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AT HVAC Experts - A question?

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cardiac

cardiac

Platinum Member
I have a 6 year old Goodman gas furnace - Goodman A/C unit (Model # CLT18A) with a Honeywell digital thermostat. The outside A/C unit/compressor will not shut off unless I throw the circuit breaker. It cools just fine. But when the thermostat calls for it to cycle off, the furnace/blower shuts off but the outside A/C unit continues to run. I let it go for 30 minutes before I shut the breaker off. If I turn the thermostat from A/C to off, it still continued to run.

Is the contactor unit stuck closed? Shouldn't all power to the outside unit be shut off if the thermostat is set to "Off"? Bad thermostat?

It is under warranty for a few more years (10 year warranty), but it is parts only. If it is the contactor, I'd like to change it myself, saving the labor costs.

Thanks a bunch,

Bob
 
If the thermo is set to OFF, the AC unit should not be receiving a closed relay condition for the contactor to energize.
So yes, it sounds like your contactor is sticking closed.

A contactor replacement is very easy and cheap to do yourself.
You can get a contactor for $10 and it should be held in with 2 screws, plus the power line set screws.

To make sure it's not the thermo, I would totally disconnect it from the control wires at the wall while the AC unit is running. Then see if it continues to run. There is a chance the thermo relay is sticking closed or the logic is jacked up.

Also, AC units will stay on for some time after the call for cool is off... but 30min. is excessive.
 
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Power outside is always on. Your thermostat controls a relay that opens and closes the "switch" for the high voltage that runs the AC..

If it were me, i would open up the side of the unit and whack it with a mallet while its running to see if it will toggle.
 
Thanks guys!

Edro, that is why I let it run for 30 minutes. I know they do cycle, but I thought that was excessive, too.

Olds, kinda the way I am leaning.

Jaha, thanks for that info. I was not sure if the unit had power to it at all times. I guess it should, as I have a knife switch to shut it off right next to the outside unit....

I think I am going to try and disconnect the thermostat first, then pull open the outside unit if that doesn't work. I am comfortable doing that...

Thanks folks!!
 
i just had this problem on my unit. Replace the relay (contactor) in the outside unit.
they are usually about $20, but you need to order it by part number.

http://www.northamericahvac.com/servlet/StoreFront
I ordered mine online, because most of my local shops will only sell parts to contractors, (not to customers)...YMMV

while your in there, check your capacitor for expansion, or maybe consider ordering a spare... They are useful to have on hand as well.
 
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I see you do have a digital thermostat, you should just be able to yank it off the wall away from the base plate while its running to check that. At least thats how mine is installed.

If you turn the breaker back on does the ac unit just turn on then?

I would disconnect the thermostat with the breaker off, go down stairs and turn the breaker on. If the AC turns on, your relay is stuck.
 
Pulled the Y wire off the thermostat, flipped the breaker, and the compressor started up. Took the cover off the outside unit, found the contactor, sprayed a little electrical contact cleaner on it, tapped it with a rubber mallet a few times, and it has worked fine since. I'll pick up a new contactor as I guess this one is on it's last leg....

It's gonna be 97 here today (93 already), so the AC is gonna get a workout.

Thanks for all the help, guys!!

Bob
 
sao123 said:
i just had this problem on my unit. Replace the relay (contactor) in the outside unit.
they are usually about $20, but you need to order it by part number.

http://www.northamericahvac.com/servlet/StoreFront
I ordered mine online, because most of my local shops will only sell parts to contractors, (not to customers)...YMMV

while your in there, check your capacitor for expansion, or maybe consider ordering a spare... They are useful to have on hand as well.
Click to expand...



FYI if you bring cash and know what you want then the local shops will sell to you.


If you come in asking questions while waving your amex around they'll show you the door.
 
Most HVAC contractors will sell you parts you won't get it under warranty but there cheap. Don't let the outside unit run with the fan off your indoor coil can freeze up and send liquid freon back to the compressor. You can't compress a liquid...
 
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