I have a 1989 190E 2.6 My Aux Fans don't come on in the low speed mode. Naturally my A/C compressor will kick off as the high side pressure gets too high. The fans come on in the high speed mode so I know the fans are OK. I bridged the high pressure switch on the receiver dryer and they still don't come on. So the pressure switch isn't the problem. I checked the fuses in the fuse box and they are all OK. The ceramic fuse has continuity. My meter shows about 4000 ohms. I tried jumping the ceramic resistor anyway and still no fans. Looking at the wiring diagram I see there is a relay for the low speed fan. Does anyone know where this is physically located? Could there be another problem outside of a broken wire?

Thanks
Pete

The box behind the fuse box [ 6 screws] contains the relay with a 15A fuse on top.
Change that fuse.

How do you get to this box. I can't even get the fuse box cover out. Do I have to remove some of the plastic trim around the windshield?

Pete

They should be in each corner of the fuse box.. open the hood to full up position..it is part of the rear section of the fuse box...do you have the fuse box cover off??

All that is in the fuse box is 3 rows of fuses. Behind that are two silver relays. Behind that there is a big black relay that is a little wider than the two silver relays put together. There are no fuses on top of any of the relays. This is a 190E 2.6. I can't get the fuse box cover off, but I can tilt it open and get my hand in there. I already swapped the two silver relays, they were identical. I pulled the big black one out and opened it up. There are 3 relay switches inside, and they all look OK. Any ideas

Pete

I don't have that schematic..
If you have high fan it has to be feed to the low relay, which has to be fused.. spin the fuses.
Can you send that schematic jpg??

I only have a diagram for a 1987 model. My car is an 89. For the 87 it shows an aux fan pre-resistor relay. I don't know how to capture the picture to send it. Unfortunately it doesn't show the actual location of this relay.

Pete

OK

I have a schematic for a '89 2.6 in the 124 chassis,so it might be close
According to this , it can not be fuses cuz both relays use common feed fuse for both fan load and relay primary coil.
So, do this
key ON
jumper pressure sw .. [ be careful here that you are jumper correct sw , there are 2. The one you want has brn. pigtail wires .. don't jumper sw, but rather the wires leading back to firewall] you can just lift sleeve for wire connectors and jumper while leaving sw in circuit. That should get low fan .
If fan does not come on, but you can hear the relay clicking, than we have relay circuit.
Now , try this
No key needed for this test
run jumper wire from bat + to the dropping resistor .Touch the side with 2 wires on it .. this will give high fan.. then go to side with one wire on it .. same deal, but you should have low fan .. if not , you have bad resistor or connection there
I will see where the relay is located for the 124 2.6 and get back to you
try the above

I put the car away for the night, but I did do some of this earlier. When I jump the switch the fan does not come on. I also don't remember hearing a relay click. I'll try putting 12 volts to the resistor tomorrow. I did check the resistor for continuity and it was OK. Also as I previously stated the fans do come on high if I pull the wire from the two prong sensor on the cylinder head, so I know the fans are OK

Pete

OK

This location shows slot B behind fuse box to be low fan relay [K-10, pre-resistor relay] location.
I think you can not get cover off fuse box cuz it lifts from the front and then the hinge can be pulled foward from the slots to lift it entirely off. But that is 124 , so not really sure ..take a look anyway


My concern is resistor omhs seem way high to me, so the direct bat jump with the resistor in series will tell the tale..

OK I couldn't resist so I pulled the car back in. When I put the hot 12V on one side I got the high speed fan. When I tries the other side I got nothing. When I check for continuity the resistor isn't "open", so what's going on. I took the wires off the resistor and the problem is now clear. The side with the 2 wires wasn't properly installed at some time in the past. It was a little loose, and the contact area on the resistor is totally rusted. It's impossible to clean it up so I'll drop by the dealer tomorrow and get a new one. The problem should be solved. Thanks for your help.

Pete

Yeah. that is a common find
The main reason I sent you down there for that particular test is cuz a dropping resistor runs between .3 and .4 ohm.. not even 1..
That give the resistor approx a 55 watt draw to accomplish the speed drop.. also why they get so hot and are made of ceramic..
See ya