An office has a 2.5 ton Trane R-22 10 SEER condensing unit and a fixed orifice metering air handler, both installed in 2001. The office is a ground floor unit of a two story building and the condenser is on the roof of the structure. The space cools as it should, but when the compresser starts, a buzzing sound can be heard from the circuit breaker panel. The buzz is usually less than a second, but sometimes can last 1-2 seconds. The owner said this has been happening, on and off, since he took the space (2002). I was on the roof near the compressor when it started and did not hear anything unusual. However, there is definitely a buzzing sound coming from the breaker panel.
The owner says the breaker has been replaced and the wiring to the unit has also been replaced, both of which seemed to be the case when I checked. The connections also seemed tight. Also, according to the owner, a hard start kit was connected and then removed, the condenser fan motor was replaced, gas was added and removed. I'm sure other "service" was performed as well.
What kind of electrical problem could this be?