30 replies to this topic

[klawleman]

Going back over things, I am certain of what my meter reads but not clear on what the readings me. I thought that if I read any resistance between a compressor terminal and ground it was a dead short, but looking at what ACtechGUY posted is a reading of nearly 4 Million ohms acceptable but a reading in the thousands or lower it is dead.

Now take an OHM reading from each wire to ground( Ground is any clean peice of metal attached to the chasis like a screw) . You should have a very high resistance ( IN THE MILLION OF ohmS) . If you have thousands or lower resistance , the compressor is internally shorted to ground (FAILED, DEAD , DECEASED, GONE PECAN, KAPUT........)?

Moreover, when I first measured with the Klein, it occasionally and momentarily picked up the 4 million ohms, but I thought it was a false reading caused by me momentarily touching something. Whatever, the readings are not now momentary and are the same measured at the disconnected wires into the control box or when taken direct from the condensor (I earlier mistakenly posted "capacitor") terminals.

I wonder if one of the windings was pretty well shot and when I hooked up a new run capacitor it or they further deteriorated to the point that the short is readily masured on the Klein. My cheap pocket digital still cannot measure it.

Edited by klawleman, 14 August 2011 - 12:26 AM.

[ACtechGUY]

Before I believe you always said it looked like a short in a winding. Given these new readings, does that now appear pretty definitiely the case?

Those resistance readings don't really concern me too much. they look somewhat normal. And they almost never exactly add up to a nice pretty equal number (probably due to a bad connection between the compressor screws or pins and the meter leads)

Casing w paint scraped off or copper piping to any one of the three terminals reads 4.95 MΩ. (My old cheap pocket meter still reads infinity.)

The reading in the millions of OHMs to ground is also pretty normal. Maybe a little on the low side .
It could be that it is still grounded . And that ground shows up when power is applied to the compressor.

The meter should be manually set to "manual" (not the default auto-ranging)
I don't know if that's a good meter to read less that 10 OHMs ..

I personally have used fluke meters for the last 15 years, and not one of the 5 flukes I have had(lost or rained on or stolen) have had a "manual" mode . They have always been autoranging , and darn reliable. The leads when shorted together read about .6 ohms. Klawleman's meter may just have a auto zero mode to "avoid confusing the user" with the meter lead resistance.

[klawleman]

I remetered without any attempt today to start the critter. I was thinking that readings might be altered if I tried to start. I do not see where they changed with the possible exception of my readings from crank case to windings.

One possible source of confusion was eliminated, which is which winding was being measured, by the fact that each terminal is marked C, S, or R.

My measurements from YESTERDAY were:
C to S: 2.7 Ω (fluctuates as low as 2.6 and as high as 2.8)
C to R: 3.3 or 3.4 Ω
S to R: 4.6 or 4.7 Ω


My measurements from TODAY were all taken after installing fresh batteries.

The Klein MM1000
C to S: 2.7 to 2.8 Ω
C to R: 3.1 Ω
S to R: 4.4 to 4.5 Ω

Old pocket GE (after deducting the .6Ω read when touching probes:
(Manually set to 200 Ω range)
C to S: 2.7 Ω
C to R: 3.2 Ω
S to R: 4.5 Ω

I checked to ensure that polarity did not change the results (reversing the red and blackk probes).

Reversing the probes SIGNIFICANTLY CHANGED the resistance when I ohmed the terminals to the crank case. When the Black probe was on the crank case and the red on any terminal the reading would continue to slowly rise, but measurements began at 4.5 MΩ and slowly climbed above 5 MΩ. Reversing the probes elicited readings of 14 MΩ to 15MΩ. TRIPLE! I don't know whether or not this indicates anything to you folk, but IIRC ACtechGUY posted that the reading I took yesterday was a little light. That was just under 5 MΩ, which was what I still get today with black probing ground and red probing the terminal.

Edited by klawleman, 15 August 2011 - 02:21 AM.

[ACtechGUY]

I suggest you try to test to ground at the contactor once again , with the new meter . maybe disconnnect the crankcase heater totally and try to restart the unit.

Maybe only have the compressor in the circuit and try to restart.

Maybe try to replace breaker that trips , just in case of a bad breaker.

Last option . buy a new unit...

[klawleman]

I suggest you try to test to ground at the contactor once again , with the new meter . maybe disconnnect the crankcase heater totally and try to restart the unit.

Maybe only have the compressor in the circuit and try to restart.

Maybe try to replace breaker that trips , just in case of a bad breaker.

Last option . buy a new unit...

