A/C only works at idle
 

Helping a buddy with his '17 Winnebago with the v10 f53 Chassis.

Back story:

He bought it and it would blow extremely cold to the point that after 30 min, the coil would freeze up. After stopping the engine, it would thaw out but it would not thaw by simply turning off the AC.

Took a look under the rig and noticed that the clutch was never disengaging on the compressor. took out the center bolt and tapped on the clutch and was able to work it free. It looked to have been rusted in place. cleaned up the mating surfaces with some emery paper and reinstalled the clutch and at idle, all was well. pressures looked good and it cycled on and off and a decent interval and duct temps were in the low to mid 40's.


Now here is the kicker. If you increase the RPMs to say 1500, the clutch on the ac will engage for like 2 seconds and then immediately disengage... wait 10 seconds and it repeats.. the pressures will drop as the compressor never stays engaged long enough to bring them up and the vent temperature climbs back to ambient temp. slow back down to idle and it engages just fine, cycles as per normal and the temps and pressures return to normal.

Both the high and lower pressure switches have been replaced and the refrigerant load is per spec as he had it evacuated and refilled to factory levels.

It is as if something is telling the clutch to disengage at higher RPMs due to slipping or something non-pressure related.

Any Ideas? I hate to tell him to start shooting off the parts cannon since at idle, everything seems to be working perfectly and only fails when the engine RPMs and not system pressures are elevated.

This can be verified with a set of gauges, but we may not have them available.

It does sound to me like there is a restricted orifice tube. As long as the right amount of refrigerant can get through like at low RPM's it's fine , but when the demand is increased the system is starving for refrigerant.