I could use some help on this one. Just purchased a 77' 300D, the a/c doesn't work, but not worried about that yet. The climate controll only puts out heat. I can select hi and low auto, bi level and defrost just fine. It just won't blow cool outside air.
I first thought the Mono Valve, but turns out the 77' system doesn't have one. Can't find any info about non-mono valve systems. I am wondering if it is a problem with a "hot/cold air mix valve" or something else. I don't know how the system works.
Any hints on trouble shooting a non-mono valve system would be great!

Believe that cars in your era up thru 80 or 81 had the so called "dreaded servo". This is a plastic box sitting above or slightly inboard of fender well on passengers side. This item has a lot of vacuum lines and heater hose entering / exiting. Do a search for A/C servo or possibly ACC servo, should find all kinds of info and tips.

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1961 190Db retired
1968 220D/8 325,000
1983 300D 164,150

Thanks for the tip, I found that the ACC Servo is more trouble than it is worth. I am going to install a manual by-pass kit that controlls the water flow to the heater core. Not as elegant as the auto system, but much more effective and dependable! Dependable is what I am looking for.

A tech put a very large ball bearing in the output hose for the servo to cut off the coolant supply. Obviously the ball bearing is large enough that it doesn't move around.

I put the ball bearing in in the summer and take is out in the winter.

JCD

jcd,

How do you regulate the temperature with the ball bearing in?

Adam,

I think you have the right idea, just control it manually and be done with it.

Good luck,

I have the same question with a new purchase ('84 300DT). Hot air out the vents.

I assume my issue and fix is different. Any quick thoughts?

Thanks

Don

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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
'82 240D 229k (Matt's - Converted-300DT w/ 4 speed

diesel don,

I expect the problem on yours is the monovalve. THe '77 doesn't have the monovalve while yours does.

Good luck,

JCD

I am sure the ball bearing does the trick, but it is a all or nothing solution. Check out this web sight:[URL=http://www.mercedessourse.com]
and take a look at "do-it-your self Kits", you will find a "123 early climate control conversion kit". All you guys with ball bearings may like to switch to this so you can have greater control over the heat system. Just a thought. Take care.

How regulate heat.

Ball bearing in............... AC mode.

Ball bearing out............. heat mode

The ACC dial does "regulate" heat within either mode, but AC to heat is either on or off.

www.**************.com's kit looks pretty cool and Kent is a good guy that is reliable and provides good instructions. I've bought a couple of parts from him in the past and he is a good guy.

I made up my own manual cutoff valve, (actually the maintenance guys at work did it for me) but I'm only going to put it in when my current servo springs a leak.

JCD

85 300d. Ac works when the temp wheel is all the way to min. Once rolled off the min temp of the wheel, the temp in the car goes very hot and does not mix with cool outside air at all. Monovalve??? I either have very hot air comming in or very cold , no medium.

Don't I feel silly. While working on replacing my front dash speakers, I found the temp sensor mounted in the right speaker grill, I also found it didn't have a wire attached to it. After some elbow deep dashboard digging I located the wire, hooked it up, and guess what, the dreaded ACC system works perfect! Just need to charge up the A/C now.

I did already order the manual bypass valve, but I think I will hold onto it. I know it is only a matter of time before the Servo Valve dies. It all works out in the end!

If you wanna sell that kit, let me know... my servo is leaking, and I'm not gonna shell out for a new 'metal' (oooh metal, why didn't the MB engineers think of that?) unit. Not now, anyway.

Cool deal on the simple fix, btw!

Ash

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Ash Peltier - tools, truck, tales
---------510-331-4118-----------
1982 240D - (272,000)
1998 Honda VTR1000F(RT) Superhawk Freeway (58,000) "Madrid"
1996 Toyota T100 4x4 (84,000) "Mary Kay"

holee... that kit's wicked expensive for what it is, no? Seems like OSH would have a valve that'd work, and I can deal with switching from under the hood. What on earth makes that kit cost $90?

__________________
Ash Peltier - tools, truck, tales
---------510-331-4118-----------
1982 240D - (272,000)
1998 Honda VTR1000F(RT) Superhawk Freeway (58,000) "Madrid"
1996 Toyota T100 4x4 (84,000) "Mary Kay"

Yea, fair enough... dude's gotta make a living, I guess, can't fault him for that. However, I'm genetically prohibited from buying stuff that's more expensive than it's worth plus, oh, I dunno, like 100%... and that's only if it's really inconvienient for me to do without it. Who knows, though... by the time I'm done buying parts and screwing with it, it might be worth it to buy the kit... hey... maybe a group purchase..

Ash

__________________
Ash Peltier - tools, truck, tales
---------510-331-4118-----------
1982 240D - (272,000)
1998 Honda VTR1000F(RT) Superhawk Freeway (58,000) "Madrid"
1996 Toyota T100 4x4 (84,000) "Mary Kay"