Cooling Control Unit for Air Cooled Engine.

Thread Starter

Chris Tyler

Joined Sep 1, 2015
Hi guys,
i am having a little trouble with this cooling control unit i am trying to fix.

In a nutshell it has three temperature sensors, a warning light, and an output to operate the fan solenoid.

What should happen is, when it is powered on and all the sensors are connected the warning light is off and the output to the solenoid goes high to turn it on this stops the fan from running.
When the temp sensors warm up to operating temp then the output goes low allowing the fan to run.
If any of the sensors become disconnected the warning light comes on.
i have it on the bench at the moment, i have resistors to simulate the sensors, if i disconnect any one of them the warning light comes on. So that side of it seems to work ok.

The problem is i am seeing no output to the fan drive solenoid.

In the unit i have, VZ6 is replaced by a resistor. if i short the collector and emitter of VT9 together the output turns on ok.

Any help you can offer would be great, Thanks