I am trying to diagnose a situation where A/C works well most of the time but on hiway and towing it will fade out, turn it off for a few miles and then back on and it will work again for a while. I was a road trip so grabbed a quick fill can of R134 with a guage on it and it was showing normal but the compressor was not cycling at all, just on all the time.

I got back home and put guages on, with following conditions
blower on full, set on A/C (not MAX), windows open.
paramters are:
ambient 76F
vent temp 62F
Lo Press 43 psi
Hi Press 180 psi

The compressor is not cycling, on all the time, is it not getting to a high enough pressure?

Thanks

 

Recheck your readings with the RPMs around 1500.

Clarify your clutch activity. It should cycle on at 45 psi ascending and cycle off at around 22 psi descending.

Your high side pressure, at around 2.5X ambient temperature, is in the ball park. Your low side pressure isn't really low enough, however, that may be only due to low compressor speed.

Check your clutch gap, perhaps it's slipping.

Inspect for evaporator icing by looking for a large puddle of water under the truck when parked after a fade-out episode.

Steve