Why is the AC/start fuse blowing on 1999 Dodge Ram Wagon 2500

When the switchpasses thru AC, it blows the fuse, thus vehicle will not start, and no cold air also before fuse blows.

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2 answers
Fuse #2 (10amp) in the Junction Block powers the Coil side of the A/C Clutch relay. Fuse #5 (20amp) in the Power distribution Center (PDC) under the hood powers the contact side of the A/C Clutch relay AND the contact side of the Starter Motor Relay. Superbob is correct in making sure your A/C Compressor Clutch coil is not shorted or drawing excessive current.
First thing I'd check is for a shorted A/C compressor clutch. Find the wiring to the compressor, unplug the connector to the A/C clutch, and see if it fixes it. You may want to find an auto electric specialist or a Dodge/Chrysler specialist.
If you want to find a specialist, here's a directory link for you:
https://repairpal.com/directory?address=35760&car_brand_names=Dodge