Home AC makes loud buzzing sound

[themechanic]

I just noticed a loud electric buzzing sound when my home AC comes on. It seems to be coming from my outside unit when the fan is running. Is the fan going out?

 

[gkent]

My guess is the compressor is shot. Does it actually "cool" or not? The fan may run but that doesn't mean the compressor is working.

 

[dadsbee]

Buzzing.. like a relay chattering?

 

[themechanic]

The fan runs and the system cools well without a long run time (run time is average). I'll get a recording and post it.

 

[toolmanmike]

The fan runs and the system cools well without a long run time (run time is average). I'll get a recording and post it.

Get out your nutdrivers and take the sheet metal cover off. You should be able to figure out what it is that's making noise. It might be a loose cover or a couple missing sheet metal screws.

 

[themechanic]

 

[toolmanmike]

Yep that's loud. I would shut it off and cal the HVAC repairman if you don't want to mess with it yourself.

 

[themechanic]

The compressor was installed in the late 90s. Since then, the contactor was replaced and the fan was replaced a few years ago.

 

[themechanic]

Buzzing.. like a relay chattering?

I wouldn't know.

 

[dadsbee]

That's a relay eating itself.. or maybe the motor capacitor taking a ****.. shut it off..

 

[themechanic]

It cycles on and runs 7 minutes.

 

[toolmanmike]

It cycles on and runs 7 minutes.

Shut it off and have a pro check it out. Sounds like it is short cycling to me. It doesn't run long enough to remove much humidity. It will cool but it will be clammy. If your humidity inside your house isn't 50% or lower it isn't running long enough. Many contractors install too big of unit and that's what it does.

 

[metaldad]

contactor needs replacing (again, for you)
$25 at a supply house

 

[dadsbee]

Yep.. why I put a 1.5 ton in a 6000 square foot house!

 

[themechanic]

It's 93 F with humidity at 47% outside. The thermostat is set at 78 F.

 

[metaldad]

93 inside!!!!!!!!!!!!!!!
go get a hotel room for the night

 

[themechanic]

I noticed a lot of spider web around the area where the contactor is with dead bugs caught in it. There's also some ant activity in the area.

 

[kiwigtx]

Sounds like either;
1. Contactor has a light film of corrosion on the magnet faces - causing chattering,
2. Motor is delaminating in the stator,
3. or, there is a mechanical rubbing of the fan blade itself.

A dirty contactor face will not allow it to clamp shut instantly when energised, and can sit for hours chattering/buzzing like that. Replacement is best.

 

[dadsbee]

Ants LOVE the humm of electricity...

 

[themechanic]

Ants LOVE the humm of electricity...

That's what I heard/read.

I found my receipt from Comfortgurus for the contactor I replaced in AUG 2014. Looks like it's time to replace them again.

 

[dadsbee]

Turn it off, pop the covers, check out the contactor.. .. clean it, give it a hit, what ever it takes.. turn it back on. See if you can keep her running, otherwise you're asking for bigger issues.