First thanks for your replies. This Safari is built on a Magnum chassis. It is a diesel pusher powered by a Cat diesel. Static HP was 150. Ambient temp was around 90. I have a cheap set of gauges that had served me well up till now. But I have a better Mastercool set arriving today from Amazon. I ra...

I’m working on a 1999 Class A Safari Motorhome.

I have static low pressure of 30. As soon as I start it up my low pressure goes to 0. High is 150.

This is a situation I have not encountered before in my limited a/c experience.

Any suggestions on what to check would be greatly appreciated.