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Old 07-03-2020, 04:19 PM   #1
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Compressor not turning on


Hi all -

I will explain the issue, and troubleshooting steps I have taken. Hopefully someone has some advice for me. I am a DIYer (obviously), but have fairly extensive HVAC knowledge (for example, I installed a new system (furnace, compressor, line sets) on my own). Another HVAC unit in my house (r22 1.5 ton) is not working. The outside fan starts up, but no cold air comes out of the vents.

I started with the obvious: checking/replacing the filter, checking/replacing the thermostat battery. Then I checked for 240v and 24v current. Next I placed my Fieldpiece probes on to make sure I had a charge. So far, at this point everything is checking out.

I'll mention that every minute or so, I heard a buzzing noise coming from the compressor. I pulled the disconnect, and checked the capacitor. The capacitor was rusted, so I tried WD-40 and some steel wool to clean it off, but I was not able to get good readings on my multimeter, so I replaced the capacitor. After the capacitor was replaced, the same symptoms were still occurring. Then, I purchased and installed a hard start kit. Still nothing. Then I pulled the top off the fan, took the harness off the compressor and tested the ohms. I read the c+r and c+s = r+s. My readings were not exact, but +/- .5. I assume that was within the margin of error. I also tested for continuity between the compressor harness to the other end by the plunger. Everything tested out with good continuity.

I hope this was clear enough. What am I missing?

Thank you in advance for any help you can provide!

- Aaron
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Old 07-03-2020, 05:01 PM   #2
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Re: Compressor not turning on


Is the compressor running? Or just doing nothing except buzzing? If just buzzing it might be the contactor. I see you checked 240 "current" but did you check to see if you are getting 240v across the compressor wires on the load side of the contactor? Or just the line side?
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Old 07-03-2020, 05:17 PM   #3
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Thank you very much for your reply. The compressor is not running, just buzzing every minute or so (for a few seconds). Someone suggested that the motor might be seized up, and I should try tapping the compressor with a mallet.

Regarding your question: yes, I checked for voltage both where the whip comes in, and also on the other side of the contractor.

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Originally Posted by raylo32 View Post
Is the compressor running? Or just doing nothing except buzzing? If just buzzing it might be the contactor. I see you checked 240 "current" but did you check to see if you are getting 240v across the compressor wires on the load side of the contactor? Or just the line side?
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Old 07-03-2020, 07:41 PM   #4
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Re: Compressor not turning on


Then, yes, it sounds seized up. I've never dealt with that particular issue in my DIY experience but my guess is that it's done.

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Originally Posted by aharonhakohen View Post
Thank you very much for your reply. The compressor is not running, just buzzing every minute or so (for a few seconds). Someone suggested that the motor might be seized up, and I should try tapping the compressor with a mallet.

Regarding your question: yes, I checked for voltage both where the whip comes in, and also on the other side of the contractor.
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Old 07-03-2020, 07:46 PM   #5
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Re: Compressor not turning on


Test the capacitor (both) to verify the one was faulty and the new one is good. I’ve had dead ones out of the box.
Verify it’s the correct capacitor and it’s wired right.
Check amp draw when it’s trying to run. May be pulling LRA.
If it still doesn’t run it’s likely locked up.
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