AC issues, please confirm my diagnosis

[masraum]

The AC has been running fine, no problems with keeping the house cool. Tonight I came home and it was warm. I noticed that the fan was on, but the air coming out wasn't cool. I then noticed that the outdoor unit wasn't running.

I checked the power to the unit and see 240V. If I turn the AC off, wait a bit and then turn it on, I get a loud buzz from the outdoor unit for a couple minutes, but it doesn't run (neither the compressor nor the fan on the compressor).

Based on some reading on the Internet, it sounds like it may be a bad capacitor. Is there a way to test that (safely) with a multimeter?

It seems like replacement should be pretty darn easy, but any tips on doing it safely?

Is this the sort of thing that you can pick up at HD or Lowes?

It's going to be a long night. I guess I'm really glad that it seems like it didn't quit until somewhere between 8:00 and 8:10 instead of earlier in the day. But then if it had died earlier, I may have had time to get home, get it diagnosed and get home before HD and Lowes closed. I wonder if any neighbors have a capacitor they aren't using?

[masraum]

Hmm

if the fan is not running is the compressor not running also...if neither is running the possible reasons are 1..no power to outside unit...2..bad contactor on outside unit.is this buzzing if it is this indicates no power...3 bad capacitor,do both compressor and fan humm then quit humming and hum some more...

1 Well, I have 240 outside.
2 hmm, I had buzzing, but no activity
3 I think I had more of a buzzing than a humming, so maybe it's not the capacitor.

So what the hell's the contactor and how do I check it?

[masraum]

OK, so the contactor is basically a big relay that supplies the 240V to the outdoor unit. I assume if I see 240V on both sides of that thing that it's not the contactor?

[kaisen]

We had the same issue last year. It was a bad capacitor

[slakjaw]

Sounds like a capacitor to me.

[porsche4life]

I'd call a 24hr ac guy. Life's too short to sleep a night or two in the heat while you figure it out.

[masraum]

Originally Posted by kaisen

We had the same issue last year. It was a bad capacitor

Originally Posted by slakjaw

Sounds like a capacitor to me.

Yep, found a test procedure on the net. Definitely looks like a bad capacitor. Now I just need to find the closest place that opens early to get one.

Originally Posted by porsche4life

I'd call a 24hr ac guy. Life's too short to sleep a night or two in the heat while you figure it out.

Well, yeah, that's probably true. I'll call and see what a service call would run. I'd hate to pay a few hundred dollars for a $10 part, but I'd also hate to be hot all night if I could tell someone what I need and they can come out and have me up and running quickly for not too much money.

[masraum]

I checked with the missus. I asked her if she would rather pay $25 in the morning or $200-300 tonight. She's willing to sleep a little warmer than usual, so I'll run down and grab a new capacitor in the morning.

[futuresoptions]

Originally Posted by masraum

I checked with the missus. I asked her if she would rather pay $25 in the morning or $200-300 tonight. She's willing to sleep a little warmer than usual, so I'll run down and grab a new capacitor in the morning.

PM Sent

[masraum]

Thanks tons for the assistance, Bill. It was worth a shot. I'll grab some parts in the morning. Hopefully, I won't pay more than $40 or so and I'll be back up and running with new parts.

I guess this is the time when it would be nice to have California weather.

[cabmandone]

The humming or buzzing is most likely your contactor where your main power attaches at the unit. As for the compressor and fan not running, it could be the cooling contactor inside the unit or the capacitor. If the capacitor is one of the round or oval metal type, look for any deformity in the housing. Normally they will have some sort of bulge in them when they go bad. BE CAREFUL when you install the new capacitor. I saw a condensing unit with a short cause one to explode once. When you install the new capacitor, make sure you have the power off and the thermostat turned to off. Once installed, turn the power on and then have someone turn the thermostat to cool and if necessary turn it down to create a call for cooling. Stand back from the unit and watch to see what happens. If it starts running, great, problem solved. BTW, most outdoor units have a time delay built in as do most modern thermostats so if the outdoor unit doesn't kick in right away don't be alarmed it could take 30 to 90 seconds before it does.

Something you checked was power. Did you physically close the contacts on the contactor? That buzzing could mean the contacts didn't fully close and you weren't getting power to the fan and compressor. Take an insulated screwdriver and in the center of the contactor you should see a small bar with a spring, press that bar in and it will close the contacts. Let it go and it will open them. Since the indoor fan was running that tells me the thermostat is calling for cooling but it's possible your cooling contactor in the outdoor unit did not close. Visually inspect the capacitor and try closing the contacts manually with a good insulated screwdriver before you go get parts. Please be careful! You're welcome to drop me an email through pelican if you have any more questions. I'll be on the road today but will be checking messages.

