ACC III Questions (and answers hopefully) - PeachParts Mercedes-Benz Forum

Tanksowner · #1 12-04-2011, 05:22 PM

I'm very picky on how my Mercedes runs, and the climate control is no exception. Over the course of the past year, issues have started to add up. Now it's at the point where I want them all fixed. Any insight on the following problems would be greatly appreciated

1. If I turn on the climate control from the minimum setting on economy and turn the temperature dial to max heat, it typically puts out lukewarm heat at best, even after waiting for more than 10 seconds, which is what the FSM stated was the time frame for the climate control to switch over. However, if I shut off the climate control, wait a few seconds and turn it back on, gobs of heat will come out. Same deal if I want only outside air without any heat. It just doesn't seem to want to fluctuate to the desired temperature automatically without additional prompting. I have replaced the CCU, a bad temperature sensor under the dash, and insulation tubing which connects the sensor to the blower motor housing. Naturally, I assumed that it would be all peaches and cream now, and I have to concede that I'm a bit disappointed that after all the time and money I've been putting into it, it is still acting this way.

2. The defroster setting, as I understand it, should only have air coming out of the dashboard and legroom vents when activated. However I get air out of the side vents as well. I didn't have this problem when I first got the car, but it came to the surface about 6 months later. I'm not certain if this is a vacuum issue or not, but I would like it to function as it should.

3. My center vents were working before I had my A/C system serviced back in the Spring, but now that flap won't open up. I'm not sure if something crucial got knocked loose besides a vacuum line in the midst of their service. I pulled the line (two lines connected up to a rubber T-connector) going to that vacuum actuator and hooked up a pump to see if it would hold pressure. I kept hearing a faint hiss coming from the center of the dash so that didn't jive too well.

I saw a thread on here about disconnecting the metal arm from the air flap and using some kind of retainer to keep the flap open. Any advice about doing this job would also be welcome. I don't want to give up just yet, but I'm 24 and I admit, I'm also a little impatient. Not a good trait to have when working on an old car. Please help!

tangofox007 · #2 12-04-2011, 06:56 PM

Quote:

Originally Posted by Tanksowner

The defroster setting, as I understand it, should only have air coming out of the dashboard and legroom vents when activated.

How did you arrive at that conlcusion?

Don't you think a little defrost air on the side windows is a good thing?

Quote:

Originally Posted by Tanksowner

I saw a thread on here about disconnecting the metal arm from the air flap and using some kind of retainer to keep the flap open.

It could be that the arm has already become disconnected. And that is what is causing the problem. Tha arm connects to the flap with a plastic pin, which tends to break after 25 years or so.

Tanksowner · #3 12-04-2011, 07:09 PM

Quote:

Originally Posted by tangofox007

How did you arrive at that conlcusion?

It could be that the arm has already become disconnected. And that is what is causing the problem. Tha arm connects to the flap with a plastic pin, which tends to break after 25 years or so.

FSM says that max heated air will be routed to windshield. I assumed that it meant air would be going to only the windshield. Did I assume wrong?

The metal arm is still connected. It took considerable force to even pry the center flap open.

tangofox007 · #4 12-04-2011, 08:10 PM

Quote:

Originally Posted by Tanksowner

FSM says that max heated air will be routed to windshield. I assumed that it meant air would be going to only the windshield. Did I assume wrong?

You did. There is no automatic mechanism to limit the flow of air through the side vents.

Tanksowner · #5 12-04-2011, 08:24 PM

Quote:

Originally Posted by tangofox007

You did. There is no automatic mechanism to limit the flow of air through the side vents.

Okay then. Good to know. Thanks Tango. Got any insight to the first problem? That's the one that's getting to me the most.

tangofox007 · #6 12-04-2011, 08:40 PM

Quote:

Originally Posted by Tanksowner

Got any insight to the first problem? That's the one that's getting to me the most.

The detent positions on the temp selector essentially override the temp regulator by mechanically switching the monovalve ground circuit open or closed. Selecting the "Max Heat" position should immediately open the monovalve and provide max heat almost immediately. I don't see an obvious cause for the situation that you describe.

Tanksowner · #7 12-04-2011, 09:07 PM

Quote:

Originally Posted by tangofox007

The detent positions on the temp selector essentially override the temp regulator by mechanically switching the monovalve ground circuit open or closed. Selecting the "Max Heat" position should immediately open the monovalve and provide max heat almost immediately. I don't see an obvious cause for the situation that you describe.

Yeah neither do I. It may be a mystery that my mechanic will have to solve for me, but I don't have the funds to make it happen. I suppose I can ride it out for now. Since winter's here, and I know I can get heat SOMEHOW, it's not a huge problem. But it is definitely something I want to solve in the near future.