I’ve recently gotten my 98 f150 running after it sat for 2 years. The ac worked fine for the first couple of days and then started having a problem like someone turned off a light switch. The ac will blow cool to cold air on the low setting only. If I change the fan speed to a higher setting it blows warm air. If I go back to low it still blows warm air. I can turn the system off for a few minutes and then the low setting will blow cool again. The compressor is running and the clutch is engaged. Can anyone steer me in a direction if they have experienced this before?

 

Get someone to check the suction and discharge pressures. If they are proper, that means the AC is fully charged and the compressor is doing its job.

 

Sounds like a busted blend door flopping around if the reported observations are accurate. Double-check the compressor observation and the temperature of the inlet/outlet lines during a "warm output" interval.

 

The discharge pressures when not running equalize at about 80psi. The discharge pressure when running on maximum fan and ac are35 on the low pressure port and 190 on the high pressure port.

 

Those pressures should be good. Start looking at the blend doors.