Heater / AC Blower oddity - PeachParts Mercedes-Benz Forum

jonschwenke · #1 07-13-2010, 10:09 PM

Here's one for the gurus. My wife's 85 300dt has a blower issue. The "problem" is this. When you push a button on the PBU for the climate control to call for heat or cooling, the blower comes on for a second, cuts off, then maybe 20 seconds later comes on at very low speed, then shortly after increases speeds two more times. This happens regardless of calling for heat or cooling, or which fan speed it is on. Low speed fan does not increase to full blowing though. It is not the blower motor itself. I have swapped a fully working one from my 84 wagon and the problem is the same. I also swapped my PBU in and the problem was the same. Replaced the PBU after checking and resoldering all connections that even looked suspect. Replaced the blower after inspecting brushes, blowing and knocking out crud, and lubing. NO Difference. Also checked and topped off the freon charge just in case it had something to do with the AC pressure switch. I've scanned the forums but have yet to come across this issue. The Climate control seems to work fairly well, but I think the fan should blow harder, immediately and at steady speed, as in my other 80's diesel. Please help. Thanks

nckmsn · #2 07-14-2010, 12:18 AM

Are you hearing the blower actually change speeds or are you assuming that the blower is changing speeds due to the amount of air coming out of the vents?

vstech · #3 07-14-2010, 11:20 AM

it could be a vacuum issue causing the vent doors to open and close on you directing air in places you cannot directly feel.

ds190 · #4 07-14-2010, 03:58 PM

How about the blower regulator? Search threads "blower regulator" or posts under "arthur dalton".

jonschwenke · #5 07-14-2010, 06:04 PM

I had the fan out of it's housing and sitting on the pass. floorboard to witness the abrupt stop, start and speed changes, so not a vacuum issue with vents. I'll check those blower regulator posts. Thanks. Any other ideas?

TSH24 · #6 08-30-2010, 09:41 PM

Just curious if you figured out your blower problem? Mine was acting somewhat erratic similar to yours and has now stopped all together... It does seem to blow on a very, very low setting.

jonschwenke · #7 03-09-2011, 03:32 PM

Quote:

Originally Posted by TSH24

Just curious if you figured out your blower problem? Mine was acting somewhat erratic similar to yours and has now stopped all together... It does seem to blow on a very, very low setting.

I did figure it out. The in dash CCU had barely visible hairline cracks in two solder joints. I resoldered and all is good! SO when inspecting that puppy, use extreme scrutiny THE FIRST TIME.. Do as I say...not as I do!