Foretravel Owners' Forum For owners and Fans of Foretravel Motorcoaches September 13, 2025 ...

Were the condenser fans on?  If not, high side pressure could reach extremely high level and on many systems cycle off the compressor.

I wonder if its just not fully charged.

My money is on needing several more cans of refrigerant.

It would be helpful to see what the guage readings are while it is operating. If as you said the low side guage goes very low then the low pressure switch would shut off the compressor, which would indicate a restriction to me. Possible partial blockage of the expansion valve. Of course the thermostat could be bad as it has a probe into the evaporator core.

You can check if it is causing the 12 volts to stop coming from it when the compressor stops or if it is still allowing the 12 volts to flow. If it has 12 volts on both terminals and the compressor shuts off you know that is not the cause of the shut down. The thermostat is under the dash.

Some of the things that can make an air conditioner less efficient can be something as simple as dirt on the condenser or evaporator fins.  It is also important to have the correct amount of oil and refrigerant in the system.  Too much refrigerant effectively reduces the size of the condenser as liquid refrigerant will fill up the lower portion of the condenser.  Oil to some extent will circulate through the system.  Too much will coat the inside of the tubing in the condenser and evaporator reducing heat transfer. It can also collect in the dryer reducing refrigerant flow.  Not enough oil and the compressor wears out faster than it should.  One should not add oil just to be on the safe side, only when it is known that oil has been lost like replacement of a major part. Of course the system should be properly evacuated before refrigerant is added.  The condenser on my coach did not have a shroud for the fan.  Air was just basically being pulled through the center section of the condenser.  If you can work with sheet metal it is not difficult to make a shroud that positions the fan a little farther away (an inch or two) from the condenser and pulls air through all of the condenser.  Just be careful not to puncture any of the tubing with a drill or screw.  The box around the evaporator at the dash has doors to direct air flow, both inside and air from outside.  These doors can be operated by electric motors, vacuum motors, manually, and by other means.  They should be working properly and not stuck in a position that lets outside air in.  And as mentioned the heater should not have hot water flowing through it.  My coach has a switch for fresh air, blend, and inside air; however the door for that is either open or closed there is no blend position.  With blend selected the door could be either open or closed.  Other coaches may be different and work correctly.  Most of the time when the compressor cycles on and off it is usually low on refrigerant, but could be other things like a defective switch.  There should be a sight glass on the receiver/dryer located near the condenser on the liquid side.  There should be no bubbles in view after the system has been operating continuously for about 10 minutes and not cycling on and off.   You may need a mirror to view the sight glass on top of the receiver/dryer.  I'm not a refrigeration guy, just things picked up over the years.