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

[Liv]

It's bloody hot out there. It really sucks when the A/C doesn't work right. Getting it fixed can be expensive if you call the HVAC people & I don't understand how Lowes and Home Depot have tons of Do-it-yourself stuff, but when it comes to home heating and air conditioning they have nothing.

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You would think we all had nuclear reactors sitting in our backyards, with technology so incredibly complicated that the average person could never understand. The truth is it isn't. In fact, every A/C unit out there generally has the same basic parts that make up the unit. Many of which can be replaced by the average person. HVAC people don't want to tell you this, but one of the most popular parts to fail is the electrical contactor.

I've put this repair off for about 3 years, each year I go out and bend, or modify the 18 year old electrical contactor just to get us by. This year it was finally time to replace it. It's actually really simple, and the symptoms of a bad contactor are usually that of an outdoor compressor unit continuing to run after the indoor thermostat is shut off. Other symptoms are the A/C unit not coming on, anal leakage, and a erection lasting more than 4 hours.

A contactor or relay is an electrical device that takes a control signal usually 12 volts DC, 24, 120, 208-230 volts ac and creates a magnetic field to pull in a set of contacts that controls another device that may or may not get its electrical power from the same circuit. Note: 99% of most control circuits are 24 volts AC.

Now here is where things get sticky. You take the top of your heat-pump or A/C unit and find the contactor. You can see the bronze terminals are firmly soldered to the contacts even when you shut the circuit breaker off. The bronze stuff is what keeps the contactor from welding itself shut, and when that wears down, the contactor fails.

You call your HVAC neighbor who wants $150.00 to repair it, and you look up on the Internet how much a part is and they want about $50.00. Or you can just buy it from where the Air Conditioning repair guys get it and pay $10.00.

First look on the coil of the contactor and find it's voltage. Most have stickers, but mine didn't. The voltage should be labelled around the copper wound magnet. If your unsure, almost every major brand home A/C & Heat Pump unit uses a 24 Volt 30 Amp 2 Pole Contactor which can be ordered here for $13.57.

Careful when touching the terminals. Often the the capacitors are still charged and can give you a nice 24volt shock even if the power is cut. I would tell you how to avoid this, but that wouldn't be much fun, now would it?

My new electrical contactor replacement came in less than 2 days, via UPS to the house from MSC's distribution warehouse in Pennsylvania.

Run outside with the bad boy and screw the wires in matching the old positions to the new contactor. Don't be shocked if the contactor looks different. My original 18 year old contactor was definitely "outdated".

While I had the top of the A/C unit off, I pulled the sides of the unit and did some preventive maintenance by cleaning off the leaves, dust, and dog hair on the coil that has been decreasing efficiency and using more electricity.

How to replace a Electo-Magnetic Contactor:

1) Stare and gawk at how an 18 Year old Trane Heat-pump that's never been serviced, still runs.

"Snow Trane" we call her.

2) Rip the top off. It's usually just a few screws holding it on:

Trane Heat Pump Cover Removed

3) Find the Contactor. Diagnose, and replace:

New Electrical Contactor

(There's the new one installed. Much cleaner then the old one... and it works!)

4) Take old Contactor and throw at neighbor's chicken:

Old Broken Contactor

5) Go inside and enjoy the cool A/C with the knowledge you don't have to run outside in the middle of the night and smack the unit to get it to shut off!

[caramichele]

Girl, you rock. Informative and amusing.

[dieguito9999]

Liv, thanks for the info on replacing the contractor on the AC, there's isn't much more information out there about this seemingly nuclear/atomic/rocket scientist task, and AC techs want to charge me $260 to do it. I bought the 24 VAC contactor from the online source you mentioned in your posting (MSC Ind Supply), cut off the power, and opened my 2 year old Rheen Corsair unit to attempt to replace it. I swallowed as I uncovered the old contactor knowing that it might not look like the new one, which in fact it didn't. It does however, resemble the new one light years more than your old one resembled the new one as per your photos.

My question is, the old contactor is blocked by another piece with wires going to it that I can't seem to pry lose without breaking it, and the screws that hold the old contactor in place are covered by that piece. In addition, there appear to be additional contacts on the old contactor that have wires going to them, I have no idea where to connect them. Any light you might be able to shed on this?

