Morning,

The climate control unit puts out hot air only. Turning the temp control wheel down to blue has no effect on the tempetature. Also, the vent flaps do not work. I can see how the vacuum would make the flaps work, but I just don't see how the vacuum could be used on the temp wheel to set the temp. Tomorrow I'm going to start working on this after thinking about it for a couple of years. I know that either my ccu is shot, or a vacuum leak is somewhere - I'd just like know about the temp wheel before I start.

Hugh Sr.

1984 190d (W-201) 122,047

I'm not TOTALLY understanding of the W201 controls, but I understand that the heat control valve on this vehicle is vacuum operated. NOT electrical like other MB's...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

If the CCU is bad, it can't send an electric signal to close the monovalve/heater control valve which is normally open. I'm not saying the car in question has electric or vacuum control, just saying that a bad CCU can be at fault if the valve is electric.

Sixto
87 300D

If i remember correctly, the CCU goes in to a fail safe mode when it sees that there is a vacuum leak some where in the system or if one of the components is behaving abnormally.
In fail-safe mode, I think it only gives out heat and that too through the defroster in the dash . Its to make sure that your wind screen does not fog up under any circumstance.
The areas you should look at are the dash pods. The dash pods get their vacuum through the vacuum control unit. You ask what the heck is Vacuum control unit ? Well, its the thingy behind the glovebox that takes its signals from the ccu as to which vacuum pods to send vacuum to and then send out vacuum to the said dash-pod to acutate the flaps to divert air.

The best way to see if there is a leak in your system is to access the vacuum control unit behind the glovebox . All the dash pods get their connection from it. You can take off vacuum tubing one by one and test with a mityvac to see which ones are the offending circuits. At the current age of the car, i think all of them will be the offending circuits.

So , good luck and happy reading. there is a ton of stuff on this forum and you can always post back here . I had to go through a lot of trouble shooting to figure out what was wrong with my CCU and vacuum circuits.

__________________
1987 190D 2.5 Non-Turbo , automatic
Currently fixing : diagnosing vacuum functions,
, fuel leak at injectors, Dash Re-covering , speaker replacement with aftermarket amp and new wiring, generic keyless entry system .

Future projects :, antenna , Transmission modulator pressure adjustment or replacement... more to come...

Fixed : Windows, Ground wiring cleaning, random transmission kick-downs.

Don't rule out the improbable. My climate control was working perfectly after I re-routed the vacuum someone had tampered with, and then it just stopped working. I had both electrical and vacuum problems at the same time. I'd check CCU and vacuum related components both.

__________________
[/SIGPIC]~cirrusman

1983 Mercedes Benz 300SD - Wife calls him "Chitty Chitty Bang Bang"
[SIGPIC]




1983 Toyota Tercel (Tommy, The little Toyota that could)
1965 Ford F100 (Grandma Ford)
2005 Toyota Sienna (Elsa, Wife's ride)


Gone:
1988 Toyota Pickup
2004 Subaru Outback

1987 Cadillac Fleetwood Brougham
1986 Volvo 740 GL Station Wagon - Piece of junk.
1981 Volvo 242 DL 2 Door - Hated to see it go. R.I.P.
1987 Pontiac Fiero GT

The two most likely problems are the one mentioned in the post above, of a leak in one or more of the pods controlling the flaps, and a problem in the CCU. The usual problem for the latter is the solder joints on the circuit board.

The system is complex. Here's the best write-up for this system on the W201 description and troubleshooting:

Troubleshooting the Mercedes-Benz 190 Tempmatic ACC Climate Control System

When I test the lines on the vacuum control unit how much vacuum should there be? I've got a Mity Vac, but it's been several years since I've used it. When I put it on a vacuum line vacuum should show up on the dial without me doing anything - right. I do appreciate the responses I got. Thank you.

Hugh Sr.

1984 190d (W201) 122,047

Are you using the MityVac as a gauge or as a vacuum pump? Gauge readings aren't very useful in the ACC system with the engine running because the engine vacuum pump can maintain 20"Hg along the supply line even with leaky actuators.

Each actuator pod should hold at least 12"Hg indefinitely. That's not a spec, that's my conclusion based on what I've read. Note that some models have junctions and such between actuators so mind where you test. The line leading from the vacuum source to the vacuum switching valves should also hold vacuum indefinitely with the engine off and key out. Losing vacuum over, say, 10 minutes isn't reason enough to tear into the dash, IMO.

Sixto
87 300D