1980 300td HVAC bypass question - PeachParts Mercedes-Benz Forum

turbozeke418 · #1 09-09-2013, 01:35 AM

I have a 1980 300TD and have been driving it for 3 years with no working HVAC. The only setting that works is the defogger setting on high and cranks out good heat (i could care less about AC for the summer). I don't want to troubleshoot the system and there's parts missing to the servo unit under the hood. Is there a way I can access where the vents close in the duct work and make the defogger setting blow out the upper and lower vents also? Basically looking where to access that area and just take out whatever closes off the vents from the defogger.

cooljjay · #2 09-09-2013, 02:54 AM

There is no way to do this....unless you buy the unwired kit or fix the HVAC system.....there's a computer that controls the servo, and the servo controls the vent operation.....what is missing under the hood?

This will tell you everything you want to know about the evil servo system..

http://www.imperialclub.com/Repair/Lit/Master/281/cover.htm

If you want to get it going on the cheap, this guy has a working amp and servo....it doesn't look like its the aluminum version, so you would still need to watch for leaks......you would also need to unplug, unfreeze and fuse your aux water pump as this usually kills your amp.....then there is also a foam sensor tube behind the glove box that rots to dust that needs replacing....

http://www.benzworld.org/forums/sale-wanted-trade-giveaway/1734553-f-s-78-300d-n-engine.html

There is also a chance, that all you need to get yours going again is a new amp, sensor tube and fix the aux water pump...

turbozeke418 · #3 09-09-2013, 05:29 AM

OK thanks for the info. For the amount of time I drive it (not much in the winter since I run both my 123 and 126 on WVO) I'll just use the heat from the defogger. Thanks for the info anyway.

cooljjay · #4 09-09-2013, 03:25 PM

Alright.....just remember if that old plastic servo cracks, the effects is overheating and typical ruining the engine.....keep an eye on it!

Mölyapina · #5 09-09-2013, 04:27 PM

Quote:

Originally Posted by cooljjay

Alright.....just remember if that old plastic servo cracks, the effects is overheating and typical ruining the engine.....keep an eye on it!

The engine overheats if the servo cracks? Is that because coolant leaks out of the servo?

Phillytwotank · #6 09-09-2013, 04:47 PM

Quote:

Originally Posted by cooljjay

There is no way to do this....unless you buy the unwired kit or fix the HVAC system........

I think thats jumping to conclusion there. I'm sure it can be done.

Totaly hacked up and custom redisigned? Yes!

But definitely doable IMO

cooljjay · #7 09-09-2013, 06:25 PM

Quote:

Originally Posted by Jooseppi Luna

The engine overheats if the servo cracks? Is that because coolant leaks out of the servo?

Exactly....it cracks, coolant leaks out and if you don't watch your temp gauge....you will soon see steam...

Quote:

Originally Posted by Phillytwotank

I think thats jumping to conclusion there. I'm sure it can be done.

Totaly hacked up and custom redisigned? Yes!

But definitely doable IMO

Yes for the average folk, it's not jumping to conclusions....you just can't unplug this, plug it on there....add this and wa la ability to control the vents manual...

Now to us tinkers, who don't want to spent 700-1500$ to get it running right....we could figure out a cool redesigned idea....I often want to find the unwired kit, and see what they did and construct a cheaper solution say for a few hundred bucks....and offer it up...

I was lucky and found a new aluminum servo on eBay for 50$ and a new amp at pick n pull.....then I bought a good aux pump...piece of foam insulation and for maybe 80$.....my servo system was fully functional....minus the ac...

Phillytwotank · #8 09-09-2013, 09:26 PM

I took it as... The OP is wanting to have a a system that is permainantly fixed into one position not to have any control over the system other than simply on max fresh air or off. i say it can be done fairly easily.

"fairly easily" is a relative viewpoint I guess. All depends on time, ability and what is an acceptable level of hack up.

- Disable all vacuum pods and physically "jam" them into the desired position
- Plug all the vac lines to avoid leaks
- Bypass hot water to the heater core (sounds like this might already be done)
- Done

Push the defrost button and there'll be fresh air blowing from all vents on max blower.

