Basic because it applies to more than one vehicle I am working with, and only one is a Ford. Irealize some differences, but this is only about charge, so should be about the same.
Anyway, wat the question is : If the charge is correct, will the system need to cycle off regularly while in use? Should I be able to run a system by supplying power to the compressor, and using the limit switches to keep from going too high or low?
Situation is this: my Plymouth van has decided not to power the compressor any more, apparently in the body control module. Second part is the 92 F350 is a non-air truck I would like to add air to, and as far as I am aware, back then there weren't any modules on the trucks. Am I correct in my thinking that they just supplied power to the clutch, and it only cut out when the pressures were off?

 

Way more than a "basic" ac qustion, but I'll try.

On the Plymouth: Sounds like you have EATC. The BCM driver for the AC relay was a comon failure. Later BCMs were more robust in the AC relay area. There is no good work around to make the AC work without problems. If you bypass the BCM, the evaporator can freeze up or the high side pressure can get high enough to trash the compressor. If you bypass the BCM it will cool like a meat locker for a short time, then...? If you're good with electrical systems , you "could" totally rewire the system to work differently than designed. But that would be more hassle than replacing the BCM. The junkyard will be your friend here, as long as it's older than about a 1998 or so. Newer than that, and even a used BCM needs to be programmed by the dealer IIRC.
If your 92 F-350 didn't have factory AC, look for an aftermarket "dealer add on" system. Adding factory AC "can" be done, but IIRC you need to carve open the firewall for the evaporator box. At minimum, you would need the entire system, down to the IP controls, from a donor truck.

 

Actually, the F350 is easy, the evaporator was a simple bolt on deal, the regular non air and the a/c mount exactly the same. I'll have to scope for the panel button and controls, but the hot/cold **** is the same, only visual difference is the button to push to turn the compressor on.

 

I could be mistaken about the firewall. I haven't seen a non-AC truck of that vintge in quite some time, but I seem to recall there being a difference in the passages through the firewall.
If, as you say, the evaporator is a bolt on, then adding AC from a donor is actually quite easy. You will need to change the control head though, due to the switch. The wiring will be there in the main dash harness and possibly tthe harness out under the hood. (Look for an unused cycling switch connector near the passenger side firewall to find out) I've done this swap on older Escorts, Tempos, and Rangers and it was a weekend project with a donor available.

 

I snagged the wiring from the 86 that I got the evaporator from, at least the under hood wires, just have to work on the dash part. The blend control is vacuum actuated as well.
Now kick back a few years to the High Output heaters, which were non a/c, then nothing trades without a bit of work.
I'll have to go over to a friend's salvage yard, he has a few 87 up trucks with a/c. I can get the dash wiring parts that way.