Re: 1991 164 No Heat At All
The hot/cold air is controlled by a motorised flap in the heater box. It could be that there's nothing wrong with the matrix but the motor driving the flap has stripped its plastic gears. The "stepper motors" are infamous in 164s. Unfortunately, it's a massive job (dashboard out) to change them. You should just be able to see the end of the temperature one (there's another one for distribution) through the little inspection panel inside the clove box. It pulls a little cable that you can just about see under the bonnet with a torch if you take the plastic cover off the heater box. Get someone to work the temperature control whilst you watch to see if it moves.
Also, no, the aircon doesn't need to work for it to blow hot air.