to ramp up and down in speed. The amps did not move too much, and I was unable to get a voltage reading. This issue did not repeat itself for further investigation, but I went ahead and replaced the breaker. I am assuming that it was an undervoltage situation on one of the legs of 240 that took out the compressor, or just an issue with the compressor to begin with. The new compressor is running.

[billva]

The new compressor is running.

How about now?:D

Why were you unable to get a voltage reading on the OFM? (Yet, you got an amp reading on the OFM and a voltage reading on the compressor?)

Are you a parts changer?

[Twilly]

Man you guys gave thios new guiy all kinds of help and nobody would help me with my thernostat question

[The Penguin]

whats a thernostat - is that one of them newfangled digithingamabobs?

[the dangling wrangler]

Is there a reason in particular to give step-by-step "how to" instruction on a general discussion forum?...........................Just curious:(

What he said.

[servicejoe]

bilva
I was unable to get a voltage reading on the ofm, because I only have two hands. I was checking amps and holding down the contactor, by the time I let go of the contactor and tryed to get a voltage reading the issue went away. I changed one part on the condensing unit, which was bad. I do not think that qualifies as a "Parts Changer".

[mr horsepower]

how can some of the pro's have the intellegance to work on some decently high-tech and potentially dangerous equipment on an almost daily basis but seemingly cannot either grasp or remember the one or two rules of this site well enough to apply them to their time spent here? specifically the one about NO DIY ADVICE GIVEN ON THIS FORUM. if someone works in the field, they should have no problem achieving pro status. even if the person thats seeking the advice is truly in our field and possibly just minutes away from getting their pro status, that in no way accounts for the entire rest of the world who can also access the information that was just provided. reading something here might be all it takes for some untrained person to apply their new-found knowledge and hurt themselves.