I’ve taken my 1985 300D Turbo to three different shops over this. My heater, when heat is demanded, throws out a great blast of hot air for 15-20 seconds, then abruptly switches to cold. So far, I have taken it to three shops. They replaced the mono valve (repair kit), climate control module, heater valve, and a relay...no change. I am taking it back in to the latest shop next week.
I’m not a mechanic by any means, but I did study a bit of A/C many moons ago. Armed with that, I did a bit of thinking about the problem. Here is what my puny little brain came up with.
Since heated air does come out, if only briefly, the blower is ok.
Since the temperature goes from hot to cold so abruptly, there must be some sort of damper in the ducting. Since there is automatic climate control, there must be some sort of thermostat to control the delivery of air to the cabin. That is likely the problem.
My question (assuming my little brain has it right) is: where is the cabin thermostat and can it be replaced?
Thank you in advance.