I just finished replacing the heater blower motor in my 1984 190d. While doing that I noticed a red vacuum line that runs through the firewall on the drivers side over to passenger side where it is attached to a round something on a heater hose. My car blows only hot air throught the vents, and the flaps do not work. From what I have been able to find out so far is that I might have a vacuum leak. It's not the climate control unit because I just replaced that too. I took the red line off the round thing and checked the round thing for vacuum - it holds vacuum. I checked the red line for vacuum and the vacuum slowly decreases. When I cranked her up my Mity Vac did not show any vacuum on the red line. Does this mean that I probably do have a vacuum leak somewhere in the climate control vacuum system? Thanks

Hugh Sr.

1984 190d (W201) 132,432

Check the yellow check valves above the brake booster, they disintegrate over time.

Honestly, 30 years later, you're 201s vacuum actuators are most likely suspect.

I went through my 87 W124 and changed them all, of which all but two were shot.

The easier way to find the leaky circuit is to one by one from the vacuum switch block behind the glove box, pressure check (negative pressure/vacuum) each line individually, I'm sure you'll find several that won't hold, which means the dash comes out.

If the gods of good fortune are looking down on you, maybe a line is off, but that's a long shot. Start in the engine bay and work into the car, the yellow check valves I mentioned are cheap and readily available and like I mentioned disintegrate over time, then move inside. If the supply side is tight, which goes from the check valve on the line to the brake booster to the vacuum switch block, then the leak is inside.

PS the round thing is a vacuum accumulator to buffer the variations in negative pressure, if it had vacuum, you're good.

The port at the vacuum pump on the front of the engine is capable of about -14PSI, which you should be able to read from every point in the system with no leaks.

The fact that you're not complaining about the engine doesn't shut off AND you said there was vacuum on the red line to the accumulator tells me your leak is inside, ESPECIALLY if it only blows hot.

There is certainly a vacuum leak. The red line is connected to the valve for the heater core. Pulling vacuum closes the valve so with a leak the valve is always open and coolant is always flowing through the core.

From the check valve the red line with a stripe goes to the vac reservoir, check it. Then the green line supplies vacuum for the climate control system. Both the green line from the check valve and the red line from the heater valve are connected to the vacuum switchover, along side the glove box behind the vent outlet.

Since you have already replaced the control unit and the blower, I know where this headed. All of the rubber connectors have hardened over the years and just pulling them to check vacuum will make them leak more. Removing the dash is no more complicated then getting at the blower motor, just a lot more stuff to get out of the way and a lot more fragile plastic.

There are four actuators and a host of connectors to replace once you are in there but it is not that complicated. Once completed you will have a fully functioning climate control it is worth it.

__________________
Charlie

85 2.3-16 ECE Track Car "Connie"
86 2.3-16 Slushbox Devils Stepchild. "Red"
89 2.5-16 ECE. Bimmer Eater "Sophie"
02 ML 55 Towmeister "Gertie"

Hugh--

The attached diagram is from the 201 climate control manual--which incidently is available on startekinfo for FREE!! if you can believe it.

Work through each circuit from the switch block and you'll find your leaking line(s).

This link is to the entire manual, a must for that car and your sanity.201 Star Library

Attached Files

Vacuum Circuit_201.pdf (123.3 KB, 121 views)

Thank ya'll very much - your comments have really helped me out. Now, I wil walk out in the warm sun and smoke a cigar to see where I go from here. Thank you.

Hugh W. Smith, Sr.