I recently bought an 86 420 sel.

The heater does not work, unless the car has been completely turned off and started with the heater on. Then it only blows heat to the front. The back vent blows cold air. If the climate control temp is touched or any of the heater option buttons are touched then the heat stops, (and I get cold air.) The fan setting have no impact on any of the above.

To get the heat going again, I have to turn the car completely off and wait a few minutes befor starting again.

I have searched the forum and not found a problem exactly like mine. The closest I got was to rebuild the monovalve. Would this do it?

Also, if I need to get at the climate contols how do I pop the wood face off?

-D Rider

you can have numerous issues. bad fuses. if they are old just replace them all. use only ceramic copper fuses.
the heater mono valve is bad. the pushbutton control unit has cracked solder joints. the small hose from the dash temp sensor to the fan is bad. the fan is bad. try those first.

george