[Liv]

Without looking at it, it's tough to say how to remove the screws. All I can say, is someone had to put it in, so it has to come out somehow. It may involve removing other parts to get to it. As far as the contactor, does it look like this?

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If so, then what you've got is a single pole contactor with an addition solid post... that's okay, because you can use a dipole contactor in leu of it. Basically what you've got to remember is a contactor in nothing more than a switch. A single pole contactor is one switch. A Di-pole contactor is two switches. So on and so forth. Basically the 24 volts enters one of the small wires and plugs into a connector on the coil. The coil magnetizes, and pulls the contactor close and now the 110volts or 220volts of electricity can pass through the switch.

If you've got a single pole like the one above, then the one side is merely a bar of metal which is always on, the other side is the switch. As long as Rheem didn't require high voltage on 24/7, which I doubt it does... you can merely put the wires on the unswitched side, and build a small jumper wire to that pole of the contactor to activate it.

You definitely want to take pictures in case you screw up, but it should be a fairly straight forward swap. At worst you might need to get some connectors to make the old wires fit the new block, although my contactor had little metal prongs that unscrewed and could be reattached on the new contactor. A cheap $10.00 voltage meter might be your friend, and you'd still come out on top. If you haven't taken the old one off yet, I'd suggest get to that point, take some pictures, and then just transfer each screw of wires at a time. You might find those extra wires all get attached easier then you think. I thought I'd have to redo the ends, but it ended up, the prongs were transferable.

Now I say this only doing it once, and not having any knowledge in the a/c business, but it's probably impossible to screw this up, so I wouldn't worry too much.... When I say impossible, I mean unlikely... when I say unlikely, I mean... do this on a cold day.

But... as long as the 110V leads stay on their respective poles, and don't touch the 24 volt leads that go to the coil on the contactor, then practically any combination of insanity will bring about some sort of function. Just do screw for screw, bolt for bolt... have pictures as a backup and lots of water to drink as you sweat over the thing.

Post a picture for an attachment, and I'll scribble all over it for you.

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[atuaseva]

I change my contactors every spring and fall and at the same time thoroughly clean the unit. I'm in SW Florida and it doesn't miss a beat. I get my contactors, 2 at a time (Honeywell 2 pole 24 volt) for $7.30 a set. $7 shipping comes to $21.60 2 sets delivered. 5 minutes of your time saves you $150-$250. Of course all you Wall Street bailout recipients of my tax dollars can just have your service tech replace them because you probably wouldn't know where to start.

[Winslow]

Very informative and entertaining. This is possibly the best DIY I have ever seen or used. Great job!

[M Jordan]

Had ac people at our house yesterday and was told it was the contactor -- they want $601 to replace it -- seems pretty steep doesn't it????

[Liv]

Had ac people at our house yesterday and was told it was the contactor -- they want $601 to replace it -- seems pretty steep doesn't it????

Unless the contactor is connected to a gold brick... or your a/c unit is on an isle surrounded by a moat with gators, then yeah it's steep.... it's a $10 part, less than 1 hour labor....

[ackeepsrunninghouston]

