Determine if the compressor is running. Do this by turning on the compressor and listening for noise and feeling for a vibration. If it doesn't run check to see if the thermostat is set correctly and make sure there isn’t a blown circuit.
Check the voltage with a voltmeter if the compressor is working. The voltage should be at least 13.4 volts. If the charge is below this it can cause the air conditioner to not cool.
Clean the air filter with a soap and water mixture or vacuum the filter clean. For the unit to work properly it must have proper air flow. If the air filter is dirty the refrigerant will not be able to pick up enough heat from the air inside the RV. If the condenser coils are blocked, it won’t be able to give off enough heat to the outside air as well.
Clean the evaporator coils by blowing them clean with compressed air. Neglected and clogged evaporator coils can prevent the unit from cooling.
Tape any rips in the duct work with duct tape. Any tears or holes will cause the unit to malfunction.
Clear the registers of anything blocking them.
