76 Dodge 440 model 821F ---roof air conditioning unit

My roof AC unit will blow air butdoes not cool.  What is usually the problem with these and the fix?
Thanks, Chris

[LARRY RAY]

MOST LIKELY THE COMPRESSOR IS BAD. IF YOU DO NOT HEAR A LOUD HUM WHEN GOING FROM JUST AIR TO COOL IT'S PROBABLY GONE. COULD HOWEVER BE A BAD THERMOSTAT SWITCH. IT'S JUST ONE OF THE THINGS YOU HAVE TO TRACE OUT. TURN IT TO COOL, WITH THE COIVER OFF THE UNIT CHECK THE VOLTAGE AT THE COMPRESSOR. IF IT IS 110 OR BETTER, BAD COMPRESSOR. CHANGE THE UNIT IT WILL BE CHEAPER THAN REPAIR JOB.