I bought a two CD Service Manual set for W124 and was hoping it would have a section on blower R&R, and diagnostics but I can't find anything.
1st question is where the blower is (92 300D 2.5T) Do I get at it from the firewall side or under the console?

I have power across the 30 amp fuse and I removed it to make sure it's OK. The connector by the firewall reads 14.3V/0/7.3 (at all three fan settings) at the three terminals and center has continuity to ground. All other fuses and relays test OK.

My aux. fans are also not working. Again, the pre-resistor and relays are all good. I tried to pry the connector off the pressure switch on the evaporator, to bridge it there, but it feels like the plastic will break before it comes off. any tricks? Is the connector for the fan harness in the same area as the pre-resistor and evaporator? Do the two fans work in tandem or does one come on with the A/C and other with high temp?

Sorry for all the questions. I looked through the archives and on the CDs but didn't find answers. Thanks for the help!!

__________________
Reid
Past ('59 220Sb, 2-'59 190's, '92 300D 2.5T)
Current
'04 E320 4Matic Wagon
'00 E320 4Matic Wagon

You get at the blower from outside. Raise the hood to full vertical position, remove the windshield wiper motor and the grill below it.

If you have the same CD as mine, you should have the R&R instructions if you keep hitting the arrows under the Climate Control section. Failing that, there is a very good thread buried in this forum with pictures and very good instructions. Do a search of Blower Motor Replacement or something like that. It is likely that the motor is frozen or has worn brushes.

Good luck,

Both radiator fans run together, either in low speed mode (triggered by the a/c pressure switch) or in high speed mode (triggered by engine temperature). Have you tested the high speed fan mode? Unfortunately I can't give you exact directions; it's one of the sensors on the thermostat housing.

Carefully check all the wiring for the aux. fans, especially around the preresistor. In the early 90s MB redesigned the 124 wiring harness, and the wire feeding the preresistor dropped from 2.5mm to 1.5mm. On my 1993 300E that 1.5mm wire failed several times at the junction with the preresistor. Presumably due to heat from the current load, perhaps in combination with conducted heat from the preresistor. I replaced it with a 2.5mm wire (surprisingly easy to do!) and all has been fine since.

- JimY

I tried bridging the connectors to the two thermal switches on the thermostat housing and the fan didn't go on. I have full voltage on both sides of the pre-resistor, but didn't check amperage, so the wire could still be toast. If I can find the connector, I thought I'd run 12V directly in and see if the fans spin. I wasn't sure what the function of the pre-resistor was, though. (maybe the low speed setting for the A/C)?

__________________
Reid
Past ('59 220Sb, 2-'59 190's, '92 300D 2.5T)
Current
'04 E320 4Matic Wagon
'00 E320 4Matic Wagon

Larry and Jim - Thanks for the information. When I got home, I checked the CDs again and found both the blower R&R information under Climate Control like you said. - also the Aux fan information with the location of the connector. Thanks!!

__________________
Reid
Past ('59 220Sb, 2-'59 190's, '92 300D 2.5T)
Current
'04 E320 4Matic Wagon
'00 E320 4Matic Wagon