UFM82

2001 F150 S-Crew, 5.4l, 210,000 miles. A/C is misbehaving when running down the highway. It blows cold at idle. Pressures are 240 hi side and 27 low side with max a/c on and fan at full speed when idling in driveway, clutch engaged. Vent temp is 48. Once you start driving, the clutch cycles a lot and temps rise to 60+ at vent. If I get off highway and stop at light, temp drops again. Not had this happen prior to this year. Replaced fan clutch earlier this year for unrelated issue but bought Motorcraft part specified for truck so don't think that has any part of this. I have new orifice tube for truck but have not yet installed. Any thoughts?

rcairbear

Had a Thunderbird several years back that did the same thing- A/C tech said it was the filter/dryer- but he also changed the orifice tube also-so?? who knows...
but it worked fine after that.

R&TBabich

I wouldn't think it would be enough to cause this, but as the RPMs go up so does engine coolant flow.
Is the heater shutoff valve working?