I have a 1983 F100 with 300 L6 with the tall style york compressor with the high and low side fittings on the top of the compressor . they both are the same size. I need to know which is the high and low. They are side by side. Thanks

 

The fitting with the line to the condenser is the high side. The fitting with the line to the evaporator is the low side.
To open the system to the ports you have to partially open the service valves under the metal caps. You will need a 1/4" or 5/16" square box wrench to open the valves. Do not use a crescent wrench or other tool of that type, you will round the stems off.
Do Not fully seat (fully inward) the high side service valve with the compressor running, you could be injured if the compressor ruptures.

 

how exactly do you open the service valves? thanks

 

You turn them, in or out.

If you have a can or two of refrigerant from the parts store with a little gauge on top, you need to STOP right now before you possibly get hurt!
No disrespect intended, but you are dealing with a "real" AC system that will cause you serious bodily harm if you don't know what you are doing.
This is not a modern Cycling Clutch system that is "I'll try this" resistant. There is a very real possibility of feeding pressure back into that can and it exploding in your hand or a compressor explosion if you don't know what you are doing or have the proper tools.
I had an explanation of servicing that system written but erred on the side of caution and didn't post it. I can't cover all of the whys and wherefores without writing a book, and don't want to see you get hurt over a detail that I missed.
If you have a proper manifold gauge set, a vacuum pump and "some" valid AC knowledge I can tell you how to proceed. If not, I won't.
I'm Sorry, my conscience won out.

To gain some great DIY knowledge, see Automotive AC Information Forum - ACKITS.COM. If you have another "modern" car to practice on before you tackle the truck, that would be great.
The system on your truck used to be the "norm" , but that system hasn't been used for 25 years. The DIY aspect has changed drastically since then.

 

I get the pump next week and already have the gauges. Just need to know how to turn the valves. I have a Haynes manual on AC and heating. It does not explain how to do so on the valves it just says you have to do It. It says to do It after you install the gauges. Thanks