A/C compressor will not shut off


  #1  
Old 09-10-23, 07:49 PM
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A/C compressor will not shut off

Hvac AC package unit compressor intermittently continues to run after fan shuts off. Produces ice cold air, no frosting of lines, clean filter and coils, fan working at proper speed. The compressor even continues to run after thermostat set to off position, and or regardless of temp in room or temp setting.
 

Last edited by billdakelski; 09-10-23 at 08:24 PM.
  #2  
Old 09-11-23, 04:44 AM
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Is the contactor sticking or is the unit getting a call to run after itís satisfied?
What thermostat?
 
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Old 09-11-23, 05:30 PM
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Thanks for your response. I will check to see if the compressor contactor is sticking. The compressor just stays on regardless of call for cooling or not from the (I was referring to) wall thermostat.
 

Last edited by billdakelski; 09-11-23 at 05:44 PM.
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Old 09-11-23, 06:06 PM
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Have you considered turning off the circuit breaker feeding the compressor so it doesn't just keep running all the time?
 
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Old 09-11-23, 06:10 PM
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The contactor will be closed...... if the compressor is running.
You need to determine if it's shorted/burned closed or if there is 24vac to the coil when there shouldn't be.

More than likely it will be a thermostat issue. To confirm.... pull it off the mounting plate.
 
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Old 09-11-23, 06:15 PM
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Kooter, thanks for your reply. The compressor does not have a dedicated breaker, I shut the unit down immediately when I discovered the fan was not running.
 
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Old 09-11-23, 06:35 PM
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Pjmax, Thanks Ill test the vac from the cap (BTW the cap was just replaced 2 weeks ago). I hope it is just the stat, I will also swap it out to confirm. That would be nice because this beast has defeated 7 technicians in the past, which is why i no longer bother to call them.
 
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Old 09-11-23, 06:42 PM
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compressor does not have a dedicated breaker, I shut the unit down immediately when I discovered the fan was not running.
I presume you pulled the disconnect pullout to shut the power of to the compressor. But, surely you have a C/B that feeds that disconnect pullout and provides overcurrent protection for the compressor, right?...or no?

As Pete said, it appears you either have a contactor in the compressor/condenser cabinet with welded shut (closed) contacts that powers up the compressor continuously or something is amiss with the thermostat that is powering it up continuously.
 
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Old 09-11-23, 07:37 PM
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Kooter, The unit has a breaker in the main box, and a second one by the package unit. Both feed the entire unit. I will check the thermostat and the CC, I greatly appreciate the advice.
 
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Old 09-12-23, 01:04 PM
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update; compressor contractor relay in fried. Any ideas what would be the cause?
 
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Old 09-12-23, 01:30 PM
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update; compressor contractor relay in fried. Any ideas what would be the cause?
It was probably just time for it to expire! It's unlikely the cause was anything related to your compressor or the amperage its contacts were handling or anything else. The coils on those contactors are energized for long periods of time during the summer so they're under a maximum burden.

Sounds like you're all fixed up now!
 
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Old 09-12-23, 09:03 PM
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Typically AC power supply issues cause the contactor to chatter.
That chatter can cause the contacts to arc together.

Most thermostats have time delay protection for AC failure but the problem is that many stats maintain operation even with no system power.

You may want to consider adding a time delay module to your compressor.
It's a simple two wire connection that connects in series with one contactor coil wire.
It's called a "delay on make" timer. Available in many locations. amazon has them too.
delay relay

 
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Old 09-13-23, 08:57 AM
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I am not actually sure the contactor is the problem yet. I am looking for a replacement. When i took the old one off the positive compressor lead looked burnt, and the "plastic" housing broke off a corner, but the contacts work and all wires are making connection. I had a colony of ants in unit a couple of weeks ago, (but not when the event ocoured) and a parts guy said ants can short the relay. There is a dark area on on of the fan board hoping it is ok.
 
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Old 09-13-23, 09:10 AM
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Pjmax, The unit has a basic manual thermostat, I no longer use those battery operated electronic ones with circuit boards and tiny pin connectors. They have cost me a small fortune in time and repair problems.

Would a make/delay timer handle the voltage from the cap? Do I "cut the wire for 240vac" ?
 
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Old 09-13-23, 09:25 AM
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My original contactor was 30 FLA, the one I bought was 40, (did not notice at the time) is that better or should i exchange it for a 30?
 
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Old 09-13-23, 11:24 AM
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My original contactor was 30 FLA, the one I bought was 40
​​​​​​​A 40 amp is perfectly fine - a 60 amp is fine...
 
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Old 09-13-23, 04:09 PM
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Would a make/delay timer handle the voltage from the cap?

Do I "cut the wire for 240vac" shown on the timer?

What time interval should is set?
 
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Old 09-13-23, 10:15 PM
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Insects can become bunched up in the contactor but you can see that.

Same difference with a mechanical thermostat. If the thermostat maintains "cooling on" during a power failure and the power goes on and off..... the contactor jitters/bangs on and off. You don't usually see burned contacts. The contacts just become welded together.

The time delay module goes in the 24VAC line to one of the contactor coil leads.
It doesn't get connected to 240v. Usually 3 minutes is a good setting.
 
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Old 09-14-23, 11:26 AM
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pjmax,
Which is better to attach the timer: Common or H or does it matter?
 
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Old 09-14-23, 04:14 PM
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The 24v circuit is AC so there is no polarity.

Just so we're on the same page.....
...your contactor has L1 and L2 where the incoming power wires connect.
...your contactor has T1 and T2 where the fan and compressor connect.
.... then there are two (possibly double) connections. One on each side of the contactor.

The ones on the side are for the 24v coil power.
One technically goes to incoming C from the thermostat.
The other technically goes to Y/yellow incoming thermostat wire.
You can put the timer in either line. Makes no difference.
 
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Old 09-18-23, 03:46 PM
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Pjmax,
"It's a simple two wire connection that connects in series with one contactor coil wire."

"One technically goes to incoming C from the thermostat.
The other technically goes to Y/yellow incoming thermostat wire.
You can put the timer in either line. Makes no difference."
I am confused, Is it the thermostat wire that goes through the fan board? or the C wire to the capacitor? I already have a make/break unit between the thermostat and the fan board.
 
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Old 09-18-23, 04:00 PM
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It goes in series with one of the 24VAC wires going to the contactor coil (usually the side terminals). Alternatively, you can put it in series with one of the wires where the 24VAC cable coming from the house connects to the internal wiring of the outside unit.
 
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Old 09-18-23, 04:06 PM
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Put the timer board in the yellow Y line from the thermostat inside the house.

The 24v C wire is the C that goes to the thermostat.
The 24v Y wire is the Y that goes to the thermostat.
Yes... they may pass thru the control board.
 
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