Hi all.

I've got a '93 190E with the popular max-heat, default condition with hot blowing out the sides and dash. I've read every post I can find on the subject for 201s and 124s, but I can't find any single post which lists the sequential things to check, so I'm asking for assistance from someone who's had this before.

The condition appeared a couple weeks ago. I thought the cheapest, easiest fix was the heater control valve under the cowl by the wiper. I changed it today, but it had no effect. Playing with the extracted one, it still opened and closed normally when I applied 10-20 psi orally (no flames please, my benz is a girl). So I don't think that was the problem. 12 years and the thing still worked fine. It was a 16 dollar dart so I thought I'd try it.

I don't think the vacuum delivery to the top of the valve is functioning. The line seems to hold pressure, but I don't think there's any vacuum actuation created. I tested the new valve with the vacuum line disconnected from the top, and the lever freely moves open-closed, open-closed. When I attach the vacuum line, the movement of the lever is restricted, which leads me to believe the line is pressurized, but not sucking when it needs to.

Another thing that's weird, I let the car run today and manually held the heater valve closed, for like 3-4 minutes, and the side vents still blasted hot air. I would have expected them not to, with the valve closed. Maybe this isn't a valid test?

The a/c system on this car has been shot for about 3 years, with a coolant leak somewhere, but I don't know where. I'm fine with no a/c when the alternative is a couple/few dimes to fix. Chicago is hotter than hell but usually only for 2 months, then it's back to cold. Hopefully, correcting the max heat can remain independent of the faulty a/c.

Can one of you climate control or vacuum experts give me some ideas for the next couple things to check?

Thanks in advance for any assistance.
Mike. Just turned 156K...badge time.

__________________
1993 190E 2.3 California