A/C Problem--stops working at highway speeds

[Upset99]

I dont get the car much on the highway but when I do, I experience a problem. At about 70 MPH, the A/C stops blowing or down to a trickle. If I let off the gas a little, the A/C starts to blow but will stop again. It seems that if I want the car's A/C to run well, I must drive about 65 MPH.

Ideas?

[superbad]

I get that too, but only on a long hill when the car is under boost for an extended period of time (swamping the manifold vacuum). The heater control valve is vacuum operated, and I think if you lose vacuum, it opens up and lets coolant go to the heater. You might have a slight vacuum leak somewhere.

[Upset99]

thank you...that sounds right

[Andy_J]

Not sure if it is the same with the Elan, but the Cartlon shuts the aircon off over 150mph to aid acceleration