RV repair guy installed new ac and it did exactly the same thing,fan came on no compressor.When I questioned him he said the compressor on the old unit was coming on.My husband thought he heard it too. Anyway,it took him two days to fix and he said the wiring in the old Dometic was not strong enough for the new Coleman even though they were both 15,000.btu. He strung new wiring from the new thermostat behind the wall into the breaker box and made a new breaker.It is working great so far.Not sure if I got ripped off or not but at least it's cool in here now and we are happy!