Infuriating 124 Defrost Problem - PeachParts Mercedes-Benz Forum

jbhebert · #1 12-23-2004, 10:54 PM

I recently picked up a '95 E300D, which I am enjoying tremendously. However, I am starting to dread damp and rainy days in this car because of its absolutely abismal windshield defrost. I have to assume that MB didn't intentially design a system this inadequate, so I am going to assume that there is a problem.

(For ease of identification, I'm going to lable the buttons on the climate control A-E, left to right. Defrost is A and Off is E).

In cold, dry weather it takes forever for the windshield to clear, but it does eventually, even left on D. However, when it is rainy or humid, anything but A usually makes the windshield worse. I have a 75 mile, 1.5 hour commute, so I have a lot of time to mess with the system.

Today, it was rainy and humid, around 55 degrees (F).

On C or D, there is a slight amount of air felt coming from the defrost ducts. On B, there is more air coming from the defrost ducts. On A, there is a ton of air coming from the ducts. The system seems to route the air correctly, so I do not believe it is a vacuum pod issue.

On A, B, and C, I can see and hear the A/C compressor engaging, so I do not think it is an A/C issue.

On A, the system DEFINATELY cranks at full heat, as it's supposed to. This is how I drove home today, with the rear windows down so I wouldn't pass out from heat stroke.

When attempting to defrost, I never use the recycle button.

A does a reasonable job clearing the window, but even then there is a strip of fog along the top of the windshield. B, C, and D all *increase* the amount of fog on the window. I'm better off switching between E (off) and A (full blast) for the duration of the trip, which isn't really ideal. I am not getting any coolant smell or an oily film on the windshield, so I don't think the heater core is leaking.

Based on this info, I have to guess that I'm getting moisture in the heater box that is getting blown onto the windshield. I assume there are some drains that I can check, but I'm not sure where to look.

Any suggestions on the problem, or where to look for the drains, would be most appreciated. I hate the fact that my '92 GMC pickup (actually, EVERY vehicle I've ever owned) has better defrost on low fan than my MB has on max.

Thanks in advance!