Don:

Sounds like you have a bad pushbutton control unit, or bad actuators.

The only way to test is to attach a vac pump to the heat actuator and see if it holds vac. If it does, the PBCU is bad, get another one. If it doesn't, replace the actuator (this one, at least, is easy to get to.

It is possible for the actuator to have a leak and still work, but that shouldn't kill the rest of the vac system.

Do your locks work with the car off? ACC off, or on? If the locks don't work with the car off, or they fail when you select heat, I'd suspect there is more wrong with the vac system.

You should probably blow the $40 on a MitiVac hand pump. I suspect you will find that you have lots of bad vac connections in the engine compartment and have low vac supply along with a problem with the ACC.

When you get the pump, disconnect the green vac line in the engine compartment and pump the system down with the hand pump. Must hold vac. Big leaks will be obvious. If you hear leaks at the pushbutton control unit, replace it, not really a repairable part. Good used one should be around $75.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!