91 1500. grinding noise coming from somewhere in the front, cant tell if engine compartment or inside cab when activating either Defrost or A/C. Anyone know what's going on? At first I thought it was the compressor until I realized it does it with defrost too. Which makes me wonder if there's "two" blower motors in this truck?

 

Had the same thing happen. I was told it was the beginning of my compressor starting to go bad. If you find out let me know.

 

You do not have two blower motors. In defrost mode your A/C compressor does run. Most likely culprit of the noise is the a/c clutch. You may be lucky and just have to replace the clutch assembly, but most likely the compressor also.

 

The a/c belt tensioners go bad also and are a common problem. remove the a/c belt and see if the tensioner is seized or the tensioner pulley is worn. Spin the A/C compressor pulley while the belt is off to see if it is has play or has bad bearings.

 

Hey, I finally got around to replacing the A/C tensioner and tensioner pulley, and that fixed it.