House central AC problem diagnose help ASAP

[Marctrees]

Daughter in Phoenix - Starting yesterday Outdoor unit condenser comp and fan run ALL the time even when T stat not calling for cool.

Furnace blower cycles on and off as normal as per T stat.

Suspecting stuck closed contactor, or something telling contactor to stay closed.

We are going to try to diagnose via Facetime sat eve.

Or Tech will come out Monday.


Question - Can she leave the outdoor condenser unit running for how long ? before opening breaker to let rest ?

Secondly, any other suggestions ?

Marc

 

[Marctrees]

If it does turn out contactor is fried... Looks like generic replacement only $10 at HD ?

Marc

https://www.homedepot.com/p/Noark-4...13144?MERCH=REC-_-pipsem-_-NA-_-300813144-_-N

 

[Marctrees]

Looks like above part says 120 coil voltage.

Is coil voltage normally 120 or 240 on typical 15 yr old home condensor controls ?

Or in fact lo v like 24 off an xformer ?


Looks like HD has both 120 and 24v, so looks like I'll be covered either way.


Trying to learn what I can before I help w this over phone 1k miles away.

Marc

 

[coleman10]

I think what you get depends on the make. Mine are getting toasty, but haven’t gone yet. Picked this one up so I have it on hand for when I need it. Picked up a couple capacitors, too. Prime is quicker than waiting a week for a Home Depot order to arrive.

https://www.amazon.com/dp/B0195UMPNK/?tag=atomicindus08-20

And, yes, it does sound like the contactor is stuck on. If you turn off the power at the breaker, you can remove the cover on the CU and you can inspect the contactor. Make sure not to poke around the capacitor. It still has a charge and will give a nasty shock.

A repair bill for this from an AC company will be around $300, at least that’s how much it would be in SoFL.

 

[Marctrees]

Yup, familiar w the charged caps.

Why do alot of these including the amazon link above say "Single Pole" but sure look like double pole ???????

Don't all single ph 240 v condensor contactors control both legs ?

Marc

 

[Climatecreator]

Some contactors have a leg being energized all the time. I always replace those with double pole. And I'd say 90 percent of the time the coil will be 24v you ALSO have to make sure the amperage is correct. You can use a higher rates contactor but NOT a lower rated.


CC

 

[LS6 Tommy]

Yup, familiar w the charged caps.

Why do alot of these including the amazon link above say "Single Pole" but sure look like double pole ???????

Don't all single ph 240 v condensor contactors control both legs ?

Marc

No. Cheap ones only break on leg, usually L1-T1. L-T2 has a solid buss bar. I usually upgrade when I replace them, too.

Tell your daughter to turn the breaker for het condesning unit off until it gets fixed. Running the condensing unit wtiht the air handler off can cause floodbaclk or slugging.

Tommy

 

[Marctrees]

Ya,, I did tell her to turn off condenser breaker... Here's a cut paste of email update from her -

"Turned the breaker back on after being off for a few hours. Made sure the thermostat was turned off first. The outside unit turned on for a second when I flipped the breaker on, then it shut off on it’s own ( breaker still on). I went inside and turned the thermostat on...unit and blower both turned on as usual. Let it run for about 10 minutes, then turned up the thermostat to see if everything would shut off as normal. Everything did. Maybe the contactor is sticky, but not permanently stuck.

Going to let it run and keep an eye on it. Let me know where you think we should go from here."

So we'll see.

What's the chance of an intermittent sticky contactor ?

Or any other hypothesis here ?

Marc

 

[BD1]

Is it cooling ?? Bad capacitors usually are covered in oil or ugly stuff or have a bulge.
Stuck contactor sometimes is pitted together, a emery paper cleaning works


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[Marctrees]

Cooling fine... caps look fine... only problem was condensor not cycling off.

Marc

 

[LS6 Tommy]

What's the chance of an intermittent sticky contactor ?

Or any other hypothesis here ?

Marc

They do sometimes stick intermittently if they're dirty, loaded with spider webs or other debris. I doubt it would have "healed itseslf" like it did if the contactor "welded".

Tommy

 

[BD1]

The thermostat might be the trouble.
With condenser running, remove one of the 24 volt control wires. If condenser stops, replace thermostat.
It could also mean thermostat is good but relay in furnace is bad. IF it has a relay.
Some are part of main board.


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[bonneyman]

For emergencies, I've popped stuck contactors apart, cleaned them with the striker pad from a book of matches, then blast them out with electronic contact cleaner. Usually gives them a few days till I can get back there with the new part.

If the contacts are covered with fried bug guts then a worn out emery board from the wife (still has enough grit left to work) will clean it off.

 

[Marctrees]

Yup, like filing mechanical ignition points years ago.

Lotta relays are totally or somewhat sealed and can be a Pandora's Box to go in.

But ya, cleaning contacts and spraying out can help... at least temp.

I'll report back in few days history w whazzup.

Marc

 

[Jim greengo]

Contactor on most condensing units is going to have a 24 v coil,not 120v .
Shut the power off to unit,pull cover off to see if contactor is stuck in.

 

[BD1]

Contactor on most condensing units is going to have a 24 v coil,not 120v .

Shut the power off to unit,pull cover off to see if contactor is stuck in.

I think everyone posted 24 volt coil.



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[Jim greengo]

Too much to read late at night.

 

[fitter30]

With the circuit breaker off for the condenser she could look at the contactor to see that is pulled in. Then turn power off to the furnace and see if it opens up or stays closed. This will tell you if its getting power to close or stuck closed. Then if it opens up power furnace back on see if it closes in 5 minutes or right away. If it pulls right in could be shorted stat wiring. Then turn thermostat to the off position to see if it opens up. Opens up could be a bad thermostat.

 

[Marctrees]

So it turns out the contactor was physically sticking.

Points are exposed on it so she sanded them and blew out w can air.

Reports all is good now.

Will still replace part.

Simple fix thankfully.

Thanks for help all !

Marc

 

[rlitman]

Nice job!

Yes, positively replace it. Contactor's contacts have special plating to prevent welding, and now that it's gone (it was gone when it started sticking, and will just erode over time through normal use), it will fail again soon.

 

[JerryC]

Has anybody here used an Emerson Sure Switch?
I bought spare caps and a sure switch when my systems got old.
My spares outlasted the evap coils and I replaced the system before I needed the caps or the ESS.
The new system has a ten year parts warranty so it might be a long time before I try the ESS.

 

[rlitman]

Has anybody here used an Emerson Sure Switch?
I bought spare caps and a sure switch when my systems got old.
My spares outlasted the evap coils and I replaced the system before I needed the caps or the ESS.
The new system has a ten year parts warranty so it might be a long time before I try the ESS.

Never heard of it, but I just looked it up, and will probably be buying a couple for my parent's central air, just as soon as I confirm it will work for them. That looks like a REALLY nice upgrade. Brownout protection and on-delay are great compressor life lengthening features.

Thanks for the tip.