Griffith Heater Control Unit

[lancelin]

Hello, my griffith 500 has just developed a strange cab heater control problem. The footwell motor that controls the amount of hot water entering the heating system is continuously on and rotating the valve in a clockwise direction. This valve should only move to a position related to the position of the cab control knob and shouldn’t be on continuously. I understand this motor is controlled by a little black box in the dash called an HCU. This normally adjusts a control signal to the motor to change its position by comparing the motor position to the control knob position. Has anyone else had this problem? The motor and variable resistors measure correctly and the cables are good. I can only think the HCU is at fault. Where can I get a spare? Or perhaps it’s something else.

[Penelope Stopit]

https://www.pistonheads.com/gassing/topic.asp?t=86...

[lancelin]

Ok, found the problem. It’s the 10K potentiometer that sits on the motor shaft!! It’s not 10K anymore!!! Open circuit! Time to order another.

[Penelope Stopit]

Nice fault finding

[lancelin]

Thanks P, it was your link that prompted me to double check everything. Cheers