A/C problem - PeachParts Mercedes-Benz Forum

kchemers · #1 08-24-2010, 01:57 PM

89 300TE the a/c is blowing out of the side vents and the defrost. I have lost the center vents. I know it is a vacuum module, I don't know which one, location or ease of repair, any help would be greatly appreciated. Also if it is a buried module can I prop a stick in the center stack to hold the door open just like the 560's????

jcyuhn · #2 08-24-2010, 02:41 PM

Did it stop blowing through the center vent and start blowing through the defrost at the same time? If so, it's more likely you have lost the vacuum source which actuates the vents as opposed to any problem with the vacuum actuators themselves. Vacuum is used to both close the defrost vents and open the center vents via independent sets of actuators.

First step in diagnosing it is to pull the glovebox and expose the vacuum distribution block (on the lefthand side). Use a handheld vacuum pump w/guage (AKA Mityvac) to test each actuator - I think there are 7 lines. Also test the incoming vacuum source by hooking it up to the guage and running the engine; check to insure you have vacuum supply.

The individual lines from the vacuum distribution block are color coded; you can lookup the function of each using the search tool here - there are many similar threads.

Yes, you can block open the center vents by removing the louver assembly and using a prop rod or similar. But unless you also get the defrost vents closed, this is going to be of limited value.

Best of luck

kchemers · #3 08-24-2010, 03:01 PM

actually it stop blowing from the center vents and switch to the defrost at the same time, also my vacuum gauge on the dash is pinned to the right. is this all an indication of lost vacuum?

kchemers · #4 08-24-2010, 03:02 PM

if I dont have vacuum supply then what is my course of action?

Cal Learner · #5 08-25-2010, 06:57 AM

Trace the vacuum lines until you find the leak. Repair.

jcyuhn · #6 08-25-2010, 09:51 AM

Quote:

Originally Posted by Cal Learner

Trace the vacuum lines until you find the leak. Repair.

the above statement pretty much sums it up. My bad memory says the vacuum supply line is green - maybe with a white stripe? - and goes from the distribution block behind the glovebox to a set of connections near the brake master cylinder. I'd suggest you start looking there.

I don't know how the engine economy guage works, so can't say if there's any possible connection. I kinda doubt it.

ps2cho · #7 08-26-2010, 04:01 AM

The economy gauge is connected to the same vacuum cable as the vacuum pods are. So yes it could be connected, or in this case...disconnected.

The vacuum line runs from the bottom right hand corner nearest driver fender of the intake manifold. The line runs up through the engine firewall above the ABS into a Y vacuum connection. One for the vacuum pod unit behind the glovebox, the other to the cluster.

My bet is either the Y connect has come undone, or the one at the intake manifold.

jcyuhn · #8 08-26-2010, 10:50 AM

Quote:

Originally Posted by ps2cho

The economy gauge is connected to the same vacuum cable as the vacuum pods are. So yes it could be connected, or in this case...disconnected.

The vacuum line runs from the bottom right hand corner nearest driver fender of the intake manifold. The line runs up through the engine firewall above the ABS into a Y vacuum connection. One for the vacuum pod unit behind the glovebox, the other to the cluster.

My bet is either the Y connect has come undone, or the one at the intake manifold.

That's great input - I've never owned a 124 with the economy guage. I think he has a simple repair ahead of him.