I have an older E300 (1986) and my A/C wont come onif the engine is hot. Sometimes if I turnthe ignition off and on again it will work but most of the time no. If the A/C is working I can drive all day - it wont quit when the car is running but if I stop and turn off the ignition I can be sure it wont work when I start up again (or until it cools). Does anyone know what might be causing my problem? PS: I live in Phoenix where A/C is critical. Thanks