[Jack Houpe]

That makes sense. Is there any way to check to see if it's actually bad or should I just replace it?

If I need to replace it, is there anywhere to find out what part number I need?

Just for sake of understanding, the engine compressor should supply air to the reservoir tank for the airbags. But because it's not, using the 120 air compressor should do the same and it's just another avenue that would bi pass the PPV valve and possibly other components that may be an issue here?

From my understanding if you can get the 120v compressor running it should raise the coach with the key on and in one of the modes like travel. The PPV valve should pass air in both directions IF there is no problem down stream of it. Suppling air pressure from the 120v compressor may dislodge it but if its 27 years old and stuck now I would not trust it even if it did free up. I can't tell you the part number but you could call Newell and perhaps they could tell you. Jack stands are needed to do this safely or cribbing. You will need to determine if you have a major air leak or if the PPV valve is stuck, I would not bypass it I'd just take it out and replace it. If you get the 120v compressor going and the coach raises and holds pressure its the PPV valve for sure. The little 12v compressor is mainly to flush the air toilet or open and close air doors. I am not experienced in this system yet but have watched Richards videos and he explains it well.