I was working in my 1976 300D w115 the other night, decided to run some heat. No heat. Sympoms as follows:

AC will turn on blower
Blows only cold air
No blower with AC off
No air to floor vents

AC Vacuum switch tested
Vacuum actuators function properly under dash
Change over switch functional (metered out)
Flused heater core, all lines hot.
Blower switch has 3 speeds W/AC on, inop w/AC off
checked fuses and Voltage from ignition switch
checked grounds
performed search for similar problems

The electrical diagram shows two blower motors, one for AC and one for heat, I think? Are there actually a second set of blowers somewhere in the big black box? Or do they refer to them by thier function at the time. I would appreciate any help before I tear into this mess.

Yes there are 2 blower motors on this car!! The one for the heater is a total pain in the re@*.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator

Yep. It's got a normal fan type for heat and a squirrel cage for the AC. You have to remove the dashboard to replace the blower motor. My '75 was squealing and squawking like crazy. And it is a pain in the a$$.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

I was a fraid of that but the way my luck has been going lately I should have expected it. Just got done putting the dash etc back in after paint & carpet etc. Thanks for the help. At least my seats are still out.

As an aside what are the differences between a 75 & 76?

MAKE A TEST LEAD WITH A 15 AMP FUSE INLINE.
DISCONNECT THE PLUG AT THE CHANGE OVER SWITCH AND FIND THE 1.5MM WIRE (RED W/YELLOW TRACER.)PLUG YOUR TEST LEAD INTO THAT WIRE AND CONNECT THE OTHER END TO BATTERY POS.
WITH THE BLOWER SWITCH ON HIGH (POS. 3)BLOWER SHOULD WORK IF MOTOR IS GOOD AND SWITCH IS GOOD.
IF BLOWER IS STILL IN/OP GROUND THE 1.5MM. GREEN W/BLACK WIRE AT A/C MOTOR.THIS WILL BY-PASS THE SWITCH.
IF IT STILL WON'T BLOW THEN YOU CAN START CUSSING!
MF

Pulled motor. Metal clip holding one of the brushes is gone and brush mangled. Thanks for the help.

On the brighter side I now have an opportunity to clean the box and coils and get that 25 yr old smell out of the system. There were some interesting things down there. I found a cigarette but with no filter, smelled kind of funny. A blue crayon, a bank pen, coins, gumwrappers (doublemint and juicey fruit), bobby pin, screws and lots of fuzz.

Not sure what any difference may be between the 75 and 76. I miss it though.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)