Heater / AC Fuse (#12 I/P fuse block) Blows 2000 Astro LS

Heater / AC fuse (#12 I/P fuse block) blows when the controls are changed to anything other than vent or the floor. I have replaced the climate controls already but problem continues. The temperature and fan speed controls all work fine until you change to anything other than vent or floor. I have had the AC compressor replaced last summer as well as the High and low pressure cut off switches.

Disconnect the A/C high pressure cut out switch, located on the rear of the compressor, and see if it still blows the fuse. If the fuse doesn't blow, follow the dark green wire to the VCM and look for a short to ground. If the fuse still blows, trace the light green wire back to the mode switch and look for a short to ground. If there is no short in the wire, the mode switch is shorted internally. Here's a link to the schematic: http://i561.photobucket.com/albums/ss58/cwhook/2000MLbodyACschematic.gif Post your results.

While you are disconnecting that switch look for grounded wires near it...Did the a/c work since it was all fixed?

That is a normally closed switch which must be seeing a ground somehow...

Ok, I disconnected the pressure switch and the fuse did not blow. I am still tracing out the wiring to look for a short.

Yes the ac has worked since the compressor and pressure switches were replaced last summer.

Check the dark green/white stripe wire from the A/C high pressure cut out switch to the VCM for a short to ground. Disconnect it from the VCM and the pressure switch and check resistance between the wire and ground. It should show infinite resistance, (open circuit). Post your results.

I disconnected clear harness (labeled "white" on VCM) and the pressure switch and check resistance to ground. Does not show a short. Could it be a bad A/C high pressure switch?

Did you check resistance of the dark green with white stripe wire from end to end? It should show less than 5 ohms. If the resistance is ok, and not shorted to ground, it is possible the that switch is shorted to ground. To test it, unplug the connector and check the resistance from both pins to ground in the switch, not the connector. Resistance should be infinite, (open circuit). Resistance from pin to pin should be less than 5 ohms.

Found high pressure switch on compressor shorted to ground. Replaced switch and recharged A/C. Works great! Thanks for all your help! :iceslolan

Cool, glad you got it fixed, and thanks for posting back with the solution.