I have done all that except trying a new breaker. I did swap the wires out to a 40 Amp breaker on the board and it popped, but it is possible that a good 50 amp, which is what is on that line, won't pop. Given the cost of a new system is about $6K, it is worth investing in a new breaker and I will pick one up tomorrow. Thanks again.

Re buying a new unit, I have had three contactors out as it looks like that is where this is heading.

Edited by klawleman, 20 August 2011 - 01:00 AM.

[klawleman]

I suggest you try to test to ground at the contactor once again , with the new meter . maybe disconnnect the crankcase heater totally and try to restart the unit.

Maybe only have the compressor in the circuit and try to restart.

Maybe try to replace breaker that trips , just in case of a bad breaker.

Last option . buy a new unit...

I am not sure how to test the contqctor to grund, but I isolated it by removing all wires connected to terminals and probed each terminal to the grounding lug. No resistance. Measuring from one coil terminal to the other, I got 9 ohms. If I measure from the load side to the grounding lug I get no resistance. The contacts are burnt but they open and close. Even when the CB pops the contacts remain closed until the thermostat control is turned from cool to off.

I disconnected the crankcase heater. I tried this earlier and the results were the same. No difference.

Earlier I tried swapping the load lines from the 50 A breaker to the next largest one I had on the board, a 40, and it made no differnce. Still, it was possible that a good 50 might handle what a good 40 could not and I got one from the HD. It still popped with a new 50 Amp.

I ascertained by trial and error that it only pops if both the Black wire from L-1 is connected to the common terminal of the compressor and the Red wire from L-2 is connected to the Run compressor terminal. If either is disconnected from their respective contacter load terminals, nothing pops. I take that to mean that the short is in the run winding.

The circuit breaker opens if the yellow lead to the start winding is disconnected, but common and run terminals are still connected. If the yellow is connected but either the common or the run terminal is disconnected the cb still does not open. I may be misinterpreting this, but this suggests to me that the start winding is good but the run winding is shorted.

One thing that I don't understand is why I don't hear a humm from the start winding trying to do something, even if by itself it cannot start a compressor. Perhpas there is a delay before the start winding kicks in and the thing shorts before that can happen. It is immediate.

As for replacing it, I contacted a 4th contractor, actually Home Depot who will have one of its contractors call me.

[klawleman]

I should have asked how do I test the contactor. What I have done is to ohm between all contacts to ground and the other contacts, and everything was an open circuit. (The exception being a reading of about 8 ohms across the coil, not from either coil contact to ground.)

As for violtage readings, I haven't attempted to take any with the entire system energized. With everything disconnected, except the load lines to poles 1 and 2, I got readings within a couple of tenths of 120 V at each. (contacts open)

On the load side I got .021 V on L1 and .027 for L2. (contacts were open)As miniscule as a reading of 2/100 or 3/100 volts may be, could that likely be a direct short when a start up load is pulled across those contacts?

[RegUS_PatOff]

maybe disconnect only the Compressor and re-try the Circuit Breaker ...

[klawleman]

I already figured out that the breaker didn't pop unless both the leads to the common and run terminals of the compressor were connected to the two load sides of the contactor. To rule out any possibility of the contactor being the problem, I just got done using wire nuts to directly connect the same compressor leads directly to the lines from the house and the breaker popped. I replaced the breaker, which felt mushy and was no longer difinitely opening, with a new one and it popped wide open. I suppose that rules out a short in the contactor being the problem.

Nothing else was hooked into the circuit; neither capacitor, the contactor, the fan motor, the crnaksaxe heater, or the potential relay. Nothing.

[ACtechGUY]

Kudos for trying everything in an effort NOT to buy a new A/C. It was clear a while back that you were doomed. We all have to learn the hard way...............

By the way if you abuse a circuit breaker enough... ...AND YOU DID !!! . It WILL fail..

It is clear that you either live somewhere where it is not REALLY hot or you done got yerself 'A BIG 'OL HOUSE' and this system serves an area that you maybe don't use much.

If neither of the above are true then I suggest investing in the highest SEER A/C you can buy . Electricity is not getting any cheaper from now on.

Good Luck, Because all brands suck or break in one way or another.

Edited by ACtechGUY, 21 August 2011 - 09:39 PM.

[klawleman]

You got it. It is a pretty big house but it gets pretty hot here. Fortunately it is low humidity. What saved us is the 4 ceiling fans I installed a couple of years back. Thanks for the help. At least I know I didn't pass an opportunity to ressurect the old thing from the dead. You may have a point about buying a higher SEER rating. Electrical is just going to get more expensive the same as gasoline. Anyway, thanks again.