Good morning HVAC Forum,

I have a Focus here making me scratch my head and hope someone is familiar with the system. Customer left car saying the AC would get warm then cold but would not keep the cabin cool. I first cranked it and turned the AC on and the compressor came on with the fans so I left it for a few while I finished up another one. Came back to it about 10 mins. later and all was good and cold. Low side sweating good and 45 deg air coming out the vents. So far so good. Went to drive it and as soon as I pulled off the lot, the air warmed a little then cooled back down. I then noticed it did the same thing as soon as I let off the accel and slowed down. By the time I got back to idle it was cooling down again. Hm... Got it inside and hooked up the gauges and all looked good at 220/40 H/L side. As soon as I pushed on the gas pedal fast about halfway the compressor cut out. I then slowly accelerated to about 2500 RPM and all was good but as soon as I let off the compressor cut out again. Knowing this car had both a dual pressure switch and a low pressure clutch cycling switch, I decided to eliminate them one at a time. Jump across the low pressure switch and still had the same deal so I pulled the diagram and jumped both sides of the dual pressure switch. Exactly the same... So I left those 2 switches jumped and went to the relay box. The PCM grounds the relay to engage the clutch. What I found was that even with the 2 pressure switches jumped, the PCM would take the ground away from the relay anytime I would rapidly change RPM either way.. If I punched it down halfway or more or released it from 2500 or higher, the ground would disappear and come back 4 or 5 seconds later. So here's my question: Does the PCM use any other info to decide to disengage the clutch. It's not like the old WOT cut out of years past but seems to be any rapid change in RPM or TPS position.

Any thoughts at all would be greatly appreciated.

Mont

Mont Winfrey
Owner/Technician
Automotive Diagnostic Services
Rosemark, Tennessee, USA