Trane XR15 NOISY Condensor unit Contactor

[BobL43]

In my other thread where I asked about running the Air Handler fan on Auto or on, I forgot to ask about the very loud Clunk the compressor contactor makes when it is De-energized. It is a little loud when it energizes too, but when it drops out: CLUNK!! I asked the installers and service tech about it and they said, yeah, every customer asks them the same thing.

I am in industrial automation, and have worked with high quality devices my entire career, but I've NEVER heard anything this loud either pulling in or dropping out.

What have the pros here experienced with this noise?

My condensor is Trane model 4TTR5049E1000BB, a 4 ton unit.

Thanks!

[SoFlaDave]

Haven't heard that complaint with an XR15. You may be hearing the compressor itself which can make a clunk at shutdown. It is not an indication of anything going wrong.

I have not talked to an engineer about it but when scroll compressors were introduced they had a tendency to run backwards during momentary power loss as the expansion of refrigerant pushes the scroll backwards and the rotation is continued by the motor. The clunk may be due to a design that prevents the scroll from doing this.