W123 aux fan not coming on - PeachParts Mercedes-Benz Forum

VW1300 · #1 07-01-2011, 12:01 PM

Yet another thread on aux fans. I searched previous posts, but didn't see my problem, but then again there are 351 results for "aux fan".

With the engine at 90C and the A/C blowing cold, the aux fan never kicks on. I checked the connector underneath and found 0.0 V. Other threads talk about checking a relay and switch for this - where would these be on a 123? And what do I check next?

thanks,

leathermang · #2 07-01-2011, 01:09 PM

There may be one on the engine..perhaps on the thermostat housing ?
and one on the rec-drier ....

tangofox007 · #3 07-01-2011, 01:14 PM

Quote:

Originally Posted by VW1300

With the engine at 90C and the A/C blowing cold, the aux fan never kicks on. I checked the connector underneath and found 0.0 V.

Engine temp is not a factor. Refrigerant temp is. Low refrigerant levels can prevent aux fan actuation.

Quote:

Originally Posted by VW1300

Other threads talk about checking a relay and switch for this - where would these be on a 123?

Switch is on the receiver/drier; relay is on the top of the left-side, front wheel well, usually under a black plastic cover.

leathermang · #4 07-01-2011, 02:04 PM

Your car may have more than one criteria to turn on the aux fan...
the engine temperature..
and the need of the AC ...
I can not imagine a reason for the refrigerant being low to cause the aux fan to not come on if the engine needs it for cooling purposes... (?) ...

tangofox007 · #5 07-01-2011, 02:37 PM

Quote:

Originally Posted by leathermang

I can not imagine a reason for the refrigerant being low to cause the aux fan to not come on if the engine needs it for cooling purposes... (?) ...

An '85 could be different, but on earlier year models the only factor involved in the operation of the aux fan is refrigerant temp. (Yes, I am 100% sure of that.)

Apparently, the designers considered the aux fan to be a refrigeration component only. Like it or not. (That said, there are other models wired to operate the fan on the basis of coolant temp and refrigerant temp.)

leathermang · #6 07-01-2011, 02:38 PM

I don't like it.

tangofox007 · #7 07-01-2011, 02:50 PM

Quote:

Originally Posted by leathermang

I don't like it.

My '82 300D will maintain a coolant temp of around 85* in any ambient temp as long as the a/c is not on. If I didn't have a/c, I would have no need for an aux fan.

leathermang · #8 07-01-2011, 02:59 PM

But all cars are not in as good a shape as yours...
I have trouble believing that people who had been making cars for nearly 100 years would structurally limit the aux fans to the AC... even when the engine might be needing cooling for other reasons....

VW1300 · #9 07-01-2011, 03:03 PM

A/C was charged up about a month ago so I wouldn't think pressure should be too low. Will check the relay on the front fender, thanks for the info. Probably won't get around to it until some weekend evening, right now it's 97 degrees in the shade here in Houston and I don't feel like going out there. I will report back on what I find.

thanks,

Yak · #10 07-01-2011, 04:50 PM

With the ignition on, you can jumper the wires at the switch on the R/D for a quick check. There's a pic in post #13, here: W123 aux fan not coming on

The switch is off of fuse 14, I think the fan motor is off of C. If either is bad you won't get power to the fan. As mentioned, the relay could also be faulty.

my123ca · #11 07-01-2011, 07:18 PM

I would check if the fan is in fact working or not. Follow the wire of the fan, you will see a connector. Separate the connector and apply power to the terminals. My problem has always been with Fuse c.