I have worked and worked on this climate control til I am blue in the face.

History;

When purchases, found bad vacuum line on check valve, replaced. worked fine. 2 days later blowing hot air out the defrost all the time. Fan won't work, climate control computer seems to be dead.

action taken:
replaced the fan motor, climate control computer and fan speed selector. Still hot air out of the defrost all the time but now I have fan. Still no climate control computer working.
Replaced all four vacuum actuators. Now have fan, and AC everything seems to be working. Two days later back to blowing hot air out the defrost and no fan at all.
Pull the middle dash back out and found a mounting bracket for the lower actuator that controls the blend air flaps broken off.

Currently have no fan and the bracket is broken off the mount. Now I have to figure out a way to attach the mount back without permantly affixing the actuator to it where I can't get it off later.

Sorry, just had to vent. Any ideas why the fan stopped working AGAIN?

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89 190E
2.6L
Arctic white
Grey leather
Sunroof
Pirelli P400 rubber
Smoked corners

it seems to me that many links in the chain on your climate system are old and weak. there may have only be one link that was broken but when you fixed it the next weak link gave way. my experience is on a 380sl climate system so this is what I did:
with the glove box out and the instrument panel out i replaced all the vacuum tubing that controls flaps, also replaced all the check valves. tubing is cheap, even if you get the diff colored ones for each vent. so far total cost was around $18.
next came the actuator pods. all of them tested good with my-t-vac and held good vacuum for a few minutes.....except the one controlling the center vent. that one couldn't hold a jello vacuum, and that one is inside the heater box (means taking apart the whole dash to get at. since I can reach the center flaps with a wire hanger, i pushed the flap half way open and can live with a mild amount of air coming thru. by the way, that pod was held in place by two rivets, but the plastic housing around that area cracked so even if the pod held vacuum it is still just floating around loose.
I sent the push button unit to proforma in florida to have it rebuilt (resoldered) and now that works fine. cost = $135
same can be done with the blower control unit at similar cost. there is nothing else inside these units to break except solder joints.

still have hot air always? replace the monovalve. cost is $30 and takes 5 minutes to do.

by this time you will be very intimate and familiar with your firewall. tight places that made your hands ache with nicks and scratches will now feel roomy. and oh, yes...from time to time you will drop small metal objects and have side jobs of trying to find them, but thats another story.

People on this forum laughed at me when I said I thought MB's were "not as good as they try to make you believe". In one post for someone looking to buy a particular model, I wrote him to avoid all MB's. They're just too much trouble. Of course, all the purists started sending me death threats. People are just too strung out on their little 3 pointed star inside a circle. They like the feeling driving down the road like they're "better" than other people since they have a "premium car".

Ooooh, the poor guy with the lowly Toyota Corolla or Honda Civic. Driving down the road, perfectly cool in the summer with his ice-cold a/c, while the guy in the princely Mercedes is sweating a few pounds off, baking in his car, which probably has tinted windows on it, that he tells everyone "I thought it made the car look sharper". Ummmm, yeah, right. In reality, his a/c doesn't work and he's trying to stay cooler, but ... just ....won't ... part ... with ... his .... ego ... symbol, the MB.

Try this...... Contact MB. Tell them you are having major issues with it. Here's their strategy:

1) They'll tell you this is the first they've heard of a problem, like yours is the only one that was bad.
2) They'll ask if you bought new, so they can kind of make you think it was the previous owner's fault of not taking care of the car.
3) They'll ask if you've taken it "to an authorized MB dealership". Of course not, it'd cost you a fortune. They're trying to push the blame, like it was a lower repair shop's incompetence.
4) Tell them ALL MB's have a/c problems, and chronic ones at that. Tell them they'd be better off facing the problem squarely for the junk they sold us.

Call them just to see if I'm right.

Good luck with the a/c.