The UT kit is simple also. Basically two three way vacuum switches,micro processor, vacuum controlled hot water valve,wiring harness and a few vacuum conection pieces to get it all hooked into the original system. I don't know what they're selling for these days but i feel like it's been worth the $550 that I paid. Yeah no fresh air control build in but it's not too bad to have Always fresh air and it's easy to add a very small ball valve to gain control of the fresh air function.

ROLLGUY · #9 09-10-2013, 12:34 AM

The other option is to get a complete manual system from a 240. Yes it is a lot of work, but this solves ALL the problems with the CC system.

cooljjay · #10 09-10-2013, 03:07 AM

Quote:

Originally Posted by ROLLGUY

The other option is to get a complete manual system from a 240. Yes it is a lot of work, but this solves ALL the problems with the CC system.

+1

I am seriously contemplating this....but I am not sure if my car is worthy of such a swap.....but every time I do a coolant flush, I look at all the heater hoses....rubber and metal, plus all the vacuum lines....and electrical....I am like its just to much crap....then I look at all the ac stuff....I am like, if I just remove everything and go manual with out ac.....I would lose like 100lbs of extra weight....but on the other side, I find the acc system...so interesting, I love the flaps...all the buttons, the noises....just so cool, in a geeky mechanical way

cfh · #11 09-10-2013, 09:05 AM

Going manual is a great solution. Did this on my '80 CD several years ago to finally be rid of the curse of the evil servo. Just swapped over the entire hvac cabinet, controls and wiring from a 240d parts car. Wasn't so bad - looks a lot more difficult than it really is. The results were worth the effort. With the dash out and the cabinet removed you have great access for adding soundproofing, too. Recently I complimented the upgrade with Rollguy's Sanden package; couldn't be more pleased (a/c is a major priority around here!). Be sure to check out the heater coil before you put everything back together. -- Ch

ROLLGUY · #12 09-10-2013, 12:17 PM

Quote:

Originally Posted by ROLLGUY

The other option is to get a complete manual system from a 240. Yes it is a lot of work, but this solves ALL the problems with the CC system.

After posting, I thought the suggestion would meet a lot of resistance. It does seem like a lot of work, but it is worth the effort and expense. This job is not for the novice mechanic. However, there is much support and detailed threads here should someone decide to take on a project like this. After using the manual system, you tend to get spoiled.

Quote:

Originally Posted by cooljjay

+1

I am seriously contemplating this....but I am not sure if my car is worthy of such a swap.....but every time I do a coolant flush, I look at all the heater hoses....rubber and metal, plus all the vacuum lines....and electrical....I am like its just to much crap....then I look at all the ac stuff....I am like, if I just remove everything and go manual with out ac.....I would lose like 100lbs of extra weight....but on the other side, I find the acc system...so interesting, I love the flaps...all the buttons, the noises....just so cool, in a geeky mechanical way

That is all true only if it all works properly! The key word is: properly. It seems that the weak link in all the climate control components, are those that MB purchased from the U.S. The "evil servo" system (or the rights to use such designs) was purchased from Chrysler, and the Delco R4 from GM. These pieces of equipment are a constant source of irritation for us 'Benz owners, and much has been done in the aftermarket to lessen that irritation. Us Americans want comfort (and are lazy), and that is why the early CC systems were more "automatic" in cars made for the American market. The cars made for the rest of the world had manual everything- windows, transmission, climate control, sliding roof etc. Sometimes manual is much better...Rich

Whiskeydan · #13 09-10-2013, 07:04 PM

$20 worth of parts will 'manualize' it and get you 20lbs lighter.
Toss the evil servo in the trash and use switches to turn on vacuum valves for vent pods, a switch to turn the AC compressor clutch on and a switch for the coolant valve for heat.

I've done this on a few cars that PO had hacked up beyond repair.

If you want to do it really cheap just let the vacuum lines hang down and connect the vacuum source to the desired pod to steer the air... dash vents in summer and floor in winter. Default is defrost. Manual water valve under the hood for coolant flow for winter mode.

Use a DPDT with center off switch for blower "Low" speed thru resistor, center "OFF" and up position for "Hi".

kerry · #14 09-10-2013, 07:17 PM

Just prop open the footwell vents. Not that hard to do.

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