Ranger AC blows hot air on highway

[MrHawk]

Ford Ranger has new compressor and pressure has been tested by a Ford Mechanic. The air blows cold during city driving and at idling. However, on the highway as soon as the temperature gauge goes slightly above middle it blows hot air. Once the temp gauge goes middle or below cold air comes back.
Any suggestions would be appreciated.

[freedom5]

Originally Posted by MrHawk

Ford Ranger has new compressor and pressure has been tested by a Ford Mechanic. The air blows cold during city driving and at idling. However, on the highway as soon as the temperature gauge goes slightly above middle it blows hot air. Once the temp gauge goes middle or below cold air comes back.
Any suggestions would be appreciated.

If it has an accumulator there is a pressure switch mounted at the outlet. If so the compressor clutch circuit goes through this pressure switch. You can disconnect the plug on the pressuer switch and put a jumper across the terminals then test drive it. If it works this way - replace the pressure switch. It's rather inexpensive and you don't have to blow the charge as the switch has a schrader valve where it disconnects.

[--weezl--]

there is also, on some models, a valve that blocks the coolant flow to the heater core, it allows coolant to go through the core when the heat is on, and blocks it for ac, it is vac controlled, this might also be your issue...

i would say if the above test proves fruitless, check that out... might be stuck open, or partially open...