Gas and Oil Home Heating Furnaces - heat pump noisy in defrost mode

The outdoor coil of our heat pump, (located outside of our bedroom window) is extremely loud when defrosting. The hum is cylical for the 1st 10 minuites, then, after hearing what sounds like pressure relief in the system, the hum becomes constant and lasts another 5 minutes. The HVAC contracor (hired by our home insurance co) who came out first replace the fan motor (which of course didn't help) then said everything was OK and these things tend to be loud. He didn't hear it in defrost mode. It's not a little loud, it's VERY loud, and I need the insurance co to fix it. Can you help?

borba:

In order to diagnose your problem, one would have to hook-up a set of guages on the system.

Unfortunately we are here and you are there.

If someone paid the tech for the motor change, he should be called back.

Sounds as though the system is overcharged with freon, but it could be something as simple as dirty air filter or dirty outside coil. The relief valve you hear is a bypass valve in the compressor that comes into play when pressures in the system get to high.

One of the loud noises we hear all the time in the field can best be called a chattering contactor.Sometimes you hear it loudest because the fan stops turning during the defrost. Make sure you have 24VAC at the contactor coil though because sometimes long runs of wire will cause excessive voltage drop. A tech should be able to find this easily though, problem is, sometimes the customer gets ripped if you replace them, thinking they are trying to sell him something he never needed, it worked before.
The pressure you hear is from the heat pump, and is normal. The reversing valve is running the unit in AC mode temporarily to defrost the outdoor coil and the outdoor fan will be off and you may see a steam cloud. The indoor air handler runs with the electric strip heaters on to temper the air.
The defrost cycle is done every 60-90 minutes depending what the unit is programmed to do,...