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

[SA dude]

noise could also be fan shroud coming loose and being hit by the fan - i had to take my top off and re-do the screws since the plastic broke and the shroud was handing / banging down onto the fan blades.
Also, a noisy fan could indicate that it needs oil. I lost 2 inside fans and just yesterday, the reason that I'm on this site, my outside fan due to lack of oil. Who knew the outside fan needed oil just like the inside fan? haha - i should have known. most sites talk about compressor this and compressor that but oiling the fans has been the number 1 thing that I need. My trane outside unit is 17 years old (thats a long time without extra oiling). My inside unit is now 40 years old (the inside fan is under 5 . also, after that long, and this is not for the faint hearted, you might need to clean the inside coils - mine were pretty clogged up with hair and paper, mold, etc. yuck - yes, they were freezing up and dripping excessively. I did take some pictures but they aint pretty!
thanks for the great article and followup.

[LRHATTON]

Here is my situation. When the fall gets here I have to switch between the heat to a/c quite often. My unit is only 1year and 3 weeks old. Once I switch back and forth a few days in a row, my outside fan unit won't stop running. The thermostate in the house reaches the desired temp, and it will shut off, but the fan outside keeps running. So I tried turning off the thermostate in the house, that didn't work it still keeps running. It has been running for about 4 days now, and I don't know what it is. I had this problem once before, and the contractor that I have my warranty through fixed it, but now it is doing the same thing. Also my labor warranty was up on Sept. 21, 2010. I think he said he replaced the contactor, then, but is it common to have to change a contactor, more than once a year? I really need help, and I have tried to shut the breaker off to it but It comes back on when I flip the breaker back to on.

Thanks, LIla

[Liv]

I'd start with the contactor... Not always but most of the time, it's really simple to diagnose... go out to the outside unit and on the top of the unit at the four corners strike (several times if necessary) the unit with your fist (vertically). If you hear it click and shut off, it's your contactor. A $12 part, if not further investigation is warranted.

[A Person]

It's classic contactor symptoms. The contactor controls the fan and compressor -if both are running even when the thermostat is off then the contactor has stuck closed. It's not normal for the contactor to fail in less than a year, but you could just have a dud - or water could be leaking on to it.

As Liv says - start there and see how it goes

[spence1015]

Heres my situation. AC stops working(inside unit worked and blew warm air, outside unit wouldn't kick on). I replace the cap, nothing. I give the contactor some taps from a hammer and flip the breaker back on and the unit comes on! go through a cycle but next time the inside unit comes on, the outside unit stays off. I went and bought a new contactor and installed, it was different but I am 90% sure everything is where it should be(I'll try getting pics).

Turn everything back on and nothing happens! Now even the inside unit wont turn on. I can turn the outside unit on by manually pressing the coil on the contactor but it won't stay on...and I don't know if the inside unit is kicking on when I'm doing that or not, I'm a one man show for now but my semi-ac-knowledgeable friend may swing by later. Any help is greatly appreciated as I sit here sweating while typing this.

[Liv]

See if you're getting power to the field trigger on the contactor. If not trace back from there.

[spence1015]

I don't have a multimeter...i'll be getting one soon. I just reinstalled the old contactor and it is doing the same thing now(inside won't turn on, outside will if i push in the coil, but won't stay on). What could have happened that would cause the inside unit to stop working? Even when I turn the fan from auto to on, it will not run. Thermostat appears to have no problem.

[spence1015]

I forget to mention I went from a single to dual pole but from what I've read and been told this doesn't matter

[Liv]

I forget to mention I went from a single to dual pole but from what I've read and been told this doesn't matter

My guess, is that information is wrong.... Unless nothing was hooked up to one of the poles.

My guess is something went poof. Possibly crossing low-voltage with high-voltage wires.

I'd start looking at fuses, breakers, and blackened smoky components now. You're really going to have to get a multi-meter to go any further...

...but if you went from a dipole to a uni-pole, I'm betting that's where you went wrong.

[A Person]

I forget to mention I went from a single to dual pole but from what I've read and been told this doesn't matter

It's OK to go from a single to dual pole - but not the other way round. But since it's not triggering the relay, you've wired something up wrong. 90% ain't good enough

Given that it starts when you manually push the contact it sounds as it it's the low voltage activating circuit that's wrong.

Check the contactor label to verify the voltage, have you bought one with a 110v activation coil instead of 24v?

Are you getting 24v at the terminals? A dead transformer or a break in the wires would give the symptoms you describe - as would a dead thermostat.

You will need a multimeter to trace the circuit - and you need to be careful poking around the contactor, 220v will kill you if you're well grounded.

[Liv]

Just realized I read that wrong... thought they went from a double to a single... My bad...

[spence1015]

thanks for your help so far guys, I'm still not making the connection as to what I could have done outside that would make it so the inside unit won't come on. When I get a multimeter I will be checking the 2 smaller gauge wires that hook up to the bottom(for me at least) of the contactor that come out of the building(along with a grd), correct? I'll be looking for 24v there.

I got a 24V contactor, but as of now i reinstalled the old one to see if I could get the inside unit to come on, but I still can't. The thermostat is digital, less than a year old, good batteries, when i turn it to cool i can hear it tick like it always has and it will say cool on, but neither unit comes on.

Thank you

[spence1015]

Are you getting 24v at the terminals? A dead transformer or a break in the wires would give the symptoms you describe - as would a dead thermostat.

