Air Conditioner's Compressor Start Capacitor Blown

[kdarling]

I know that others here have recently had similar problems, so just wanted to document it.

It's been so hot and muggy lately that I've been running the air conditioner while the Chinook is in the driveway.

Went out to check on it yesterday and whereas the fan was running okay, the compressor was trying to start but failing, making a humming sound while pulling a huge 15 amps for a few seconds according to my new built-in AC meter, then giving up and trying again a bit later.

I went online and read the service manual and saw that it's probably the start capacitor. (You're supposed to set an analog meter to its 500 VAC scale, and use the probes on the connections to discharge the cap. Then disconnect it and use meter set to highest ohms scale to check each pair of cap terminals between C for common and any other pins. Meter should show continuity at first and the slowly move towards infinity.)

So I climbed up on the roof today with a meter to test it, opened the top of the AC and the metal shroud surrounding the capacitors and pulled out this mess:

Start capacitor insides

Top of the cap was off, with paper and foil guts everywhere. I think it qualifies as a blown start capacitor

I ordered a new one off Amazon for about $7. Should have it in Monday and I'm hoping that's all I'll need.

[Blue~Go]

Well that's conclusive. Jeepers.

[Rokrover]

No need to troubleshoot or safely discharge this one with a voltmeter; looks like a stick grenade went off. Seems the relay attached to the red wire is still serviceable?

Some internet gurus recommend replacing the run capacitor at the same time. I believe it is the larger one in your picture. They also talk about benefits from a “hard start” capacitor designed for the increased torque with newer freons. Probably best to stick with the original specs.

Have fun up there on the roof and let us know how it went

P.S. I used to live in northern New Jersey and know how muggy it can get there.

[kdarling]

One thing I did find out NOT. to do:

There was a paper circuit diagram of the capacitors section on the metal shield.

As usual, I decided to take a photo of it and upload to my private Pinterest board so it would be available to me for later reference.

But, stupid me saw some dirt on the diagram. So without thinking, I dipped my fingers in a roof puddle of rain water from the night before, and used it to try to wipe the dirt off the paper.

Uh, nope. Water + paper = shredded paper where I wiped. Idiot.

Fortunately I was still able to see most of the diagram, but man I wish I had not sprung into cleaning action so fast.

Grrr. Presented as yet another cautionary tale in the hope that my mistakes will save someone else

Update: good copy of the circuit diagram:

9954F710-1977-4BC4-8F3D-B46CE8376B54.png (8.89 KiB) Viewed 3121 times

[kdarling]

Well, installed the new cap, went inside and turned on the AC and... nothing for about ten seconds, and then a loud pop from the roof. No, it didn't explode this time, but it clearly isn't working either.

So it looks like it's time to investigate either another roof replacement or maybe pursue an idea of adding a split system with the main unit mounted at left rear above the spare tire / locker area.

More bad news: both of my solar panels now read full voltage but only 0.2 Amp output. From what I've read, that means an internal failure.

We did have some big storms the other day.

Sigh. Just when I thought everything was up to snuff. So it goes!

[Blue~Go]

I guess Rokrover successfully sent Murphy east

More bad news: both of my solar panels now read full voltage but only 0.2 Amp output. From what I've read, that means an internal failure.

I have two 100 watt panels that I (happen to have) in series (not that it matters for this). When they were about 6 months old -- so, long enough for me to know their habits, but still pretty new -- I suddenly noticed things weren't charging quite like they should. They were charging, but... slooooowly. The voltage was up at the expected number (around 35 in my case), but the amperage coming out of the controller was only half the usual (5-6 amps instead of 10-11). Hmmm...

My batteries should have been bulk charging (since by the time I was figuring this out they were down to around 79%), so I knew it wasn't because they were too full to take anything. So what gives?

I then hooked up each panel alone and sure enough, one was putting out full power and the other... nothing. Voltage yes, but no oomph (amps). It was then that I noticed that panel's junction box was totally deformed. And smelled like melted plastic. Well that's not right. (And I'd been in a cool place, with plenty of air under them.) So the diode box had melted. Since they were less than a year old, the company sent me a new one. Figured I'd tell the story in case it had any useful info in it.

[Rokrover]

As B~G surmised, perhaps Murphy already dispatched his battalions to the eastern front?

Perhaps the relay was bad? My armchair reference says:

The relay has to take the start cap out of the circuit in less than a second or the start cap will blow. The run cap is made to stay in the circuit.

[kdarling]

Thank y'all for the encouraging responses... they actually helped.

First, turns out that under the shade we have up here, 0.2 amps is normal for a working 50w solar panel. Once I found some real sunshine, I was able to determine that the rigid Renogy panel was working, but the flexible one on top of the AC shroud apparently is not. Ah well, half is better than none!

--
As for the AC, after first searching for a low profile replacement model (I don't want to be higher than my current 10" Penguin), I started reading up on why start caps blow.

One reason a compressor can lock is if power is lost while running, due to temporarily too much pressure differential for it to start again. Remember thst I mentioned that storms had come through, and I'm sure the power glitched a few times. So I waited a few days for the pressure on each side to equalize, installed a $33 Dometic Hard Start cap kit, and yep... she fired up just fine and has been running all day. Yay!

Dometic Hard Start Kit

Downside is that such a lockup probably does reduce overall lifetime, and my newly built-in AC power meter says it pulls more amps than it did before. But I'm okay with not spending $500-800 for a full replacement unit right yet