I have a 1986 190e.

My problem:

I used to get all heat all the time. Now I get no heat at all. Does not matter what the control panel is set to. Also, the control panel temperature "wheel" does not regulate/change temperature.


What I've done:

Replaced the control unit with a used one that is supposed to work. No change in problem above.

Replaced heater control valve at firewall. No change in problem. BTW, I am not getting vacuum at the heater control valve, which means heat should be on all the time.

I am getting some vacuum at the vacuum control "junction" located to the right of the glove box. Also, fan is turning at same location which, I believe, goes to the temperature sender in the ceiling.

Request:

Advice? Diagnosis? What would cause the heat to all of a sudden go out and not heat anymore? Heater core? Aux water pump (is that what it's called).

This problem just happened one day this week. After all changes I did above, car still blew only heat (not a roblem now since it's cold out) but I want to know why I'm getting no heat now. Thanks!!