When running , my heat pump seems to have a sympathetic vibration down around 2 or 3 Hz. In other words, besides the normal sounds of the fans and compressor, I hear a low rumble that gets louder and softer a few times a second. It sounds like a beat frequency–a frequency heard when two items are vibrating at very slightly different frequencies–if you’re musically inclined.
I thought it was something vibrating and tried checking for loose mounting hardware, made sure there was nothing loose in the cabinet, etc. I noticed that one of the copper tubes going to the cooling fins could vibrate against another one and gently moved it out of the way. That helped for about a day and now the noise is back, maybe a little louder.
It doesn’t make the noise when just the fan is running. It starts when the compressor kicks in. On the compressor side of the cabinet is a fan to move air over the coils and it doesn’t seem to be that one. Are there moving parts in the large black canister that I am assuming is the compressor itself? (Has copper lines going to the fins.)
Unfortunately, the AC is on the roof above my bedroom. This noise travels nicely through all the framing and makes sleep a little harder than normal to achieve.
I’m about ready to pay through the proverbial nose for a service call, being in Phoenix, but if there’s anything I haven’t checked out (that I can) I want to do that first.
I don’t know your capabilities, but it is common for the rubber shock-mounts under the compressor to deteriorate over time (and with heat), which can couple the compressor noise through the body of the unit. You might want to take a look at them.
The compressor (in the outside unit) is typically mounted with 3 or 4 bolts going through the compressor feet, then through some hunks of rubber (like large grommets), and then through the frame. Just one thought.
Actually, Khendrask, that’s exactly the direction my own troubleshooting was taking me. The noise is almost certainly from the compressor. The mounting points seem like a good avenue to transmit vibration.
After seeing your note yesterday, I pried one of the rubber feet out from under the compressor and took it to a local parts supplier who told me that it was in better shape than any he had! (My A/C was made by Goettl and they’ve been out of business for a while.)
I’ve loosened the bolts that go through the feet. (The counter person at the parts store suggested discarding them entirely, but I’m not sure that’s the best idea.) IF this doesn’t work, I may have to have a service call that I am almost certain will result in a recommendation to replace something expensive.
Ask the service tech to check for correct “superheat” and “subcooling.” (especially superheat)
There is no way to troubleshoot this over the internet, especially with the scant info we have to work with. However…your compressor is basically a vapor pump.
My swag is that the compressor is seeing some liquid refrigerant at start up. I would make sure that the refrigerant charge is correct. (and many techs consider ‘close enough’ to be ‘good enough’)
The other thing I might look at is your ‘crank case heater.’ Your CCH slightly heats up the compressor to keep liquid refrigerant from migrating to the compressor.
Check those 2 things and maybe your problem goes away.