Tim9712v

Is the obvious answer the Compressor clutch is slipping at higher RPMS? My AC blows ice cold driving around town, but at speeds above ~60mph it blows luke warm (probalby 75degrees or so) when ambient temp is 85.

Truck has 4.10 gears and I cruise around 2500rpms on the hwy at ~75mph

What gives?

Thanks in advance!

Andy505

Blend door maybe?

TheWaterman1000

Have you check AC pressure? Low coolant? One test I do Is short the control plug at the condensor near the fire wall to see if compressore is running right.

patdaly

Would be my first thought as well.

When it is setting idling and the AC on, does the clutch cycle at all?

Tim9712v

I can sit in my driveway idling all day long and AC is ice cold. If I drive down the highway at speeds above 55-65 or so AC blows luke warm

eng208

Probably blend door. Check vacuum on the mixer and see if it is adding warm air under slight load.

patdaly

As the engine RPM increases, the volume pumped is also increased, lowering your low side pressure. If it is right at the line, you could have the low side switch dropping the compressor out. If it were a vacuum issue, I would also expect it to send the output of the unit to defrost as well as moving the blend door. I don't see you noticing the output location changing.

I would get a set of gauges on it first.

chariotdriver

Let it warm up; set the parking brake, tranny in neutral or park; then have a friend rev it up to 2400 rpm and see what it does. The compressor clutch may be slipping at high rpm, you can clean it with some electric contact cleaner which is plastic safe and no residue if you see any kind of comtamination on the compressor clutch hub. It's one thing to get the compressor spinning at idle compared to high rpm. Just a thought but it really sounds like you need to dump some more refrigerant in the system.