[Baz]

FWIW I've had my share of AC outages and decided a while back to install a small window unit in my living room just for emergencies. It's a small 110v unit and fits in one of the many windows I have on the north side. Very handy, very affordable, easy to install, but priceless when it is needed.

Good luck with your repair - I replaced a bad capacitor once but it was for my air handler and effected fan speed.

[red-beard]

Johnstone supply. They are everywhere. Get the model of the part and/or the AC unit.

[red-beard]

And if you were closer, I'd loan you a portable unit, I have 4 for cooling my assembly area at my business.

[red-beard]

Remember - Walmart has window units for $109...

[billybek]

Could be the capacitor.
The start capacitor typically is round and the run capacitor is oval in shape although there are some out there that have both in the same housing.
There could also be a start relay that brings the start capacitor in at startup and cuts it out when the unit is running.
As mentioned before, make sure the contactor is closing all the way. No critters inside.
If you have a multi meter, disconnect power from the unit and remove the terminals from the compressor motor terminal board.
Check ohm values between Start, Run and Common terminals.
Check for a breakdown in resistance between any of those bare terminals and Ground (copper pipe or bare metal on compressor)
Check the condition of all the wiring connections (burnt/hot looking).

[onewhippedpuppy]

I would try cabmando's advice before buying parts. Make sure the contactor is closing, which can be confirmed with an insulated screwdriver. BE CAREFUL. You have full voltage at the contactor, I've seen a screwdriver slip and arc across contacts and knock a man on his ass. I used to do a variety of maintenance and repair work years ago, by far the most common A/C issues were the contactor and starting capacitor.

[javadog]

If it's a capacitor, try not to buy one made in China, so you aren't changing it again this weekend.

JR

[stomachmonkey]

Originally Posted by javadog

If it's a capacitor, try no to buy one made in China, so you aren't changing it again this weekend.

JR

Sounds like a capacitor, could be cooked relay contacts as well.

Do not cheap out on the cap, buy US made only. May cost you $75-80 but cheaper in the long run.

[masraum]

Originally Posted by cabmando

The humming or buzzing is most likely your contactor where your main power attaches at the unit. As for the compressor and fan not running, it could be the cooling contactor inside the unit or the capacitor. If the capacitor is one of the round or oval metal type, look for any deformity in the housing. Normally they will have some sort of bulge in them when they go bad. BE CAREFUL when you install the new capacitor.

Something you checked was power. Did you physically close the contacts on the contactor? That buzzing could mean the contacts didn't fully close and you weren't getting power to the fan and compressor. Take an insulated screwdriver and in the center of the contactor you should see a small bar with a spring, press that bar in and it will close the contacts.

Thanks, yes, Bill (futuresoptions) thought the same about the contactor (why don't they just call it a relay?). I sent him some pics and the contacts looked like an old set of points (but bigger). He had me try sanding those a bit to see if that would help. Last night while I was troubleshooting, I checked the voltage on both sides of the contactor and with the AC in the "on" position, I did have 240V on both sets of terminals. I also tried what you mentioned by pushing the bar in and it seemed to make no difference

I didn't see a bulge in the capacitor, it was one of the cylindrical models with the fan and compressor capacitor built into one unit. Last night I put a multimeter on it and did not get 35uf and 5uf on herm and fan which I thought was a pretty good indication of failure. This morning when I pulled the capacitor, I noticed that the top was bulging some, but since the top was supposed to be domed anyway, it wasn't very obvious in the dark when I looked last night.

Originally Posted by red-beard

Johnson supply. They are everywhere. Get the model of the part and/or the AC unit.

Yep, that's where I ended up. I'm glad that they sell to the public, the first place I tried did not.

Originally Posted by red-beard

And if you were closer, I'd loan you a portable unit, I have 4 for cooling my assembly area at my business.

Thanks, Red! Yeah, I didn't even think about a window unit last night, and we've got a 24hr Walmart less than a mile away. It's funny, last night our low was 77 (stayed 80-82 in the house). But the night before last it got down to 67. Why didn't the damn thing break Tuesday instead!

Originally Posted by billybek

Could be the capacitor.
The start capacitor typically is round and the run capacitor is oval in shape although there are some out there that have both in the same housing.
< some text snipped >
Check the condition of all the wiring connections (burnt/hot looking).

Thanks all for all of the help and advice. I found a local place that sold to the public this morning and replaced the capacitor ($34), and we are back up and running. I was going to replace the contactor anyway, but we aren't planning to be in the house much longer and it's still working so I decided to skip it for now. It's still a little warm in the house, but the temp is coming down. It feels much better than it did earlier this morning.