89 300 SE
Full a/c charge. A/c works great. I had no aux fan with a/c on and a jumper at the dryer switch.
Installed new fan resistor..... no fan without jumpering. But it comes on now with a jumper, at what appears at high speed, and does not shut off when you shut off the a/c.
1. Is there a relay to check, and where is it located?
2. Can I leave the switch jumpered all the time, summer months, or will I burn out the wires?

It's possible that the switch is working correctly. The fan will only operate when the temperature switch closes. This happens only when the vehicle is sitting with no movement in a rather warm ambient.

I rarely hear the fan operate with any of these. I've seen the SD operate it's fan when sitting at idle for an extended period.

You could permanently wire the fan to run all the time........but why??

As I understand there is 2 triggers. One for high temp, the other for a/c operation. The temp trigger works fine... hits a certain temp.... kicks on.

Its the a/c trigger that has a sensor on the high pressure side of the a/c system. This is the one giving me problems. Its should come on and off with the a/c button...in dash ... as I believe.
If I jumper the a/c switch, it comes on high speed. Is there a relay in the fuse box to check? ... I just put in a new resistor under master cyl.

AFAIK, that sensor is a temperature sensor as well. As mentioned, it won't come on unless the a/c system temp. gets too hot. This occurs when the system has low air velocity across the condenser.

I believe the temp sensor is on the head and seperate.
Do you happen to know where the aux fan relay is located in a w126?

My fans failed to turn on about a week ago with the A/C. They did turn on with the temperataure though. The only thing that I did to save me money and time was run a wire from the A/C's temperature switch to the fans relay. I ran it to the ground wire of the relay, now when I turn my A/C on about a minute or so later the fans kick in at high speed and shut down when the A/C cools again and so forth. And they also turn on when the engine is getting hot too. The relay is the first on or the second one in back of the fuse box in the drivers side of the engine. There's alot of relays so first or second to the left of the box towards the passenger side.
92" 300E

Ken,
Brian is correct. The switch on the R/D for the aux. fan is a temperature sensor/switch. Turns the fan on when the refrigerant temperature reaches
52º (red code switch). Earlier switches were higher (62º, I believe).

The coolant temp sensor operates the high speed of the fan; the R/D refrigerant switch operates low speed, as far as I recall.. My car has a fan relay. Yours may be part of Klima or MAS. I try to check the electrical manual.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)

Thanks for helping me figure this out. Can I change the temp switch without losing the 134?

IIRC, you can change the temp. switch.........but.........I'd prefer if someone confirms this.

Why do you believe the switch is bad?

It won't close until the refrigerant temp. setting it exceeded........a rare condition........unless the vehicle is not moving.

No. On the old style R/D you could, but not on yours. Too new

Check the two ice cube relays closest to the firewall, driver's side, in the fuse/relay box. They are the low and high speed aux. fan relays on other gas 126's. I just don't know the 103 well enough.

__________________
The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)