AC fuse blows - 91 L98 manual air

[gbrtng]

This one's got me stumped - the AC fuse blows when ignition switch is in the run position. That's with the AC off, doors closed, etc. The FSM shows several other circuits powered by this fuse including the CCM, the AC control head, the AC programmer and several other relays.
I'm looking at page 8A-11-4 of the FSM electrical supplement.

Before I tear into the dash assembly, does anybody have an idea where to start looking? A generally unreliable component?

Breaking the circuits apart at splice S238 looks like the last chance.

Thanks,
Glenn

 

[G Winter]

looks like your manual is the same as my 90.
I would be looking at the left side of the page , engine and rear defrost.
C 100 looks like a connection page 8A-201-7 figure 20
You could also try disconnecting the O2 sensors, they are heated.Maybe shorted ?
Rear window defrost if you have it , I didn't dig into that but should have a relay.

Glenn

 

[gbrtng]

Post mortem: After tearing all the components out that the A/C fuse powers, I isolated the problem in the A/C control head. I installed a used one from ebay and all is OK. I have been fighting this for over a year and it's been an intermittent problem I thought I had solved by replacing the 10 amp blade fuse with a 3AG slo-blow in a holder. That worked OK until about a month ago, and then the slo-blow would. Right away. About then the low coolant light came on too. Replacing the control head solved both problems and looking at the schematic diagrams, I have no clue what failure in the control head would ground the low coolant light circuit. I'm not going to describe the remove and replace procedure for the control head because it's pretty involved. Anybody who needs to know, PM me.

And then:
Did a disassembly of the control head and found the fan switch was worn so that two fan speeds were selected at a time. The switch is rotated CW and CCW in increments each time an up or down button is pushed, and the wear prevents the switch from rotating completely to the next position. Hope this helps the next guy, because it was a real p*sser to diagnose.