Have you looked at the wiring diagram on the firstgensite. They have one specific for the AC system. Don't think it is the resisters because they get bypassed on High and 12V is put directly to the blower. If I had to guess I would say it is in the switch itself, but I would jumper around the switch to mimic Hi (e.g. jumper Brown to Black-Orange Stripe). If it continues to run (after 30 seconds), it is likely in the switch itself.
With the symptoms, I wonder if someone replaced the inline fuse with an automatic reset breaker?
