It's hot outside.

Inside the temp is approaching 90 degrees. I need some help troubleshooting the AC.

The thermostat seems to be working. And it triggers the fan to come on. The problem is the unit outside (condenser?) isn't coming on. I can hear some electrical humming but the pump or blower fan aren't on (I need to double check the blower fan but definitely the loud condenser isn't on).

I replaced the caps at the condenser and upstairs (at the furnace / blower / evaporator) about 5-7 years ago. The one outside seems okay - at least nothing visually wrong. Haven't checked upstairs yet.

I'm thinking something at the condenser unit is broken? But there doesn't seem to be much there except the cap and some sort of copper coil (small transformer?).

I'd appreciate some help trying to figure out what might be wrong and how to test. Then perhaps to find a replacement part.

If the (loud) fan on the outside unit is not coming on, and it's humming, I would be thinking capacitor. Don't let sit and and try to start for too long.

Start/run capacitor is my bet. Last one that I had fail didn’t swell up or show any outward signs of failure.

Thanks guys. Is this a premature failure or is 5-7 years a reasonable lifespan? Just wondering if I should buy 2 (and replace the one in the attic as well) or just replace the one.

Is there a way to test this without killing myself? I have a Fluke.

My AC had the same symptoms. It was the start/run cap. In my case, it is a 5/45 ufd Capacitor, costs around $25

Almost certainly the capacitor.

Be careful, though. A short discharge through one can be dangerous.

quote:

Originally posted by konata88:
Thanks guys. Is this a premature failure or is 5-7 years a reasonable lifespan?

~5 years is the average lifespan, and often less. Based on that age and the symptoms (thermostat and fan work, but compressor and/or blower won't kick on), it's most likely going to be that start/run capacitor on your outside unit.

quote:

Is there a way to test this without killing myself? I have a Fluke.

Yes, if you have a multimeter. It's pretty simple. There are step by step Youtube tutorials for testing a HVAC capacitor, such as: https://www.youtube.com/watch?v=m2wHS4uJUfU

But even if you don't want to mess with testing it or don't have access to a multimeter, just tossing a new $20 capacitor on the outside unit would be a reasonable first troubleshooting step in this case.

quote:

just tossing a new $20 capacitor on the outside unit would be a reasonable first troubleshooting step based in this case.

Provided you understand the risks and procedure for discharging the old capacitor. Watching the videos on utoob are good, you'll learn what to do, and watch plenty to get it down.

Yeah, the video I posted above goes through how to safely discharge the capacitor, before it ever gets into how to test it.

And the OP stated that he's already replaced the capacitors before. So hopefully he knew how to safely do that already...

Clogged condensate line followed by bad run caps are by far the most common reasons our ACs stop running.

Thanks guys.

I've replaced it once in all my years - I was gonna ask again how to safely discharge. I'll watch the video.

I think I found a cap locally in stock. Will test and then go buy one. If test indicates the cap is still working, I'll come back here first.

Usually a clogged condensate line cuts power to the thermostat, which then reads a power error. It's worth a look, but I still think that since the compressor is making noises like it is trying to start, it is getting signal from the thermostat, and the problem is in the capacitors.

Both are possible, though. Our AC failed last week for a clogged condensate line, and it just took a quick shop vac effort to clear it.

quote:

I was gonna ask again how to safely discharge.

Use a screwdriver to short the terminals on the cap.

quote:

Originally posted by ArtieS:
Usually a clogged condensate line cuts power to the thermostat

Yeah, if my line clogs and the drain water backs up, the float switch kills power to the thermostat and the thermostat's LCD display goes blank.

My daughters AC went down last week. Symptoms similar. I replaced capacitor, no luck. The problem was a bad condenser fan, I bought an aftermarket one so far so good.
Oem fan>>>585.00
Aftermarket >>>285.00

Test your fan.

Thanks guys!! I appreciate the quick and specific help.

Looks like it was the cap at the condenser. I replaced it and cool air is being delivered!!

And I didn't kill myself - was still very apprehensive and tried to short the cap 5 times with a very long screwdriver.

The cap measured 1nF on the Fluke. Both Herm and Fan.

Dumb question: If they didn't have my size in stock (35+5), can I use a different size, at least temporarily? Or is that very bad? Not sure which way would be okay - 40+5? 30+5? How much different would be okay if the one I need is not in stock?

I got lucky this time and bought the last one.

Is it too late to suggest calling the man ?

Capacitor is the easiest to trouble shoot and a common failure.

quote:

Dumb question: If they didn't have my size in stock (35+5), can I use a different size, at least temporarily?

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I believe you can only deviate 10%.
The first number is for your compressor, you don't want to ruin that.

Call your local hvac supply house, they will have it or get the right one.
But if the supply house is like the ones here they won't sell it to you. But ask who will sell to you.

I had to have a plumbing company get my parts then I buy from them.

Last year I bought a spare from Amazon, but it was a bait and switch.
I received a generic chicom cap. and it was a smaller diameter than original one so wouldn't fit in the bracket.
Sent it back.

I don't know why most hvac wholesale supplier only sell to repair shops.

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Glad you got yours fixed.

Just a FYI: Around here there has been a rash of the outside unit not coming on and the Start Capacitor is actually fine, not needing replacement.

This is just a FYI but it's interesting and something one can ask the AC repair guy about.

It's just a weird year, it happens, but honest repairmen have found the contacts in the outside unit packed with spiders and ants and little tiny insects that prevent the contacts from closing all the way properly.

A little bit of cleaning out the infestation and the contacts and all is good for most people.

In some cases an honest AC repair guy has had to actually replace the contacts, but that is very cheap and easy to do.

BEWARE BEWARE BEWARE, don't even thinking about looking inside the unit until THE POWER IS PULLED AND OFF !!!!! This is high voltage!

Electricity and a limp schlong, what do they have in common? One does NOT f*** with either.
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