How to tell if compressor is bad

This particular compressor is only building up air pressure if your running the engine at more than 1500 rpm. I took the discharge line(to dryer) off at the compressor and its only lightly puffing air out. I replaced the governor with 3 different ones, two Benedix one part smart. Same results. It's on a m11 cummins. So took the same line off of another truck and that compressor is pushing a lot of air out. Another reason I think it could be the compressor, the driver dumped air antifreeze into the compressor fresh air intake line last week when the truck had ice in the lines. So I guess my ?s are if there's another good/better way to test the compressor, and if dumping that alcohol in through the intake is what could've done it in. Thanks

 

I'm unsure of model tonight, I can report bk with that tomorrow. Driver said he had dumped close to 3 qts through intake. I was thinking that could be too much and not really wanto compress, but I guess I thought of compressor more so of a pump, not really compressing bc there's nothing to fire the pisytons bk down /gear driven. I can see how it could've knocked some crud loose. By removing the cover, do you mean the head? The "top" plate on the compressor? I believe I'd end up having to remove engine intake manifold unless the bolts are shorter than 1". I did remove intake hose to compressor, no difference in air coming out. It does puff continuous air, just not any real pressure, and I removed hose from dryer to tanks, and since there's hardly any pressure entering dryer, hardly any coming out of dryer. I also had replaced the dryer, as a whole unit, not just cartridge. Along with three different governors. I forgot to add in the first post that after running for a road test, the final governor quit allowing compressor to pump at all. I adjusted governor and now builds up to 140psi. But no difference in pressure coming out of compressor. (Whew, that was a lot to type) . Thanks for replies, any more help/input is greatly appreciated.

 

I'm assuming it wasn't all at once. Actually about impossible. But if he ccontinuously added, would it cause some type of failure?