After suffering through the last several weeks with little heat due to a
nonfunctioning blower, I finally had the time to look into the problem. I've
pulled the blower itself and there doesn't appear to be anything wrong with it. A quick connection to 12 VDC and it spins to life silently and the brushes look
fine. I connected a multimeter to the leads feeding the blower and never got
more than 0.05VDC regardless of the HVAC settings.

I then disconnected the blower controller harness and measured the voltage at that connector - 7.4 VDC at high speed, 1.2 VDC at low speed, and something around 4 volts in the auto position. This leads me to believe that the problem is actually the blower controller (126 820 5310). Since this is a rather pricey item ($400+ even from Rusty or Priceline) I want to be sure of what I'm doing before buying a new one. How can I be sure that the controller is the culprit? Could there still be problems at the HVAC control buttons?

Thanks
Jeff
'87 560SEL

__________________
Jeff

'87 560SEL 267K (177K on motor) Blue/Blue
'98 Buick LeSebre 60K (wife's car)
'56 Imperial Sedan 124K
Past Cars:
'67 Dodge Monaco 130K (Sold)
'87 Chrysler 5th Ave 245K and going strong (sold)
'73 Plymouth Satillite 175K (sold)
'96 Chrysler LHS 80K (totaled)

Hi Jeff
I have the same problem no heat/blower/fan on my 1983 W126 300SD finally found it under the glove box, became a monkey, removed it, and there is nothing wrong with the unit, spins under 12V perfecto, so I re-installed. Now I am trying to remove the wood console dash panel to get at the ACC unit to remove, check and re-flow the solder joints, but cannot remove the wood panel yet. Removed/lifted all the switches, but panel will just not slip down. Any ideas?
This is not a daily driver (yet), and I am retired so it gives me something to do.

__________________
The meek shall inherit the earth, the brave shall get the oceans

Did you checked the 30A strip fuse ? It is located in the engine compartment out side of the fuse box.
I had the similar issue, I did not measure teh voltage so can not help there, but my fan did not work and strip fuse was blown. It will not hurt to try, might save you a lot of money. And if it turns out to be the blower fan regulator a cheeper option is to buty a used one from online source or a from a junk yard.
Keep us posted.

Thanks

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)

Benzmatic, just whereabouts is this "strip fuse"? can you give another clue? Sounds like I should check it before I remove the module. Have already checked and numbered all the other regular fuses but did not know of another.
Any help is appreciated, thanks

__________________
The meek shall inherit the earth, the brave shall get the oceans

I am not sure about your car, but I would imagine it is around the same area. it is behind the firewall next to the big black fuse box. It is a 1 inch X 3 inches black box, had two philips screw on both ends, it opens up by flipping the top withouth unscrewing any thing. Here is the link with pictures of the location, go towards the end of the post.
A/C and Heat

__________________
87 420 SEL
Looking for a nice mid 80's MB diesel.
87 BMW 528e (Sold)
99 TOYOTA 4Runner
1989 Honda Accord (Sold)
1988 Honda Accord (Total)

Jeff
you have checked monovalve and temp relay from engine block?
If your fan is cycling then I doubt the blower control is the issue

Richard
2 screws on underside of center wood just above ashtray.
Must remove ashtray to access.

__________________
Ron
2015 Porsche Cayman - Elizabeth
2011 Porsche Cayman - Bond,James Bond
Sadly MERCEDESLESS - ALways LOOKING !
99 E320 THE Queen Mary - SOLD
62 220b - Dolly - Finally my Finny! Sadly SOLD
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
19 BMW X5 - Heaven on Wheels
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace

Hi Melted Panda
Those two screws are above the radio on my 126. I successfully remove the whole thing today... good job I am retired and have a warm garage to work!!
Removed and cleaned the whole ACC module, all the solder joints look good even under magnifying glass. Will check for voltage before I put her together again.
Dick W

__________________
The meek shall inherit the earth, the brave shall get the oceans