Long story...asked someone to come out and check the duct work when my husband was home. The guy shows up 2 hours late and explains he can't do it because it's raining outside??? It had just begun to drizzle but the ducts, of course, are in the attic. He also has that heavy cologne over lingering alcohol from a wet lunch smell. We send him away, "Yeah, your right, it's raining." Trying not to waste a whole other day off for my husband I have someone out on a Wednesday at 3:00 to check the duct work. He came very highly recommended. "Oh, sure, why don't a do your summer service check while I'm at it, it will save you money in the long haul." Foolish me, I fell for it...........I say sure, the Trane Clean Effects needs to be cleaned before it gets to hot to get up there to do it, so okay, let's do the checkup and also clean the Clean Effects unit. Highly recommended guy comes out, checks the freon, declares the Clean Effects doesn't really need to be cleaned (sure, we should wait until August on this!!!) , tells me that everything about our fresh air intake is wrong, putzes around in the attic a bit, comes down and tells me that the duct work is leaking everywhere, all up and down the line and that it will be about $250.00 a vent to replace plus some other $75.00 per vent plus some other stuff. He leaves and the air conditioner never, never goes off until 1 am. It was working fine before he came! I'm laying in bed imagining him going along the ductwork (the old metal type) and give a good push downward in an opportune place or two. The poor husband comes home the next day and goes up in the attic to find that, indeed, the ductwork had been tampered with. Looks like there was some prior issues that were massively capitalized on. In the meantime, he makes the repairs (the very thing I was trying to have him avoid doing do to overwork, overage, etc). Finally, the big problem now; ever since the "crook" came and messed around in my attic, the air conditioner continues to run even when the temperature hits the set point on the thermostat. Fool me, can't believe I let him touch anything. He checked the freon outside, removed a panel and hosed (with water) down the unit outside. He messed around with my programmable thermostat and was in the attic untended. I'm reasonably sure that he turned the fresh air intake up extra high which we reset. I've since had the freon rechecked by someone I trust. The freon is good. We set the humidity level up higher just in case that was triggering a problem (never did before). Adjusted the fresh air intake down a bit more and the ac still hits its set temperature and keeps running for hours. This contact that you guys are replacing. Do you think that might have been tampered with or that taking the water hose to the 5 year old Trane unit with the service panel removed might have caused the problem? Right now, the problem here is that I tried to make life easier on my husband and made a big mess out of things; he stuck his leg through the hall ceiling tonight and I know it was because it was speaking to me from the attic and was distracted. Glad I can still distract my husband after 34 years, but would appreciate any input as to why the ac keeps running even when the house is at the right temperature. Thank you

[Liv]

Yep sounds like the contactor, and I imagine the water didn't help, though I'm not a chemistry major I'm not sure how 220v and wet copper would react. My guess is it could atleast rust a tad bit and shut the contacts, either way these things do go out... so you probably would have eventually had a problem anyhow, it's just this guy may have helped it along.

To get you by, try turning on the a/c and when it won't shut off try striking the four corners of the a/c unit on top with a hard strike of your fist. It usually will shut off then, and you'll know it's the contactor.

[Guest]

It turns out this past winter I had a bad contactor (but didn't know) and kept on using the fuse box to turn on the heat. Now the outside unit will not start. When I take off the electrical cover I came hear a small humming from the contactor. Will replacing the contactor get my AC back running?

[Liv]

It turns out this past winter I had a bad contactor (but didn't know) and kept on using the fuse box to turn on the heat. Now the outside unit will not start. When I take off the electrical cover I came hear a small humming from the contactor. Will replacing the contactor get my AC back running?

No way to know for sure, it's worth a shot though as cheap and easy as they are to replace.

[A Person]

There is a way to tell. The contactor is a relay (the low voltage from the thermostat operates a coil that switches on the high voltage compressor) and can fail in one of three ways. The high voltage contacts can fuse together and the air conditioning will run continuously (most common); or the low voltage coil can either short internally or burn out and the AC won't start

The first is easy to diagnose - but that isn't your problem.

You can test the coil if you have a multimeter that can measure resistance (in Ohms) You need to shut off the power to the unit, remove one wire from the low voltage terminal and measure the resistance between the two low voltage terminals. It should be around 20 Ohms. If it's less than 10 Ohms the coil is shorting, if it's more than 30, it's burnt out.

Or you could just replace the contactor anyway, but you'll be annoyed if it turns out to be the compressor and you have to replace the whole unit.

[Liv]

There is a way to tell.

Well I know that... I figured it was easier for them to order a $10 part and replace it with a phillips screwdriver than buy a $10 multimeter, learn how to use it, then buy a part, try that, and still find out it's bricked.

You could of course throw caution to the wind and bypass the contactor with two screwdrivers and see what happens... please film if you do, it could get real interesting real quick though...

