Engine Noise

[GMCTruck]

Ok this thing is creeping me out... i know my A/C needs recharged... but this is the problem im having i got a 94 sonoma 4.3 and every time i engage heater or just blower eather one... when i turn the dial to anything else but off something underneath the hood makes a noise every like 10 seconds like some motor or something comes on.... almost like a shattering or weird vibration.... any clue as to what this could be.... scared to turn the heater on... but its getting cold lol ....

[Metz Motorsports]

In most GM vehicles it is design that the AC compressor comes on when using the defrost, or even the heating system, designed to take the moisture out of the interior cabin. Just what I have heard.....HTH

 

-Jason