Air Dryer Purging Air Every 15 Sec

[GunRunner]

So I blew air through the 1/4" line going to the compressor for the unloader valve and heard it stop pumping. I then heard large amounts of air escaping from the back of the compressor through what appeared to be a weep hole. I'm guessing the head gasket blew so I just went ahead and replaced the air compressor since I was able to get one at Fleet Pride and use a 25% off coupon. Got it swapped out and everything is back to normal. Thanks for everyone's input and suggestions and patience while helping me diagnose this. I guess I won't be going back to that shop, they had the truck for 1.5 weeks and said it needed a new compressor because it was likely the unloader valve but never told me how they diagnosed it to come to that conclusion. I'd rather do all the work myself anyways, I only had them do the air dryer initially because it was in for resealing the power divider and they said the air dryer was leaking during a DOT annual inspection.