Center air vents - PeachParts Mercedes-Benz Forum

Stevo · #1 08-11-2002, 01:37 PM

The two center vents in my 85 240d do not seem to supply much fresh air. I do have AC but no climate control. The slider control in my 79 240d really lets a good amount of air in but NOT so on the 85. I have searched the archives without result and am assuming it is a mechanical system w/o the use of vacuum actuators. Could the ducts be plugged or are you just expected to crank up the AC for fresh air? Any advice would be much appreciated Thanks

psfred · #2 08-11-2002, 01:44 PM

I believe that there is a vac switchover on the 240D that switches from outside air to recirc when the AC is on. If you don't have adequate vac, the flap will stay part way open. This is true if the AC uses outside air, but has a recirc provision. If it is stuck in recirc, you won't get much outside air.

You can test by switching the ignition on, but not the engine, then engage the AC with the temp dial -- if you don't hear the flaps moving when you switch on and off, you either have a vac problem or a bad swith or servo.

You can test in integrity of the vac system by trying to pump down the green line in the engine compartment -- if it won't hold vac on the passenger compartment side, you have a leak. If it works properly with a hand pump suppling vac, you have a vac supply problem or leak in the supply side.

Make sure the slider is actually attached to the flap, too -- I have to manuall open and close the one in the 220D, it's broken off.

Peter

Stevo · #3 08-11-2002, 06:32 PM

Peter
Thanks for the reply. I went out and turned the ignition key as if the engine was running then moved the AC adjustment wheel and there was NO noise as in flaps moving , nothing too be heard. The PO had just spent almost $800.00 on the AC and I was thinking maybe they screwed something up but this switchover thing would be under the dash and they wouldn't have messed with anything under there I think? So what you are saying is that the AC would use this vacuum switchover to bring in outside air (open) or recirculate inside air (closed) and the vent is at least partially closed so when I just want fresh air (w/o AC ) , No can do? I need to invest in a Mity Vac and check out the green line then.

Thanks again for your help

psfred · #4 08-11-2002, 07:06 PM

I certainly remember some flaps moving when I tested the AC in 1983 240D with manual AC. There is also a lever on the center vents, I think (maybe not) that closes off the outside air. There is on the W115 chassis, but that doesn't mean much.

You should be able to get unconditioned air out of the vents, and if nothing comes out unless the AC is on, I'd suspect the vacuum system. Check to make sure the green plastic line up by the brake booster isn't loose, then get a MitiVac or similar hand pump. Very difficult to apply that much vac by mouth (and not recommended!), but you can also use a pump intended for AC evacuation -- it will be too strong, but at least will let you know if the sytem holds vac. If it leaks down, you will have to look under the dash for the leak. If it works with external vac, you need to find out why you don't have enough.

Peter