You will need a multimeter to trace the circuit - and you need to be careful poking around the contactor, 220v will kill you if you're well grounded.

Sorry, I'm fairly mechanically and electrically inclined(studying Mech Eng), but I'm learning along the way, where is the transformer?

[spence1015]

I just reinstalled the old thermostat and it acted the same as the new one, the new one is now reinstalled.
Did I mention that initially, I knew the contactor was bad because, I gave it a few taps and the whole system worked as it should, and then when I installed the new contactor, I get the issue with the inside unit, I reinstalled the old contactor and the issue persists.

[A Person]

where is the transformer?

Please review this post

viewtopic.php?f=23&t=5931&start=17

You have a problem with the low voltage circuit, either the thermostat is broken, the transformer is broken (or isn't getting power) or there is a fault in the wiring - a bad connection or broken wire.

From what you say the thermostat is OK, you can test that by shorting the Y and RC terminals. You need to find the transformer and verify that it's producing 24V. If it's not verify that it's getting 110V power. If the transformer and the thermostat is working you'll have to check the wiring by verifying continuity.

[spence1015]

Alright, i shorted the Y and R wires, nothing, so thermostat is most likely fine. I just got off the phone with my friend, he said it is likely a transformer problem(keeping my fingers crossed its not the wiring) due to the fact that when i was working on the contactor I ONLY flipped the outdoor breaker for the outdoor unit and NOT the indoor breaker, leaving the 24V circuit on and it most likely grounded out during the process. Likely? Plausible? Definite?

[A Person]

It's quite plausible that during the installation you shorted the leads from the transformer and burned out the winding. Grounding one of them wouldn't be a problem, grounding both would be.

The good news is that a new transformer is in the $10-$20 range and they're readily available

e.g. Lowes



or eBay

[spence1015]

alright, there's an ac supply warehouse on my way to work so I have already picked one up. I'm here until 10 so I'll let you guys know what transpires later tonight, thanks again

[spence1015]

OK, so looking at the old transformer there is a red and brown on top for the secondary circuit, then theres 2 yellow wires attached to one terminal (left) on the bottom, an open terminal in the middle, and a black on the right side, for the primary circuit.

The old transformer has spade connectors(i think thats what they're called) whereas the new one has wires coming out of it, so I'll have to deal with that.

The new one has a red and a green for the secondary circuit. Does it matter which goes to which(red/Brown changed to red/green), for my first attempt I'll be hooking the red to the red and brown to green.

Its got extra wires for different volt levels but I'm going with the 240 the original was 230, next closest is 208. So I'm using the orange(240) and white(COM). The two yellow wires on the old one went to C so i wired them both to the white. The old black one went to 230 so I hooked up the new orange to the old black.

Turn everything back on...nothing, FML. What now?

[A Person]

Normally in the US the transformer takes 110V AC input (primary) and transforms it to 24V AC output (secondary). You are talking about 240V input - are you in a different country?

The principle is the same either way, but that would also explain why you only had a single pole contactor.

The secondary is AC so it really doesn't matter which color goes where. You need to match the primary to whatever your supply voltage is, but while this will affect the secondary volts the actual secondary voltage is not that critical, anything from 20-30v is usually OK

You need a multi-meter to troubleshoot the problem. At the moment you don't know if you have volts on the primary circuit or secondary circuit, or if the low voltage wiring is shorted or broken. Sometimes the low voltage circuit has an in-line fuse.

How about a photo of the transformer and any labels or instructions?

[A Person]

Its got extra wires for different volt levels but I'm going with the 240 the original was 230, next closest is 208. So I'm using the orange(240) and white(COM). The two yellow wires on the old one went to C so i wired them both to the white. The old black one went to 230 so I hooked up the new orange to the old black.

Are you sure white is COM?

White/Rogers, FastStat, NDL Industries and Honeywell all use the same scheme:
Black: Common
White: 120V
Red: 208V
Orange: 240V

[spence1015]

Sometimes the low voltage circuit has an in-line fuse.

BINGO. Blown 5A fuse on the circuit board inside the air handler.

FYI Im in Orlando, FL and yes I'm sure my transformer is 230/240V. Yes I'm sure the white wire was the COM wire, it is a Smart Electric transformer

For tonight I have got it running on the old contactor but the outdoor unit switched on as soon as I adjusted the thermostat. I scrapped some of the corrosion of the contacts with a screwdriver when i had it out, I'll put the new one in tomorrow morning and be sure to flip BOTH circuit breakers.

So essentially I replaced my transformer for nothing because the fuse took the hit. I'm a happy camper though considering I spent about 50 bucks replacing parts that may wear out eventually anyways compared to the $60 that an AC man wanted just to come take a look.

Thanks again Liv and A Person for all your help and knowledge. I hope more DIYers with the same problem stumble upon this.

[Liv]

Yeah!!!!

[A Person]

Well that's good. Having a spare transformer isn't a bad thing. Your old one had an unused center tap on the secondary - that gives you a 12 or 24 output. Might be useful for something.

Interesting that it takes 240V input. I assume that's so that it could be driven from the air conditioner supply line, in which case the whole thing could run from one (paired) breaker

[spence1015]

Well that's good. Having a spare transformer isn't a bad thing. Your old one had an unused center tap on the secondary - that gives you a 12 or 24 output. Might be useful for something.

Actually the unused one was on the primary, for 208V output. I hope I don't have any use for a transformer anytime soon, but I'll hang on to it.
Will I run into any long term problems because I replaced a 230 with a 240?