I had a callback on one already because the guy couldn't hear the outdoor unit switching speeds. On these units, the compressor has a solenoid inside it that opens or closes to control capacity. A properly installed unit makes no noise outside when it switches stages.
"We always fix it right the second time".
All posts are strictly my opinions and not those of my employer. I cannot make statements on behalf of my employer.
All advice posted by me is for educational purposes only, HVAC repairs should only be conducted by trained & qualified people.