Tom,
I swapped the FRIGC fitting for a standard quick disconnect fitting before starting the engine and ran a gauge on the low side while the engine was running and the compressor was turning, and got zero PSI.

I was looking to see what the high side pressure was and to establish whether the tech that did the conversion had put a quick-disconnect fiting on the port. He did not.

Now that you verified where the high side port is, what I found there last night was a flimsy hex-shaped metal cap that had all but rusted off.

Removing the cap revealed a fitting that was still under some pressure when I loosened it a tad, but it looks like I'll have to depressurize the system and put a quick disconnect fitting on it at some point in order to monitor system pressures when I do the recharge.

BTW, I have done a successful R134 conversion on my F-250, and am not afraid of this project.

__________________
Nate Stanley
(Currently Benzless)
1985 F-250 6.9l 170K
2009 SCION XB 36.5K
2003 LS430 78K
2012 Kubota B 2320