Problems with A/C: fan and compressor not starting

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Old 08-16-15, 02:02 PM
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Problems with A/C: fan and compressor not starting

This thread helped me a good deal. My unit also is doing the same thing, where inside fan is working, but outside compressor and fan will not kick on.

After following the thread, I was able to determine:

-240 V to the unit is
-24v is passing through both sides of the connector

If I manually depress the connector, the fan and compressor come on. So I believe this means the coil is good. I only have a single wire going into the connector which ties right into the thermostat cables, so no timer in the mix.

From all of this, I believe I am dealing with a bad connector.

SO, as always the case, this happened on a sunday with no supply stores open, etc.

Maybe a silly question, but is there any particular harm in overriding the connector to get the unit working again, and pulling power to the unit when the house is back to temp (basically just trying to get the house down from 85 degrees back to mid 70's.) I appreciate I need to stay on top of it and pull the power to avoid the lines freezing, etc. Just wasn't sure if there was anything else I should be aware of to make this bad idea.

Thanks,

John


Separated from.... http://www.doityourself.com/forum/ai...t-turning.html
 

Last edited by PJmax; 08-18-15 at 07:14 PM. Reason: started new thread
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Old 08-18-15, 08:04 AM
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I presume you have it fixed by now but I wouldn't suggest doing what you propose. You would have to pay very close attention to catch it when the fan on the air handler shut off. Sorry for the slow reply. I just got notification of your post this morning.
 
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Old 08-18-15, 03:27 PM
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I had set the thermostat to 65 to keep it running to not run into the situation where the inside fan would shut off. I manually have been switching the breaker to the AC unit before we went to bed, and only left it on a few hours in the AM to keep the house at a reasonable temp.

So here is the weird part....

I went to the local Supply store and purchased two contactors. The first one did not work for whatever reason, although like I mentioned above, I am getting 26v across both wires to pull the contact down. I installed the second one and the contactor worked right away.

10 minutes after installing it, the contactor pop'd up again and wouldn't pull back down.

I reached out to my local HVAC guy, he said it is certainly the contactor and offered up another one for me to try (as the supply store was now closed), I installed this one and it worked to cool the house and through the night into the next morning. Came home from work today and the house was in the mid 80's and upon checking the contactor, the buttons were lifted and I had 26v on both sides.

I am quite confused on what is going on at this point, as it seems as simple of a device as they come, there is voltage across the magnet, and 240 coming in. nothing else at play (no timer, etc). How could I possibly install 3 defective contactors?

I am lost at this point..... HVAC guy is on his way now, although he seems just as stumped as me.
 
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Old 08-18-15, 07:09 PM
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10 minutes after installing it, the contactor pop'd up again and wouldn't pull back down.
Did you check for 24vac when the contactor would not close. You probably didn't and if you did you would probably not find it there. There is a good chance you are low on refrigerant as the low pressure safety switch would keep the contactor from closing on its own.

Holding the contactor in to run the compressor and fan is not a good idea. If you ARE low on refrigerant you can damage the compressor.

-24v is passing through both sides of the connector
If I manually depress the connector, the fan and compressor come on. So I believe this means the coil is good
If you have 24vac to the contactor terminals and the contactor does not close.... the coil is BAD.
 
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Old 08-24-15, 08:59 AM
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just wanted to follow up.

I had an HVAC guy come out and checked my heater and expressed concern of the t-stat cable going from the heater to the AC unit possibly having a break. I replaced the wire and still had the issue.

I started to 'wiggle' the wires on the control board and started to see the lights flickering, which indicated the AC unit was switching on and off. I seemed to locate the culprit which was the tstat terminals on the control board being loose. I ended up taking the board off and noticed a cracked soldier joint and re-soldered it, all seems fine now.

after understanding now how the contactor works, I can state that I was testing it incorrectly. I was using my tester with the ground on the AC unit, not testing positive negative across the contactor. I was indeed getting 26v across, but that makes sense if the common was on.

I am looking to replace the entire unit anyway, so I am opting to ride out the board repair until I properly replace the system.

Thanks again for the assistance, I appreciate it!

John


... I should point out that the connection seemed inconsistent, as the HVAC guy did show me the 26 vold at the control board when he tested it, so just a loose connection
 
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Old 08-24-15, 09:19 AM
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Thanks for stopping back and leaving us an update.
 
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