Lennox AC HS24-651-1P

[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.

[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.