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Old 11-21-2000, 03:42 PM
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Join Date: Nov 2000
Location: Dushore, PA, USA
Posts: 18
Greetings from a 1st time site user!

I have an '83 300TDT.... runs reasonably well @ 270k miles w/ most maintenance current. Located in mountains 50 miles from nearest foreign auto tech, much less dealership.

Have been plagued w/ the usual plethora of vacuum system leaks (door cells, rubber connections, etc.). Recently I've had trouble w/ engine still running (albeit roughly) after ignition turned off. Shuts off fine manually. Later, developed prob w/ climate control... on econo position,heat only comes out of defroster & dash vents. Found several leaky rubber connectors on vacuum lines in engine compartment & replaced them. Door locks & cruise control work OK, too. Unfortunately, my aftermarket service manual doesn't have a schematic on either the vacuum system or climate control.

My questionS.... 1) are the servos that operate the heater/defroster baffles electrically or vacuum controlled? 2)Basically, am I likely to have more vacuum leaks inside, under dash, or a bad climate control? 3) Is vacuum source only off of manifold or is there a pump, too?

Many thanks in advance for comments.

Bruce Body

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Old 11-21-2000, 09:00 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
Most of it is vacuum. You have an electronic control unit that sends electric signals to a vacuum block that opens and closes the doors in the heater box. I would think that you have a fault in the vacuum system. I would test the VOLUME of vacuum coming from the booster hose. I have seen the line clog up from time to time (hint)>

Donnie Drummonds
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Old 11-22-2000, 08:22 AM
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Join Date: Nov 2000
Location: Dushore, PA, USA
Posts: 18
Thanks, Donnie, for the prompt response. I'll check the line today.

Where is the vacuum control found? Is it actually located inside the heater box & is it accessible?

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Old 12-28-2000, 04:20 PM
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Join Date: Dec 2000
Posts: 17
Heater Air Problems

My '87 300TDT has blower air problems also. On any heating setting, including econo, there is only air coming from defrost vents and dash.

I'm hoping BWBody found something wrong with his vehicle. Any comments would be appreciated.
1987 300TDT 165K MILES
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Old 12-28-2000, 04:58 PM
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Join Date: Dec 2000
Location: Long Island, NY
Posts: 4,026
You most definitely want the factory service manuals for this (or any) car. Benz (and also the partsShop) sell a CD set with all the manuals on it. Also you can find it on ebay fairly often.

If you prefer paper manuals, they too are available from the same sources. There are several: 2 volume chassis manuals, engine manual (specific to your engine), climate control, electrical troubleshooting and transmission service. The tranny book is the only one NOT on the CDs.

There are 10 CDs available for the 107, 114, 115, 123, 124, 126 & 201 chassis (some are pairs). There are 10 CDs available for the 90s (current) models, but they are not detailed service discs, they just have technical training material.

What was the question again? Oh, yeah. You need the vacuum circuit. It's in the books (or the CD).

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Old 12-28-2000, 08:34 PM
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Don't forget the 116! We are a rare and special breed.

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