W123 Automatic Climate Control Repair -- The Easy Way - PeachParts Mercedes-Benz Forum

biopete · #1 09-27-2006, 01:51 PM

After putting in new AC, I was ready to get my vents to operate as I wanted and fix the heat always on problem. Regarding vents I wanted -- center vents and foot vents open and defrost off or on as needed.

1) Constant Heat aka Monovalve fix -- unplug monovalve, put in a 3/4 " pex barbed ball valve from Lowes (12.00 after tax) in place of auxillary heater pump that is probably broken. This fits right in existing hoses. If you motor works, sell it to someone in the arctic who may actually need it. This 12.00 ball valve eliminates over $300 worth of broken or soon to be broken parts and is dependable.

2) Defrost venst always on: My defrost vacuum pod leaked (and i was not getting vacuum there anyway so rather than repair that flawed system I put a 5/8 ID gates rubber heater hose in defrost channel on dashboard (you can hardly tell its there) to block off air ducts. I need a good way to hold it tightly down yet still be eaily removable. A better solution may be pending (a pulley and wire and handle to manually operate the defrost). Costs about 14.00 for 5 feet of hose ot Oreilley's.

3) Middle vents won't open--
Remove glove box (pull little platic holder tab things with screwdriver, pull light, pull out glove box
reach back and pull rubber boot ducting on middle vents to get at the flap inside
hold open flap, remove metal arm that connects flap to vacuum pod from the flap side (Its the thing that actually opens and closes flap from flap. it just slips off of a pin on the flap. Its easy. Just do it.)
bend metal arm over the flap to permanently hold it open (This is an insiders secret

)
Now you can open and close middle vents manually by twisting vent.

4) Floor vents
I just pushed the flap on drivers side all the way open and it stayed. I may have gotten lucky. That also opened passenger side. I live with these always open.

5) Important -- Disconnect all vacuum lines from pods you no longer use and cap the lines.

Enjoy manual vent and heat control and simpler vacuum system.

brilliantblue · #2 12-13-2006, 01:21 AM

what do you fix when 10 mins into driving the car the main air flap closes and won't reopen in any setting except AC/Cold ? ? ? I need heat! Fan runs but vents close = suck

Wiz3D · #3 12-13-2006, 06:21 PM

Dunno why I didn't think of that ....

W123x3 · #4 12-13-2006, 08:30 PM

Questions on Item #1.
Do you open and close the new valve based on need for heat? Are you removing monovalve or just unplugging electrical connection? Does the thermostat still regulate temperature?

JimmyL · #5 12-13-2006, 08:40 PM

I can see maybe jacking with the vent situation, but the monovalve repair kit is very easy and not expensive....

W123x3 · #6 12-13-2006, 08:45 PM

My impression is that the aux pump is only needed to boost flow at idle. So maybe a straight through connection would suffice in most cases. Does anyone know if the aux pump reduces flow if it is not working?

The manual changes to the flaps sounds promising.

#7 12-13-2006, 09:45 PM

Aside my three Merc's I have had several Buicks and Cadillacs with climate control. I HATE THE @#$^@@%@ things. Just give me a fan switch, temperature knob and vent control!!!!!

Mismost · #8 12-13-2006, 11:48 PM

Item #3...may be easy if you hands the size of a 4 year old little girl! I thought it was very tight back there...but I was try to re-attach the metal strip to the vac pod.

What I wound up doing was using a long screw driver to hold the flap open...then on the right hand side down by the glove box you will see a little white "button" which is actually the flap's pivot point....Super Glue it! Has the same effect...lots of cold air outta the center vents. In fact I think you can do this with out even taking the glove box out (much less removing the whole dang dash!).

mplafleur · #9 12-14-2006, 10:23 AM

You can get a replacement monovalve kit for $20 and replacement rubber diaphrams for the pods for $5 a piece. How much cheaper can you get?

Then the system works great. No hassles.

R Leo · #10 12-14-2006, 10:39 AM

Quote:

Originally Posted by mplafleur

You can get a replacement monovalve kit for $20

Maybe once upon a time they were $20 but they ain't no more:

Quote:

Originally Posted by FastLane

R3023-15174 Mono Valve Repair Kit Bosch IN STOCK $63.65

Diesel Giant · #11 12-14-2006, 06:23 PM

Quote:

Originally Posted by W123x3

My impression is that the aux pump is only needed to boost flow at idle. So maybe a straight through connection would suffice in most cases. Does anyone know if the aux pump reduces flow if it is not working?

The manual changes to the flaps sounds promising.

Yes the pump flows fine if it is not working, but believe me at idle on a cold morning sitting in traffic, that aux pump is really nice! Beats sticking it in neutral and reving the engine to increase the coolant flow.