190e 2.6: Cold eng., cold a/c, warm eng., warm a/c
 

I suspect that heated air is getting in and mixing with the cooled air. (The a/c system seems fine; condenser works, plenty of charge.) This car does not have the monovalve, the failure of which would have explained this failure on other cars. I've searched on here and can't figure out how this mixture works on this car, or where to find the valve or other device that controls it. Thanks in advance for help!

The car is a 1991, though I doubt this matters...

At first I thought it strange that a 103 motor had no monovalve. I then looked up the heater valve for your car and sure enough.

Look at the photo of it below. Picture on the left has what appears to be a vacuum hose connection on top.

Vacuum issue or perhaps the valve is defective? Just my 2 cents.

http://catalog.eautopartscatalog.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1U40N9POF1UI0W5PAW&year=1991&make=MB&model=190-E-005&category=R&part=Heater+Valve

Yep check the heater valve. It is located on the passenger side under the debris screen under the wiper.

Great, thanks!

190-heater valve
 

now that you know where the valve is,first get a hand crank vacuum pump and attatch to vac conn on valve.see if holds vac.if not replace.if it holds leave pump attached and drive car to see if problem cured. if ok then you will find under glove box a set of vac valves that controls all of heat and ac.once you establish that good vac is coming into valve set you will need to replace valve set.they cannot be fixed. david poole e.p. dallas tx.

And I have a nice brand new one in my tool box that I never needed. Let me know when you are done testing if you want it and I will send it too you for a few bucks.

Which?
 

Jamie,

Do you have the valve set or the heater valve in your tool box?

I have the heater valve still in the packaging. I also have an old valve from under the glove box that I am not sure if it is good or bad. I replaced mine and my CC Unit at the same time and it fixed my issue, which was my aux pump not turning on and my heater valve not closing. I am thinking it was the CC unit since the pump worked after replacement. I had just changes the vacuum distribution unit while I was in there. Not taking any chances at the time. If you need it for testing or to use you are more than welcome to it for the cost of shipping to you. The heater valve is your for 10 bucks if you need that.