Diy - When Your A/C Won't Stop or Start / Contactor Repair

[dm034]

Thanks for following up. I'm going to work on it this weekend. You did say to turn the power back on when checking the contactor (with an insulated tool) and with the fan and compressor connections detached. So power in this case would be flowing through the contactor (but not the the fan and compressor), which should produce the buzz (if it is the contactor). Right?

[A Person]

Yes, if you disconnect the fan and compressor and still get the buzzing it has to be the contactor

But if you don't get a buzz it could still be a faulty contactor as it may only buzz if it is conducting a current

Sorry if its confusing

[dm034]

Thanks for the helpful tips.

Well, it definitely wasn't the contactor (which was pristine) or the capacitor. It sounds like it's coming from the compressor itself.

That can't be good.

[Some Guy]

My situation is that my A/C fan is running on the outside without any air flow on the inside even when the air is already at the correct temperature inside my home. This has been going on for a few days so the coil is frozen from the condensation in humid Florida. After very little research (one website that was HVAC supply) I decided it was the contactor. I have zero experience with A/C repair and was delighted to find this article. I went home yesterday and banged the top of the unit (where the electrical guts would be) with my fist a couple of times. This didn't work the first time so I went inside regrouped and thought a little about my next course of action; just a breather and a snack before I decided to turn the power off and delve into the scary if not dangerous world of electrical circuitry. I decided to give the old fist wrench another shot at it. I banged (a little harder) on the left, center and right side as I faced my rear exterior wall a couple times in each spot and VOILA! The Fan turned off. Of course I left the A/C on but turned the temp way up and left the fan on auto before doing any of this.

I have no doubt that the contactor will have to be replaced at some point but there is no shame in making a part last a little longer, especially in these times. I just wanted to say thanks for the info and good luck to everyone out there having issues. Don't forget just try hittin' the S-O-B first.

[Liv]

Don't forget just try hittin' the S-O-B first.

That's exactly what happened to mine. We'd wake up in the middle of the night and discover it was like 10F in the house, and I'd run out, half naked to beat on the thing in the middle of the night.

The good news is it's a super cheap, 10 minute fix... if you take your time and are careful.

If you go out and spray it with electrical cleaner (power disconnected of course), it might buy you some time while the contactor is in the mail.

[A Person]

A can of contact cleaner spray would cost more than replacing the contactor

While saving money is fine, remember that an arcing contactor can damage other components - i.e. the fan, capacitor, compressor.

Buy a contactor and replace the once that's clearly on the way out. That way you can do it on your time and not when it's 125 and as humid as a wrestler's jock strap

[J.R.]

I have a Trane BWC024C100CA heat pump, like yours in the demo... The contactor (aka relay) is going bad... The upstairs, inside unit truns on but the outside fan doesn't unless I give it a good "bounce"... Works good, for awhile...
I've been calling around for a new contactor and best price is $82.00 + tax & s/h... I see on other webpages aftermarket contactors for $17.00 to $33.00... Do you know what model/part number my contatcor is ??? Is there an sftermarket product that "fits all" ???

Thank you
j.R.

[Liv]

They're pretty universal. Only differences are a 1 or 2 pole design, and the voltage (110 or 220)

If you have the same unit as I, it can be ordered here for about $15:
http://www1.mscdirect.com/CGI/NNSRIT2?P ... O=24079533

[A Person]

They're pretty universal. Only differences are a 1 or 2 pole design, and the voltage (110 or 220)

and current rating

They are almost always 24v actuated, you can replace a 1 pole with a 2 pole, and you can replace a lower amperage with a higher amperage

So if your current contactor is a 1 pole 20amp, 24v actuated, you can replace it with a 2 pole 30amp 24v actuated contactor.

Look for a part number on the contactor itself. Trane originally installed Seimens Furnas contactors and it's much easier to cross reference contactor part numbers than AC model no.

But this is the most common (if not universal). It's a 30 amp 2 pole. Look at the breaker, if its a 20 amp or 30 amp breaker this is fine. $16 on line

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[A Person]

Oh - and to explain the numbers on the contactor

VAC - volts AC
FLA - Full Load Amperage
LRA - Locked Rotor Amperage
Res Amps - resistive load amps

The contactor can operate load voltages of up to 630 volts AC. The FLA at all voltages is 30A, and the LRA i.e. max startup or stall amperage, varies from 183A at 240V to 110A at 630V.

It's the FLA that's important, usually the LRA is way in excess of your breaker - or even house supply, and it's the surge startup amps that would cause the contactor to melt.

Resistive load amps are relevant if the contactor is driving a resistive load e.g. a water or baseboard heater, rather than an inductive load like a motor or compressor.

I would recommend buying an enclosed contactor like the Siemens one, rather than an open one like the White-Rogers. Ants can get into exposed contacts and although they get vaporised, their carbonised remains make a poor contact and shorten the life of the contactor

Ants aren't quite as bad as mice though

[ziggyff]

a quik novice question: our Central Ac had a single pole 240 volt contactor, 2 main wires on each side of the pole with single 24v leads connected to terminals on one side. However when I got the replacement part, the 24v coil terminals were now on opposite individual sides. I am sure I can get the 4 wires thru the single pole correct but can I screw up the 24v coil connections if i have them reversed? as there are absolutely no way to tell which goes on which side...thanx for any help in advance

[A Person]

No, it doesn't matter which way round the 24v wires are connected

[guirarwanab]

Love it

[laszloapathy]

To atuaseva:
GRRREAT reply! I also have a contactor/relay problem with my Rheem & live in SW Florida. Please tell me via email where you got your part. I need to order ASAP. My email address is: [email protected]
Thank you in advance,
Laszlo

[Liv]

You can buy the part in America through MSC or numerous other suppliers:

http://www1.mscdirect.com/CGI/NNSRIT2?P ... O=24079533