yet another "broken A/C" thread

Have you physically checked the control voltage on the contactor though? Not where the wires that are going to it begin, but at the actual contactor.
 
Is the return path (common) for the contactor good?

Also just because voltage to contactor is good doesn’t necessarily mean it has enough amps to keep it pulled in.

You haven’t replaced the transformer yet right? And if you push the contactor manually the compressor starts?
 
awheelterd said:
Have you physically checked the control voltage on the contactor though? Not where the wires that are going to it begin, but at the actual contactor.
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ponykilr said:
Is the return path (common) for the contactor good?

Also just because voltage to contactor is good doesn’t necessarily mean it has enough amps to keep it pulled in.

You haven’t replaced the transformer yet right? And if you push the contactor manually the compressor starts?
Click to expand...
OK so I re-checked. It was really late at night and I was blurry.
The contactor sits and clicks about once a minute, maybe two.
Measuring at the contactor itself, it is 0 except while it clicks, then it spikes up and immediately back to 0.only read tiny voltage but I suspect thats the refresh on the screen not keeping up with teh rise and fall time.
There is a little board between the constant 26v coming in from stat control and the contactor. I'm guessing this is a timer that makes it try every few minutes.
Contactor ground is solid.
Have not replaced the transformer yet.

If I push in the contactor it, works. Spins up just fine.

And to top it all off, this morning I went out to recheck everything again, pluggedt he fuse it, and it magically spun up like it should. So at the moment it is running to get the house cooled down.
While running - input leads on the contactor measure 24.2v.

Got a guy that is going to come by this afternoon. His thinking is that little board may be bad.
 
Your unit shouldn't have a defrost board, maybe it's a compressor lockout sensing board? You can just bypass all of that and tie the yellow wire straight to the hot side of the contactor coil and see if that turns the unit on when stat is calling for cool, you'll just be bypassing any high or low pressure safeties. Post a pic of the condenser. If it's still having the issue you might have a bad transformer.
 
Well... it's cycled 3 times this morning... and worked fine every time. I haven't done or changed anything....
 
Well, worked fine all day. Guy came by and said, we'll if it ain't broke, I can't really fix anything.

An hour later, it quit again (well, didn't start)

There's a short cycle timer board before the switch. Bypassed it.
Low and behold - Runs right off the feed from the stat.

Measured the output from the timer board... yup its 24v, but when on the contactor it dies nothing. I suspect something is funky in it snd can't supply enough current to pull the contactor.

20210629_161003.jpg
 
RatLabGuy said:
Well, worked fine all day. Guy came by and said, we'll if it ain't broke, I can't really fix anything.

An hour later, it quit again (well, didn't start)

There's a short cycle timer board before the switch. Bypassed it.
Low and behold - Runs right off the feed from the stat.

Measured the output from the timer board... yup its 24v, but when on the contactor it dies nothing. I suspect something is funky in it snd can't supply enough current to pull the contactor.

View attachment 350950
Click to expand...
That’s what I was getting at in a previous post. Voltage can read correctly with not enough current to operate. Example would be a wire cut in two except for a couple of strands.

I think you’ve found the culprit.
 
ponykilr said:
That’s what I was getting at in a previous post. Voltage can read correctly with not enough current to operate. Example would be a wire cut in two except for a couple of strands.

I think you’ve found the culprit.
Click to expand...
yep. bypass it.. I have seen those fail before. I'd u look at the back of that board u may see an overheated spot. pretty common.
 
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