1987 300D Auxiliary Fan Problem - PeachParts Mercedes-Benz Forum

iamtheosprey · #1 06-07-2014, 07:14 PM

I noticed that my fan wasn't working while A/C was on.

I checked the fuse and it was blown.

Once I got home I put in a new fuse, started the car and turned on the A/C but the fan didn't come on.

At what point is the Aux fan supposed to come on?

I thought it was as soon as you turned on the A/C.

Does it have to get to a certain temp first?

vstech · #2 06-07-2014, 08:02 PM

It has to reach around 100C first I think

Caseyc · #3 06-07-2014, 08:12 PM

My MB mech bridged mine to operate anytime the AC is on. It was running to warm for comfort by the time it hit its thermostat. All he used was a 2" wire with a male end on each side. Nothing was cut or altered in the harness. Easily reversible. He said he likes to do this when during the warmer months.

vstech · #4 06-07-2014, 08:44 PM

Are you sure this does not bring the fan on whenever the KEY is on?

Mxfrank · #5 06-07-2014, 09:43 PM

The fan is activated by a pressure switch located in the receiver drier. It's triggered when dischage (high side) pressure exceeds 20 bar (300 psi0. This isn't a normal condition, and would probably only be reached on a very hot day with no forward motion. When people say their fan comes on as soon as the a/c is on, I assume they've overcharged their system (unless the switch is bridged).

That said, there are a few more things involved that you should check. Specifically, the low speed resistor and the relay.

sixto · #6 06-07-2014, 09:55 PM

IIRC the high pressure switch triggers the fan at low speed. Check the resistor behind the left headlight (best to pull the headlight). I'll bet the resistor coil is burned and/or rusted open. But first, check the fan at full speed by bridging the paired sockets on the connector that goes on the 3-pin temp switch on the upper radiator hose fitting.

Sixto
MB-less

iamtheosprey · #7 06-07-2014, 11:26 PM

Well, after noticing that the fuse was blown I tried to spin it by hand it and didn't want to move at first.

Eventually, I managed to spin it and something sounded like it crunched or fell out of it and it started to spin but not really freely.

Then, I unplugged it and connected the plug to a power source and the fan spun but made a few squealing noises.

I have another fan that is the same size but actually is on a different frame.

I bought it for my '93 300D off ebay when I had it but that car had dual aux fans so I obviously couldn't use it.

I kept it about four years and what do you know...now I have a use for it.

I measured it and it has the same diameter as the fan that's on the car now and when I powered it up it seemed to spin faster.

When I spin it by hand it spins much more freely than the one on the car now but still not really free.

I guess for the time being I will take it off the frame it's on now and see if it will mount to the frame on the car.

All it has to do is stop raining...

vitop · #8 06-08-2014, 12:17 AM

I think you have onr large fan on that car? Mine uses two smaller ones. Just thought I'd give my experience. I just had to buy a new fan. I normally buy Mercedes for everything, but they just wanted too much for this fan (IMO). I bought the ACM brand and did not like the looks of it and did not even install it.

I switched it for the Meyle version (I normally am not high on Meyle) and it looks like the original fan. It costs a bit more, but IMO is better made.

Mxfrank · #9 06-08-2014, 09:26 AM

The old fans can sometimes be salvaged. Crunching noise could be a collection of leaves and bugs behind the fan.

the trick to disassembling the fan is that the blade nut is left handed. Clean it out carefully, and put a drop of oil in each bushing. As long as the coils haven't burned, that should do it. Worth a try before you invest in a replacement.

iamtheosprey · #10 06-08-2014, 12:19 PM

Quote:

Originally Posted by Mxfrank

The old fans can sometimes be salvaged. Crunching noise could be a collection of leaves and bugs behind the fan.

the trick to disassembling the fan is that the blade nut is left handed. Clean it out carefully, and put a drop of oil in each bushing. As long as the coils haven't burned, that should do it. Worth a try before you invest in a replacement.

Thanks for the info.

I'm going to take it out today and do that.

I also have another salvage motor/blade that I will compare it to and reinstall the best of the two.