[Guest]

Here's a good one for you . . . my unit froze over in Florida in late June, both inside evaporator and outside condenser/compressor unit. When I removed the panel and found the CONTACTOR it looked like melted black plastic around the contacts, but, closer inspection revealed it was ANTS, they were trying to build a nest around the contactor and they had been "fried" by the current and were fouling the contact not allowing it to open. A quick shot of contact cleaner and compressed air and it looked brand new!

[need more help]

I have replaced the contactor with success. my unit will not go on unless I puch in the magnet. what can I do now?
please help

[Liv]

If it's coming on when you pushing on it then the solenoid isn't getting voltage on the trigger lead. Find that lead and start tracing it backwards would be my first guess... you'll probably end up at some weird end of a micro controller I imagine which then goes into your thermostat. All you can do is do a visual check or with a meter check for voltage going in and out of whatever it leads you to. Since you'd probably have to call a HVAC person if it's some sort of internal part, you might want to just call a HVAC. Then again you might want to just skip all that and try to check the thermostat out... See if your getting voltage to engage the solenoid.

[A Person]

You will need a multimeter and be comfortable using it on 110 v circuits before try what follows. If not - pay the AC man

The ac is controlled by the low voltage circuit, which consists of a 24V transformer connected via the thermostat to the contactor.

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Safe bit - there are no high voltages in the thermostat
Remove the thermostat and look at the back you will see a terminal marked RC and one marked Y. Disconnect the RC wire and check the voltage between it and the Y wire - it should be between 20 - 30v. If you have the right voltage connect the RC wire to the Y wire - the AC should start, if it does the thermostat is faulty ($50 - $100 fix), if not then you still have a problem with the contactor

If you have 0v you have a fault in the low voltage circuit - either the transformer is faulty or you have a break in the circuit.

The transformer is usually attached to the breaker panel and looks something like this:



Dangerous bit - you are dealing with 110v

you should see 110V on the input leads and 20-30v on the output. If there is no 110v on the input - check the breaker. If there is 110v on the input but no volts on the output, the transformer is faulty ($25 - $50)

[A Person]

FYI the terminals on a thermostat are labelled as follows

RH - From the 24VAC transformer on the heating side
RC - From the 24VAC transformer on the air-conditioning side
W - To the relay that turns on the heating
Y - To the relay that turns on the AC
G - To the relay that turns on the fan.

The heating and cooling circuits are separate but each is like the diagram above. Sometimes they share a transformer in which case RH and RC are jumpered together

[depaky]

We just had service performed on our 2 AC units. The technician replaced the capasitor and contactor in both units (up/down AC), as well as added freon to each. The Furnaces checked out perfect. The heating and AC in my home is 11 years old. The cost for service was approx, 600$ for parts and 228$ for a service aggreement for both units (Spring/fall service). The next day the upstairs unit went out. They came back and looked at the furnaces first. He determined that a transformer had blown. He replaced the transformer and installed a fuse so the transformer would not blow again. He then tried to turn on the AC unit. After the system booted (5 min) the single to the blower did not happen and the system shut down again.

The technician went outside to see if a faulty contactor had been installed, or installed incorrectly. He found the contactor was not working properly and replaced it. The technician tried to start the system back up again, and it still failed. The technician began testing wires and determined that a wire running from the furnace, down the wall to the outside units, was shorted. He said we need a new wire installed and called the office to arrange it.

The AC company provided and estimate of 6-700$ to do the wiring. They said the short was not caused by anything they did, it just happened. Any thoughts? Not sure where to go from here.

[Liv]

I'd get a second opinion IMO at the very least.

[A Person]

From your description, it sounds as if the thermostat wire has a short that overloaded the transformer. $600 sounds like a lot to replace that. The wire is $20 and an hour's labor would be about right.

[Help]

Can the contactor cause the outside unit to make a loud, rattling noise? Our unit sits right outside of our bedroom window and when the fan comes on, it makes a loud rattling noise, then stops when the fan turns off.

[A Person]

No

If the unit comes on and stays on the contactor is working. If it rattles it's because something is loose. It could be a loose fan, or worn bearings. It could be the compressor, which would be expensive.

[Liv]

My bet is the compressor... I heard our neighbors go out in Arizona... was so darn annoying.... Sounding like the brick in the clothes washer