Throttle valve orifice in AC vacuum system? - PeachParts Mercedes-Benz Forum

smartin · #1 10-07-2004, 11:29 AM

In the 123 manual - "checking ac vacuum system" - the vac diagrams show a "throttle valve" in line (vac line) just before the recirc vac actuator - a couple of the other pods have them too. (85 300TD California) - By the way, my system does not have a check valve at the center vent actuator. Does anyone know the importance of this throttle valve. (It is a small plastic piece inside the rubber vac hose.

Thanks Steve

D.Blake · #2 10-07-2004, 11:51 AM

I rebuilt the vacuum system in my (now sons) 83 300SD. It had a brass restrictor in a couple of the lines to keep the vacuum actuators from acting too fast. Removing them may cause a large thump when some of the actuators operate. It may also increase stress on the mechanism. Not sure if your thottle valve is for the same prupose but it may be similar. Hope this helps.

smartin · #3 10-07-2004, 12:21 PM

I noticed that after I put it back in - but my problem is that the recirc flap will not go into recirc mode - it is always open (to allow fresh air in). When pushing button with both up and down arrows - it will move about 1 inch - then go back (fresh air). When you rebuilt your system, did you test vacuum system before you recharged it? I have already changed the change over valve for the recirc vac pod, no difference. I've replaced all hoses, compressor, condensor, dryer, sensors, vac pods - I am almost ready to get re-charge - but would really like to have recirc mode working first - Thanks

Help Steve

leathermang · #4 10-07-2004, 12:30 PM

It sounds to me that you are confusing .....and mixing two different systems...
the Vacuum system for operating the stuff... and the AC system for cooling your car...
They are two different systems.... the vacuum system does not ever "get charged or recharged," etc....

smartin · #5 10-07-2004, 12:40 PM

I was asking about recharging - because I was wondering if the ac system with compressor running (must have freon charge) controls the electric system that controls the change over valves and therefore the vac pods. Maybe there is a cut-out of some kind that does not allow the recirc flap to close (no fresh air) in the event of ac breakdown of malfunction?

Please help

Thanks Steve

D.Blake · #6 10-07-2004, 01:39 PM

Steve,
I again want to stress that my experience was with an 83 W126 and not the 85 W123. With the 83, a non functioning A/C Freon system would have no effect what so ever on the vacuum actuators. The same thing is true on my 86 SDL. The push button control unit controls both but that is their only link. The control unit sends signals to the 6 or 7 (on the 83 it is 6 yours may be 7, my SDL has 7) vacuum valve header block. I first tested each of the actuators by disconnecting the line to the block and then using a mightyvac to test each actuator. I then tested each of the valves by separately running through all of the climate control cycles with a vacuum gage hooked up to each - one at a time. If you do not get vacuum when you think you should them it is either a faulty valve or the control unit. I have yet to hear of a faulty valve so my first assumption was the control unit. It turned out that for the 83 the ACC unit was bad. I also replaced most of the vacuum actuators as one did have a rip and I figured the others soon would. This is not the easiest or most fun job around since it involves electroincs. Anytime you lack a detailed troublshooting manual, it's mostly guess work until you get some experience with it. Good luck!