Automotive Air Conditioning Information Forum

Sounds like you have a nice "tight", leak-free system. A vent temp of 42°F at a 90°F ambient is excellent, especially for a C5. Here's hoping it'll last a good long time, as you mentioned.

My goal is to run it off a belt driven compressor, I’ve plumbed all the lines but have not yet tried to draw a vacuum and/or charge the system. Taking my time so I don’t make a co$tly mistake.
A belt-driven compressor should work.

If you haven't already done so, I would remove the TXV, inspect ...

First of all, I presume that your truck did not have factory-installed A/C. If that presumption is correct, then it seems that you installed one of two Classic Auto Air kits:

1. 1973-79 Ford Truck Non Factory Air - Model Specific Fit Elite Series, SKU 20-2095
2. 1973-79 Ford Truck Non Factory Air ...

As far as I know, the Parkomat system was primarily designed to cool the sleeper cabin of a tractor/trailer without the engine running to minimize noise and fuel waste. The compressor, I believe, was electrically driven by an integral motor and powered by a lead-acid battery. Other than that, the ...

Be sure to let us know how you make out.

It has been on R134a for 20 years. That is not the problem. But good point!
I don't know your car's service history (not much, anyway). But if the compressor is the original since the system's conversion to R-134a, and even before that (it could be a GM R4, which isn't known to be the greatest ...

1987 Sunbird, when I switch on the ac button to activate compressor there is immediately a loud screeching sound from the comp area. It stops after about 7-8 seconds. Vents put out ice cold ac. Then, every about 5 minutes the sound comes back, then again, goes away. Could it be the loose ac belt ...

Last night I played with it some more. Connected my brand new 3-port Fieldpiece manifold and all 3 brand new Yellow Jacket Plus II hoses to vacuum. Got down to 370 microns after a few mins. Shut-off pump isolation valve and shut-off pump. Today I'm at ~750 microns, so think I'm OK in regards to ...

A reading of ~500 microns, excellent for MVAC systems, is an extremely small, measured amount of vacuum that you can't even notice on a high-quality Manifold Gauge Set's low-side gauge in Inches of Mercury (InHg). That said, temperature, pressure, and material composition can also affect outgassing ...

Outside of the historical link you provided, I'm unable to help with anything related to the Mark IV (documentation, photos, templates, etc.). However, I do want to acknowledge your posts and wish you all the best with your project.