I upgraded from a 30 year old Trane central AC to a Lennox in 2018 and it's been great except for one issue; each time the AC kicks on, I hear a noticeable "BZZZZZZZT" noise and I've mentioned this to the HVAC guy who installed the system and asked him to check this for me when he came to service/check the furnace for the season. He stated that he tightened all the connections from the breaker panel to the condenser and asked me to check and listen in the spring or if it goes above 60 degrees again (right now it's 40's - 50's).

The cable run is a pretty long one which I'm starting to wonder may be the issue, from the breaker panel to the condenser, I measured and it's about 75 feet give or take. The cable is 10/2 Romex and runs from the panel (on a 30 amp breaker) through metal conduit for about 25 feet, then goes to a junction box and then is just Romex through the joists until it goes out the wall to the disconnect and whip. I'm assuming this was installed in 1988 or so when the original Trane unit was installed? I never noticed any sort of buzz or other sound when the old system would kick on, we had replaced it due to age and also because we converted from oil to natural gas.

I'm looking at some websites that let you calculate voltage drop and it's saying for that long a run, I really should be using 8/2 wire, NOT 10/2. Could this be the source of that buzz? Maybe the Lennox has more of a draw when starting up than the Trane did?

I'm planning on upgrading my dinky 100 amp service to 200 amp next year anyway and was thinking that maybe I should have that cable replaced too.

Any thoughts here? I really hope I'm not putting any sort of strain on the AC each time it kicks on that will cause it to fail before its' normal end of life?

go look at the amp draw on the unit.

http://wiresizecalculator.net/...tors/voltagedrop.htm

at 25 amps it drops 4.66 volts 1.94 percent not sure what's causing the buzz capacitor maybe on start up.

Would need the electrical requirements of the unit to know what needs to be run to it.
It will all be listed on the label stuck to the outside of the condenser.

MCA, Minimum Circuit Amps
MOCP, Maximum Over Current Protection or Max CKT BKR, Maximum Circuit Breaker

* I'd be very surprised, if the new unit required a larger feed.
10/2 on a 30 amp breaker is pretty common and adequite for most units.

I'd be leaning towards a noisy contactor.

My Lennox makes a similar noise. My run is under 20ft.

My old unit did similar.

Not always noticeable but there is a definite starting noise.

Could be the contactor . They usually operate on 24 volts and that's a long run for that low of a voltage . Smaller wire too .

quote:

Originally posted by selogic:
Could be the contactor . They usually operate on 24 volts and that's a long run for that low of a voltage . Smaller wire too .

I do not see any wiring like that running out there, just the main power cable which I realize now is most likely 10/3 and not 10/2, right? 240V? Two hots and a neutral?

It’s more just an annoyance to me.

Since you are planning on replacing the panel and maybe this run of wire next year, maybe do the A/C wire now to take that question out of puzzle?

I know that isn't the answer to your original question but I'm not an electrician, and much better versed in 12V, so here's another one. Maybe there is some sort of clamp type meter that can check the voltage or at least amperage out near the unit when it kicks on and makes the noise. As an alternative, a volt meter on the terminals themselves to check the actual voltage drop under the load.

Go down the U Tube rabbit hole and look for "air conditioner relay contactor buzzing".
Over the years I've had a few of them get pretty loud.

quote:

Originally posted by PASig:

quote:

Originally posted by selogic:
Could be the contactor . They usually operate on 24 volts and that's a long run for that low of a voltage . Smaller wire too .

I do not see any wiring like that running out there, just the main power cable which I realize now is most likely 10/3 and not 10/2, right? 240V? Two hots and a neutral?

Wrong, 10/2 with ground. Two hots and a ground.
There is 18/2 for the control wiring... 24 volts to operate the contactor.

Still see no issue with the wiring.

As posted above, need the info off the unit to know for sure...

quote:

Originally posted by PASig:
The cable run is a pretty long one which I'm starting to wonder may be the issue, from the breaker panel to the condenser, I measured and it's about 75 feet give or take.

Our home is about ninety feet wide. The distribution panel is in the garage, at one end of the home, the A/C is on the opposite end. Thus the wiring run is at least 100 ft., if not more.

Not a problem.

quote:

Originally posted by Excam_Man:
Wrong, 10/2 with ground. Two hots and a ground.
There is 18/2 for the control wiring... 24 volts to operate the contactor.

Still see no issue with the wiring.

This ^^^^^

My vote is for noisy contactor or possibly a failing motor start capacitor.

quote:

Originally posted by PASig:

quote:

Originally posted by selogic:
Could be the contactor . They usually operate on 24 volts and that's a long run for that low of a voltage . Smaller wire too .

I do not see any wiring like that running out there, just the main power cable which I realize now is most likely 10/3 and not 10/2, right? 240V? Two hots and a neutral?

It’s more just an annoyance to me.

The wire is 10/2. Most A/C compressors require 240v, so they don't need 120v. What you are calling the "neutral" is the center tap to the power company's transformer coil, which is how we get 120v in the U.S. I installed one using 10/3 once, but that was because it was the only wire I had on hand at the time, and I didn't want to make a trip to get more 10/2, but the compressor only uses 240.

Like Excam_Man said.

Was you able to grab any of the specs?

.

quote:

Originally posted by Excam_Man:
Was you able to grab any of the specs?

I will try and get that later today, I got sidetracked on this whole issue.

Sitting on the back burner during Winter...

quote:

Originally posted by Excam_Man:
Sitting on the back burner during Winter...

Maybe he's waiting on the second mortgage to go through so he can afford the wire.

Sorry, I’ll see if I can get those today sometime. I’ve got 3 young kids and it’s easy for things to fall by the wayside with how busy things get.

I did noticed that the installer seemed to reuse the “whip” (I believe that’s what it’s called) from the original AC unit that was there from 1989/1990 to 2018. Could that possibly be part of the issue?

If you purchased a system with a scroll compressor, you may hear a buzzing noise on start up. The exact reason is difficult to envision. However, the scroll compressor, with its four moving parts, can make unusual noise. We had to engineer means to prevent reverse orbiting of the orbiting scroll to eliminate shutdown noise.

My Daikin system with a Copeland (now Emerson) scroll compressor has a buzzing sound on start up.