I know this has been asked before but I'm not quite good enough with the search.

Just bought an '84 300d for a SCREAMING deal, been driving it for the past couple of days and find that the dash buttons for heat are mostly cosmetic just now as no amount or combination of pushing the buttons causes the heat to come on or any fan to blow.

My guess is a fuse since its completely unresponsive, I'd say vac if it was blowing cold...

Now, can anyone with experience help me troubleshoot this please? Noob here at the mercy of those who know. I absolutely love this car but I need to be able to defog the windows and heat the cab!

Welcome here! I am fairly new here too. I have an 83 300D, not sure if it is the same as yours. I had the same problem, the fan was not working at all with the button. Check under hood for blown fuse, mine was completely melted. Changed the fuse and voila the fan works again!

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1983 300D 292,000 miles
2002 VW Jetta TDI 153,000 miles

Got Diesel?????

The Climate Control Units (push button thing) have a common problem that leads to the trouble you describe.
To find out, you'll have to remove the unit itself and check for failing solder points on the board, known as cold solders.

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83 SD

84 CD

Hello!

I have recently fixed this very thing on my 83 300DT.

Fuse is the first thing as previously mentioned by bostondiesel. If blown, replace. If it blows again...

Remove the blower motor. Should be 4 phillips head screws holding it into the housing on the passenger side. Check to see if the fan itself turns; if so then put 12V across the leads and see if it begins spinning at high speed. Hold onto the fan tightly now.

If fan motor is bad, then it must be replaced. Possibly expensive unless you can find one at a pick a part. http://www.peachparts.com/ sells em.

You might want to check the hood hinge cubbys for leaf blockage and also check the hood cowl vents for water and crud buildup. Water can pool in the cowl vents and overflow down into the duct work and make it's way to the blower motor shorting it out. Damp carpets on passenger side front are a dead giveaway.

If fan motor is good then... it's on to toomany_MBZ's CCU procedure. Thankfully, I've not had to go that far into it yet. From what I've read, though, it's probably a good idea to do it anyway.

Codifex
1981 240D ChinaBlue (found an engine - hope it's good)
1983 300DTurbo w/sunroof

turned out to be #8 blower motor fuse, fuse wasn't blown it was actually wedged against the plastic of the box, this is because the metal tab that used to hold the fuse in was melted...Some sort of short took place here. But I repositioned the fuse and the heater came right on so I'm going to keep rolling and if it eats a fuse every 6 mos so be it.


On a side note, my other 2 cars are a subaru and jeep and the build quality of this 25 year old car is on another level. It makes the subaru look like absolute garbage, despite being 17 years and 140k miles older... I'm sure this isn't news to you guys but I'm impressed by it. My first car was a volvo and we had 7 or 8 sedans and wagons as I grew up. This car compares very favorably with them. This being my first exposure to mercedes vehicles at $400 I'm completely blown away.

I've used merc diesels in the snowcats I drive at work for years, some of them have VDO guages too. Feels nice and familiar in the 300D...

Thanks for the help everyone!

Quick easy fixes are the best.

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83 SD

84 CD

They're only $0.20 and you'll save plenty of problems and even fix some you don't know you have. Use copper only NOT aluminum.

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James Marriott
2003 Buick Regal
1983 300D (228k, frau Auto)
1996 Suburban K2500 (192k, 6.5 turbo diesel/4WD towmaster 10,000)
www.engineeringworks.biz
1987 300SDL junker 170k
1982 300SD junker, 265k