Our air conditioner unit turns on but just blows hot air

The fan is supposed to turn off. If the fan stayed on, it would feel like cooler air blowing, not warm air blowing.

either the unit is getting low on freon or filter and or coil are dirty

That question was originally posted on jul 3rd, 2012. Today is sept 11, 2017. What's up with that fixya.

Some of those old Mach 3's have a manual reset pressure switch, but you will have to take the cover off to find it. Most manual resets have a red button to push to reset. The unit may be low on refrigerant or the condenser coil stopped up with dirt.

COLEMAN R.V. AIR CONDITIONER SERVICE AND REPAIR QUESTIONS
COLEMAN R.V. PRODUCTS
GO TO rvcomfort.com
Click on RVP (RV PRODUCTS)
Click on type of AC, if you can’t find the information you want there,
then click on contact us on the Green Bar.
You can get Service Support or Email address and Phone numbers.

Make sure the condensor fan is blowing through the condensor on the roof. It sounds like the compressor is fighting high head pressures after running a bit.. After so many attepts, or if it suceeds in operating the load trips the circuit breaker.. Make sure the condensor is clean and air is passes through it from the fan. Just for clarifiication the condensor is the coil that gets hot and the evaporator is the coil yat create the cold air. Good Luck, and if you will, let me know how it turns out. Good Luck. Ned

Sounds like you have either a bad fan motor or a bad fan motor capacitor. When you turn the unit on with the fan not working, the compressor (the humming noise) runs and gets real hot real quick resulting in the compressor cutting off ( the nothing after) on it's inside high temp switch. This is what the compressor is designed to do so that when this happens, it does not burn the compressor out. Replace you fan capacitor, give the compressor an hour to cool, then try it. In most cases and if I'm correct, the unit will run just like you want it to. Good luck.
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Sounds like the evap coil is dirty or its low on freon.

The fins are dirty. They need to be washed every year or two with an acid based cleaner. They MUST be rinsed completely.

see if unit has a water level switch