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  #1  
Old 01-18-2005, 10:12 AM
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heating woes

Hello All,
I have owned a 300tdt wagen for just over 3 years now. Wonderful car. Is this perhaps the best wagen ever made on the planet? The Heat however has always been a bit strange and recently it's getting to the point where it's starting not to cooperate at all. This is a problem as today in the Boston area where I live,it is around 5 degrees! This problem happens even with the engine warm. The heat works well on low stting. I put in ont auto and it starts to work satisfactory on automatic setting. Then after around five minutes the air is coming out cold. So then I put it on low again and warm air comes out. I try the auto middle setting again and it starts out warm then within 40 seconds becomes cold again. Sometimes the auto setting will prooduce heat lognger. Sometimes using the front deffoger will help. I then go on the highway and go at higher speeds. This aggrevates the heating system now its all pretty much just cold air but keeping on low will start to get the warm air a flowin again. ABout 10 minutes later I exit the highway and drive slower. Now it improves somewhat.
Does anyone know what is wrong here. This is a problem that has gotten progressively worse each year and now is fast becoming a big cold problem!
I have the push button type climate controls. IWhen it's cold and winter, I use only the hot setting on the little finger roll wheel. I only use the econ set button not the AC buttons. Using the AC buttons does not help things. ANY easy solutions here?

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  #2  
Old 01-18-2005, 10:32 AM
meltedpanda's Avatar
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Join Date: Mar 2003
Location: Central Ky
Posts: 6,265
Year of car?
Sounds like monovalve or heater wheel on ACC unit going south, both are fairly easy fixes
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  #3  
Old 01-18-2005, 10:40 AM
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heating woes

Thanks for the reply! The car is 1985. Should I just buy a new monovalve and heater wheel? Do you know of a site of of instructions that show how to replace them?
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  #4  
Old 01-18-2005, 10:53 AM
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Join Date: Jun 2004
Location: West of Ft. Worth. TX
Posts: 4,186
Sounds like the monovalve is hanging up. I would replace it first. Cost about $30 and 15 min. repair.

Near the firewall you will note some smaller heater hoses connected to a valve with 4 screws on top. This is the monovalve. Pull the 4 screws, pop out the old and pop in the new. It is really that easy.

If you do a search of monovalve and photos, there are probably photos of it on this forum somewhere.
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84 300SD 350K+ miles ( Blue Belle )
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  #5  
Old 01-18-2005, 10:55 AM
meltedpanda's Avatar
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I would start with the monovalve. Do a search and you will see it is an easy R/R. basically uplug wire, remove four screws, pull out - repalce. It is a good idea to have car cold and radiator cap off. This will aid in preventing much loss of fluid.
Th other assumption I made is that you have a functioning thermostat. Does your car warm up properly, temp gauge OK?
The ACC unit is an expensive route to take. They can be repaired but I have not had much luck. The monovalve kit is less than 30$ or so.
One other thought that I had was heater core, which is a bad thing, and keep your fingers crossed it is not the issue.
ACC work is often a detective type adventure
Perhaps others will give some thoughts as well
good luck
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Old 01-18-2005, 11:26 AM
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Location: Colleyville, Texas
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A couple of thoughts.
When you go to Auto it gives you a problem. So lets discuss the auto system.
In auto the ACC controller uses the temp sensor at the top center of the dash for its reading of the temp. It does this by drawing air thru the unit via a foam tube just above the glove box liner. This input goes to the ACC controller, which tells the mono valve how much water to allow into the heater core for temperature control.
So lets start with some of the typical items.
1. yes the mono valve can be a culpret. So rebuilt it.
2. The foam tube located behind the glove box, If it has fallen apart then the temp sensor gets an erattic signal. Remove the glove liner, by the screws holding it and look at the inside of the dash at the top of the glove liner. There is a foam tube that should be complete. If it is falling apart then replace it. You can use the foam insulating tubes sold at Home depot for water pipes. Or a hard tube. This just draws air thru it, why it is foam no one here knows.
3. The temp sensor that is at the middle of the dash can break or go bad. You will have to check this, if we get to that point. The service manual covers the check.

http://skinnerbox.steaky.org/Service/Library.html

4. The dial unit which determines the temp you are requesting can be a problem Again the service manual covers this.
5. The ACC control unit is another potential problem,

http://www.peachparts.com/shopforum/showthread.php?t=86657&page=3&highlight=DIY

http://207.210.95.34/~boostd/

Go to resoldering acc control unit

6. Also you have a water pump inline with the hoses going to the monovalve. check to make sure it is operating and not clogged.

Again first check the mono valve and the foam tube, easy, cheap and the usual suspects.

Dave
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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car

Last edited by dmorrison; 01-18-2005 at 11:31 AM.
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  #7  
Old 01-18-2005, 11:41 AM
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heating woes

Thanks everyone! I hope that it is the monovalve. I just bought the kit to repair it. I just hope it's not the heater core!! The car has 160k on it. It was originally in Virginia then spent some of it's life in Florida-not sure how long. The heat does work on the lower setting and deffogger works. Please tell me I won't need to replace my heater core!!! If monovalve does not do it I will replace the heater wheel-I think cost around $140.00.
While I'm here, guess I'll tell more about the car. I bought it in Florida, because I wanted a cancer free car. She was owned by someone who liked aircraft and possibly flies as there is an aircraft owners association sticker on her rear. This is probably good. The car will sometimes shift a bit clunky especially when going about 20 mph and trying to accelorate quickly-it can downshift a bit hard. Usually it seems highway driving at-lets just say Autobahn speeds-makes it shift smooth. I'm told that it's better to have it clunking than slipping. Also maybe a driveshaft coupling is worn. I'm not super knowlegable with this car but I'm learning. I do own a 67 Land Rover and a 1978 Moto Guzzi LM1 so I do have some sense of mechanics if you can call it that-perhaps saying I have serious phsychological problems is better. Anyhow, the rear suspension on My wagon does not work, I'm told it's the pump on the engine. but the car is level and has no suspension leaks so I have not worried. Also I found out it rides fine and handles fine even when I abused it by loading Four inlaws in the back seat and my wife and niece in the passenger seat. The car did not bottom out and ran fine. The driver however needs serious HELP!!!!!!!!!!!
Back to the wagen. The interior is the Blue MTex and the body is the blue as well. Body is super. Intrior is great except sun cracked dash. overall this car is just a joy to drive. I'n my oppinion it really shines in the rain because the steering does not pull when you have to hit a puddle at speed. I've driven many cars and most including newer BMWs will tell you in an unpleasant way that you've just hit a puddle. Not the TDT. It just plows stait ahead. Speaking about steering. I may need a box someday. I've done the idler arm, tie rod ends and bushings-or rather had my mechanic do them. Still a little play at the wheel so I think it's the box.
Any advice is of course welcome.
Thanks for listening and the monovalve advice.

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