Home HVAC question - ID a noise

[luvtheheat]

I have an American Standard 5 ton split AC/gas heater with an outdoor freon compressor unit (Model 4A7Z0060A) to cool my 1750 sq foot house. Installed in 2009. It's a two speed unit that for 80% of summmertime use stays on low compressor/fan speed. It runs on high speed as needs, so no problem with capacitors as far as I can tell.

When the compressor is running on low, every so often I'll hear a very distinct single click noise. The unit stays running on low. Other than the noise, it seems nothing is wrong. The house is cool all the time in summer.

The click sounds kind of like a hammer hitting the frame of a car, some sort of metal to metal contacting.

Anyone have an idea what that noise is? If I had to guess, and so far I do have to guess, I'd say it was a capacitor discharging occasionally.

Is that normal?

Thanks in advance

 

[BillK]

A capacitor discharging would not make a "banging" noise. Any chance the fan is hitting something every once in a while ? Does it do it often enough that you could record it ? Very hard to try to figure out a noise without actually hearing it.

 

[4x4Pete]

Is there any chance that a drop of water from a condensate drain is hitting the fan? It would make a loud noise. I think you would have diagnosed this though.

 

[karoc]

If you can time it correctly maybe watch you compressor to see if it jerks. Wonder if it’s at that threshold between low/high. I have no experience with these two speed compressors

 

[luvtheheat]

Update: Took panel off compressor unit and found RUN LOW capacitor was bulging at the end. Just bought all 3 caps on Amazon. $85 or so. RUN LOW, RUN HIGH, START. Figured may as well replace all 3 on this 13 YO unit.

 

[bubinga]

Update: Took panel off compressor unit and found RUN LOW capacitor was bulging at the end. Just bought all 3 caps on Amazon. $85 or so. RUN LOW, RUN HIGH, START. Figured may as well replace all 3 on this 13 YO unit.

Let us know it that was the noise.

 

[luvtheheat]

Let us know it that was the noise.

I'm thinking that the noise is from the "contactors", but after having read up on what the heck those are, I won't blame/replace bad contactors until I have all new caps.

 

[bonneyman]

Noise complaints were some of my hardest troubleshooting jobs. Many times I couldn't hear anything unusual, but the customer was saying it was driving them crazy. Intermittent noises were the worst!

Alot of times with heat pump calls I'd get customers telling me about all sorts of "weird" sights and sounds. Over many years of contracting I finally figured out most of those kind of calls were due to a defrost malfunction of some kind. And customers not educated on how oddly heat pumps operate.
"Smoke" coming out of the unit. Condenser burning something? No, that's steam from the defrost cycle. Heats fine, then "cold" air for like 10 minutes every hour and a half or so, like clockwork. Yep, that's the frequency and length of the defrost cycle. Banging, groaning, vibrating, humming, buzzing, shaking noises like the system's going to take off like an F-16? Nope, defrost cycle switching pressures and running high head because of a cycle termination problem, or tubes running too close together, or the unit not securely attached to the base. Maybe vibration being transmitted to the adjoining wall.

 

[snyder]

Do any of your fan motors have the centrifugal switch plate?
They will make a click upon start and stop.

 

[luvtheheat]

Update: All 3 caps were leaking or bulging. Replaced RUN LOW, RUN HIGH, START.

After replacing, I left the cover off and supplied power to the unit and watched/listened. After the usual 3 minute wait after full power shut off, the unit started up. The click noise I mentioned in my first post was the "contactor". My unit has two contactors, one for the low pressure compressor, one for the high pressure compressor.

What I was originally hearing was the unit switching from low to high compressor, and the high contactor engaging. What I "thought" should happen was that when it switched from low to high compressor, that the fan speed would also increase. Apparently it does not at that moment. Fan speed does increase a few minutes later if needed.

So far as I'm concerned, the noise is normal.

If you've got a 10+ year old unit that gets a lot of use, I'd look hard at proactively replacing all the caps. I paid about $75 for all three. Took me less than an hour to replace them; had to rework one strap due to the size of that cap had decreased.

I also saved probably $300 for a service call and at least another $50-75 per cap if done by an AC Tech.

That will buy a nice dinner out

 

[luvtheheat]

Do any of your fan motors have the centrifugal switch plate?
They will make a click upon start and stop.

I don't know. How would I tell? I looked at the schematic and it didn't reference it.