Window air conditioner suddenly randomly tripping circuit breaker
July 9, 2014 8:36 AM   Subscribe

We have a window A/C unit that is about three years old. Since we bought it, it has worked flawlessly to cool our bedroom for the few weeks a year that we need it... until now. We put it back in the window last Wednesday, and it worked fine until Monday evening. Now, seemingly without rhyme or reason, but usually (of course) in the middle of the night, it will trip the circuit breaker.

Tripping the breaker is particularly annoying because both my wife and I have sleep apnea and our CPAPs are on that circuit. So we wake to sudden silence unable to breathe.

It first tripped Monday night about 1 AM. I went and reset the breaker and it tripped again two hours later. At that point I reset the breaker again, turned off the A/C, and opened the windows. I started it up again yesterday morning and within thirty minutes, it had tripped the breaker, so I reset the breaker once again and turned it off.

I checked and cleaned the unit's air filter yesterday afternoon, and the A/C ran fine for the rest of the afternoon and well into the night, but again tripped the breaker at about 1:30 AM.

It seems odd to me that the A/C unit would trip the breaker in the coolest part of the night. Indeed, last night, the outdoor air temperature was in the low 60s, cooler than the inside of the house. The compressor shouldn't even be running at that point, I wouldn't think.

Is there an A/C failure mode that would explain this? If it seems obviously an A/C issue I will buy a new one immediately. Alternatively, is it more likely that it's a problem with the circuit breaker? Our house is only about 4 years old so I wouldn't think it would be that.
posted by kindall to Home & Garden (14 answers total) 1 user marked this as a favorite
You've got too much on the circuit. Can you get a mega extension cord and plug the CPAPs on one circuit and the A/C on the other?
posted by Ruthless Bunny at 8:40 AM on July 9, 2014 [6 favorites]

Are the CPAP units new to the house and your evening sleep (since last summer, I mean)?

Adding them to the mix may have put that breaker over the edge.

Can you run a properly rated heavy duty extension cord from the window AC to an outlet on a different breaker?
posted by Buttons Bellbottom at 8:40 AM on July 9, 2014 [2 favorites]

Moving the CPAPs to a different circuit will help, if the addition of them is recent. If this isn't an option, maybe consider attaching the CPAPs to an uninterruptible power supply. It will give an audible alarm when the breaker trips, but the machines should keep functioning for a bit.
posted by soulbarn at 9:04 AM on July 9, 2014

Make sure that the filter and coils (if accessible) are really, really clean. My window AC was doing this same thing and stopped immediately once I mucked out the rather gross amount of dust and cat hair that was clogging it up and probably causing it to work a lot harder.
posted by Rallon at 9:10 AM on July 9, 2014

We've had the CPAPs for a couple years and didn't have this issue last summer. And the breaker has tripped when the CPAPs aren't in use.

Something has obviously changed, I'm just wondering if it's the A/C unit or the circuit breaker to blame.
posted by kindall at 9:11 AM on July 9, 2014

Breakers can get weak and go bad also. They are pretty easy to change and usually inexpensive. I would give that a try (or hire an electrician to give it a try if you are not mechanically inclined). Also the wall outlet can go bad and is also easy and cheap to replace. IF you have GFCI outlet on the circuit (even if it isn't used much) can also make the breaker trip.
posted by bartonlong at 9:18 AM on July 9, 2014 [2 favorites]

Have a look at the A/C's power cord -- if it's damaged, that could be tripping the circuit.
posted by Iris Gambol at 9:36 AM on July 9, 2014

I'm voting on the weak breaker thing. If you need to run relatively medium-high current stuff like TWO CPAPs, spend the couple hundred bucks to have an electrician and get a single outlet circuit installed for it. Assuming this isn't a rental, obviously.

A thing to try first though, is haul it into another room and plug it into an outlet on another circuit that nothing else is really on. Does it blow that too? then it's probably something funky in the AC. If not, that circuit was just chronically overloaded and the breaker has gotten weaker.

The cleaning advice is good too, but would only really apply once it's been on for a while and has heated up the hot side i'm thinking. Clogging would cause less load on the fan because it has less air to push against.

Every time i've had this problem, with the exception of one unit that was actually just boned and wouldn't run for more than two seconds it was just a tired overloaded breaker.
posted by emptythought at 10:08 AM on July 9, 2014 [2 favorites]

A standard circuit (in the USA) provides 15-20 amps. What is the current rating on your CPAP machines and on the A/C? This information is printed on most electrical devices, often on a sticker or plate near the plug/power cord interface.

If you've already verified there is no way you are even getting near 15 amps with the current ratings on those three devices added together, definitely try the suggestion above of plugging the A/C into a different circuit and seeing if that one trips too.

Another question: what else is on the circuit being used by the A/C and CPAPs? A while back, we had a problem in the lab where I work with a circuit that seemed to trip at random when nobody was even around, etc. Turned out in that case that we had two refrigerators (plus a couple of small items) on the same breaker, and what was happening was that we would momentarily go over current due to the fridge compressors cycling on and off. So unless you know for sure something else isn't using the same breaker, you could have something like that going on.
posted by aecorwin at 1:39 PM on July 9, 2014

My CPAP has a humidifier built into it. I don't know this for sure, because I've never tested it, but I would bet that the humidifier has to run "hotter" as the night gets cooler. Maybe when your room cools off in the dark of night your CPAP units are using more electricity than they were earlier in the evening and this is causing the breaker to flip.
posted by tacodave at 2:52 PM on July 9, 2014

Another data point as I was just checking the breakers in case I need to replace it...this is an arc fault circuit interruptor. It's my understanding that these can have false positives on appliances. Any chance off that being a factor?
posted by kindall at 3:20 PM on July 9, 2014

CPAPs pull jack for power and should co-exist with your A/C no problem.

While you could have some electrical gremlin there is a good chance this is being caused by a dirty condenser coil causing high head pressures, excessive current draw by the compressor and eventually tripping the breaker. Because it is the cheapest thing to test I'd address this first.

The best way to clean the condenser is with a pressure washer. If you don't have one we used to use commercial U-Do car washes. If you can't transport the unit you can also get acceptable results with a garden hose. Once you have the unit at the place you are going to wash it spray the heck out of the coils with Simple Green. Then rinse out the coils until the water runs clear. Be careful with the pressure wand; the fins are easy to bend over. Keep the pressure nozzle at least 18 inches from the coils.

Also try to avoid spraying water in the controls.
posted by Mitheral at 4:32 PM on July 9, 2014

Yeah, I looked at the power draw on the CPAPs and they are a max of 60 watts each. Probably not the deciding factor.

It kicked off again last night at about 1:30 AM. That seems remarkably consistent time-wise, but I don't know of any other power draw on that circuit that would be active at exactly that time.

I'm going to move it to another room and run it on a different circuit all day today and see if I can cause that breaker to trip.
posted by kindall at 6:25 AM on July 10, 2014

It ran fine all night... so I guess we're voting for the breaker. I'll replace it this weekend and see if it resolves the issue.
posted by kindall at 9:08 AM on July 11, 2014

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