The reason for jumping the a/c high pressure switch is this is the first step
to diagnosis on this 124.032 system.
This quickly checks the integrity of the electical circuit for low [a/c ] fan.
If the fan does not come on, then you go to relays,fuses, dropping resistor,
This test takes all of 20 secs and will tell if the problem is theelectrical
circuit or freon pressure related.
If the fan comes on w/jumper , then you have a good relay. fuse, resistor, fan
circuit. In which case , the problem is that the high side a/c pressures are
not getting to cut-in specs [ 20 bar] to turn the circuit ON.. This can be a
bad sw., but the most liely culprit is you have a shortage of freon charge-
thus not enough high pressure to trip the fan circuit.
Remember this when diagnosing fan circuits on 124.032:
There are TWO completely different circuits for the 2 speed aux fan.
They each have their own fuse/relay/ and sensor circuits . They just share the
SAME fan motor.
The high fan is tripped by the 2 wire thermistor sensor at the thermo housing
and it is set to trip at 105C , collant temp. This is the blue relay.
The a/c low fan circuit is tripped by the high pressure of the a/c compressor
system and has NOTHING to do with the high speed coolant temp sensor circuit.
It consists of a relay,fuse, high pressure sw. and a dropping resistor [
behind driver headlamp].
SO.. no low fan, you are in the a/c pressure activated circuit....
No high fan, you are in the Engine coolant temp senor circuit.
Also, Benz had a TSB fuse change on this chassis allowing up-gradeing the 15
amp fuse on the coolant temp relay to 25A....