M103 aux fan normal operation question...
 

Hi All,

I looked at the schematic of the aux fan and it appears it should not be running 'til the either the A/C pressure switch or the Engine temp sensor triggers their respective relays. Am I correct?

Mine seems to run at LOW speeds when both A and B relays have been removed... please advise...

thanks,

Sounds like your car has been in the hands of someone who didn't/couldn't understand how the system should work and tapped +12V into the line between the low speed/AC relay and the resistor. Does it stop when you disconnect the resistor?

Sixto
95 S420
87 300SDL

resistor...
 

Sixto,

That's one place I have not tried disconnecting... be right back...

thanks,

resistor
 

Sixto et al,

Disconnected the resister and the fan stayed ON... please advise...

I did not unplug the relays this time since it made no diff earlier...

thanks,

The fan stays on at low speed when the resistor is disconnected? Someone must have wired 12V through a resistor between the resistor and fan. As Alice said, curiouser and curiouser.

Try this. Disconnect the resistor from the fan, jump the AC pressure switch and measure voltage upstream and downstream of the resistor. Should be close to battery voltage upstream and somewhat less downstream. That will tell you that the low speed circuit is working.

I don't know how the output of the high speed relay meets up with the output of the low speed relay so I don't know where to recommend a test of the high speed circuit.

Remove the fuse that should power the fan and see if the fan continues without that fuse. If the fan continues, remove the other fuses one by one until you find the fuse that keeps it powered. You might want to skip the radio fuse if you still have the factory radio. I have no idea what to expect if you pull the engine ECU fuse with the engine running. The K-Jet should go to limp mode but you might get a check engine light.

Sixto
95 S420
87 300SDL

thanks...
 

Thanks Sixto... I'm sure the HIGH fan circuit works since I recently replaced a bad engine temp sensor. The bad one kept the fan on HIGH and went to LOW after being unplugged. With the new one, it stay on LOW 'til it gets really hot at which point it kicks into HIGH.

With the LOW circuit, I'm not sure since the A/C is inoperative and upon unplugging, the FAN still runs on LOW.

Where in the aux fan are the connectors... I'll try visually checking to see where the wires run.

thanks,

You might be opening a big can of worms - with no working AC, why is the engine getting hot enough for the fan to come on at high speed? Seems like your clutch fan isn't doing its job.

I don't know where the fan connector is.

Sixto
95 S420
87 300SDL

research
 

Thanks Sixto... Sometimes the fan will be on high after arriving at a destination that's why I know the circuit is working. I will verify the circuit with a few tests though for peace of mind. thanks....

Time to search for some lines....

clutch...
 

Sixto,

I'm just wondering if my problem is electrical. If the fan clutch fails, will it make my fan run?

just wondering...

thanks,

Does your car have an electric clutch? I thought only the 190Es have an electric clutch. If it is a mechanical clutch, do a search on 'Toyota silicone' for an easy fix.

Sixto
95 S420
87 300SDL

correct...
 

You are right... I must be high... sorry...