Rooftop RV air conditioner fan doesn't blow when turned on

i would say its the relay board or communication cabl between stat and board.

thermostat or relay module

Can you hear the compressor starting? If so, suspect broken pipework and loss of refrigerant. If not, suspect loose wire to compressor or thermostat

If there is no air moving when you turn on just the fan the fan control sw, connections to the fan, or fan motor is bad

Have fan start capacitor checked/replaced by licensed tech, or electrician as they are very dangerous to work with if not experienced and can give a very high voltage shock, that could be fatal. They basically store and increase voltage to higher range for start up of fan and compressor.

Check fan relay. Fan capacitor

Sometimes the fan stays on a little longer to cool the motor down before turning completely off.

sounds like it is miswired. actually try fan on with the heat on and see if the fan works.

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See if helping the fan turn will get it going thrn let it run awhile.. The fan motors rake a set if not used often enough.

soiund like a relay going out or a shorted wire.