Air Conditioning Control F78 Rocky


The air conditioning compressor control relay on my 1995 F78 Rocky is oscillating intermittently with a noise like grinding metal on a rough wheel. Enough to drive you to rage!. The relay checks out and operates OK when removed even after an overnight energisation. Coil resistance is 70 ohms. I'm suspecting therefore that its a fault in the temperature measuring/amplifier circuit which drives the relay. Am awaiting a wiring diagram before delving into fault finding that area but would be interested to know whether anyone else out there has experienced this problem.

Check the compressor clutch

Check the compressor clutch first, these are prone to problems on most air con equipped vehicles. If you have access to industrial electric clutches you can usually match one up and replace it with this.