Date registered: Jan 2008
Vehicle: 1991 560sec. 1969 280SL
Location: New Jersey
Mentioned: 7 Post(s)
Quoted: 238 Post(s)
[QUOTE=GT1;17823186]so here is what i think.
Some sensor not gove the trigger point for this 12V to start at 105C or when AC is running.
I had a 500sel back many years ago on that engine if you disconnected the two wire coolant temperature sensor on the thermostat housing the auxiliary fan would stay on, that’s how you knew the temp. sensor was bad, yours is not coming on from high engine temp. or high ac system pressure. I think you should locate and swap the auxiliary fan relay with one of the others in the fuse box. Some of them are the same.
Check for 12v at the ac pressure switch. Assuming you have power to the pressure sensor, I think if you disconnect the two wires at the red pressure switch that is on the receiver dryer, and bridge them you may find the fan comes on. If it does come on you will know the that switch/sensor is faulty. There is also a resistor in the circuit somewhere under the master cylinder for that fan.
You need member MLB560SEC for a wiring diagram for that circuit.
Last edited by gogi; 06-24-2019 at 01:04 PM.