The other day I had posted here on info about the AC on a 4450. It has the original Nipendenso compressor R12 fittings but I have a conversion fitting to use my 134a gauges. I had found a leak and corrected that. Pressurized the system with my shop air to 100 lbs from a adaptor that I had made then snapped on my AC gauges and closed the LOW pressure valve and watched the gauge for almost 2 hrs. No movement on the gauge. So, I assume no leaks right ? This is all with the tractor not running. Should I have it running or will the compressor run with just shop air pressure ? I'm thinking it shouldn't but I've been wrong before. Any insight on this subject? I want to make sure that all leaks have been corrected before I charge the system with 134a. I had tried to vacuum the system for a hour but it would go down to negative five psi for a short while then the gauge would go up to a positive 7-8 then repeat. It would still hold 100 psi for 2 hrs tho...