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Old 02-17-2003, 10:31 PM
The Warden's Avatar
Certified diesel nut
Join Date: Mar 2002
Location: Pacifica (SF Bay Area), CA
Posts: 2,946
Question 123 humid interior when in "EC" mode

Hello! This is actually my first venture into this forum, having mainly hidden down in Diesel Discussion. However, this is a question that, I suppose, would relate to any Benz, and no one down there seemed to have a definite solution, so I figured I'd post it on here.

As my signature says, I have an '85 300D that was originally a Texas car (the car lived there until about 7 months ago). What's happening is that, whenever I have the ACC set on "EC" (standard heater mode; a/c compressor not turning), the interior gets very humid (much more humid than the air surrounding the car). The windows fog up within about 15 seconds to the point where I can't see and everything gets sticky, regardless of where the temp wheel is set or what the outside temperature is. Once I switch back to the regular mode (with the a/c compressor turning), the humidity goes away in very short order. I know that part of the process of air conditioning is the removal of moisture, but my concern is where the moisture's coming from in the first place. There's no sitting water in the car (finally got that fixed ) and the a/c drain hose has been replaced and there didn't appear to be any blockages in the drain leading up to the hose.

It's at a point where I can't use the "EC" mode at all; even if I turn it on without having had the a/c on before, the car gets humid. In addition to replacing the drain hose, I've also put a repair kit in the monovalve (solving a different problem). Any suggestions would be greatly appreciated. Thanks in advance!
2001 VW Jetta TDI, 5 speed, daily driver
1991 Ford F-350, work in progress
1984 Ford F-250 4x4, 6.9l turbo diesel, 5 speed manual
Previous oilburners: 1980 IH Scout, 1984 E-350, 1985 M-B 300D, 1979 M-B 300SD, 1983 M-B 300D
Spark-free since 1999
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Old 02-18-2003, 12:04 AM
The Warden's Avatar
Certified diesel nut
Join Date: Mar 2002
Location: Pacifica (SF Bay Area), CA
Posts: 2,946
I can't readily smell any antifreeze, although I'm open to that possibility...I'm almost afraid to ask, but where exactly is the heater core located, and how do I get to it?
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Old 02-18-2003, 12:37 AM
dmorrison's Avatar
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Join Date: Dec 2002
Location: Colleyville, Texas
Posts: 2,694
Make sure that your AC system is dripping the excess water out the car. If your drain tubes are blocked or partially blocked you may have water in the heater box and its adding it to the car when you run in EC.
How humid is it outside? Your in the Bay area and if its humid this may be normal. Does it occur on a real dry day, if thats posible in the Bay area!!!!!
I would check you AC drain.
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)
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Old 02-18-2003, 12:52 AM
The Warden's Avatar
Certified diesel nut
Join Date: Mar 2002
Location: Pacifica (SF Bay Area), CA
Posts: 2,946
Unless there's a blockage in the molded piece high up, the a/c drain line's fine. I don't know if other cars use this, but the 123 cars had a short styrofoam hose going from a nipple (this is part of the box that the evaporator's in, I presume) to an outlet point that allows the water to exit to the top of the tranny. I replaced that styrofoam hose with the top of a quart oil bottle (I figure it'll last longer ), so I think it's safe to say that that part's okay. There could be a blockage up higher, but I tried poking up the nipple with a toothpick, and it felt free...but, again, I didnt' get all the way up in there.

I haven't had the a/c going for a long time as of late, but last I checked before, it was draining definitely was the day I bought the car, and I had that problem on the drive that night.

BTW, compared to Texas last July, the Bay Area's very dry. The system has been doing this regardless of how humid or dry it's been outside. It even did this in the Mojave Desert last Christmas...and that area's one of the driest places around (real close to Death Valley). So, I don't think it's normal.

Also, if it is the heater core, has anyone had any luck with fixing them? I just went over to Fastlane to check on teh price for a new one, and almost fell out of my chair...
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