All of a sudden the inline fuse to the Ranco then the compressor clutch keeps blowing.

I have a "Gardner" switch between the fuse and the Ranco, and it's been that way and functioning for years, but now when I engage the switch the fuse blows. First thing I suspected was the compressor clutch, but the same thing happens even with the compressor unplugged. I've tried powering the clutch directly through a 7.5 amp fuse and it engages with the fuse remaining intact. Another mod I have is a feed to the auxiliary fan relay (via a diode). Unplugging the relay makes no difference - fuse still blows. (I'm running out of fuses!) Relay works when tested, as does the fan.

I'm out of ideas on how to troubleshoot. Presumably the most likely cause is a short somewhere in the harness between the fuse and the compressor?

Anyone got some pointers?

 

I should probably add this is a late (87) Series 3.

 

What happens if you unplug (or bypass) the Ranco Thermo itself?

Cheers
DD

 

Yeah tried that - I've been going through everything one at a time now after taking a good look at the various wiring diagrams I have available - and taking it out causes the fuse not to blow, however that's no surprise as that leaves the feed from the fuse going nowhere (nothing to cause a short). I didn't get around to trying to bypass it, rather I started at the compressor again and unplugged everything (including the ground wire to the HSLP switch and the wire to the alternator which is on the same harness) and plugged in the Ranco again. Fuse didn't blow - so I started plugging things in again and now that it's all connected back up - no blow and everything works.

I'm thinking something had to be shorting between the Ranco and the compressor but damned if I can find any chafes in the wires. I moved the wires around quite a bit though and tie-wrapped them up again in slightly different positions. I guess time will tell!

 

What I meant...but didn't say!.... was to unplug the green/brown wire at the Ranco, thus eliminating everything downstream, leaving the Ranco itself suspect if the fuse blew again. But you've effectively done the same thing


Yeah, the 'fiddle factor' at work

Cheers
DD

 

Replace the fuse with a buzzer, leads go across the terminals. I have an old 12v buzzer I bought at radio shack years ago. It will buzz while the short exists. You can root around and tinker and when the short no longer exist the buzzer will stop.


I put tape over the buzzer hole to get the sound level appropriate for the situation.


https://www.radioshack.com/products/...FUiHswodYfIHPQ

 

That's such an excellent idea! I'll definitely use that in the future.