When the car has been in the shade when I start up, the A/C cycles on and off normally (usually), but when it has sat in the sun as today (it was 80 degrees here in Abilene today) it either won't come on at all, or it comes on when I start up and when it cycles off, it won't cycle on again. Turning the temperature wheel to max has no effect (it works beautifully for heat).
When it operates normally and I am at highway speed, it usually continues to operate normally.
Any ideas?