First off, you need to figure out where all your freon went.

Secondly, decide if you are going to refill with expensive freon or convert to the R134a or one of R12 substitutes.

Thirdly, how are you planning to pull a vacuum on the system before refilling?

Forth, why do you think you need to add oil to the system?

Fifth, the type of oil depends upon what choice you make wrt fluid selection.

Sixth, do have a manifold gage set? R12 and R134a use different connections.

Seventh, go back to question number one. Until you can make the system leak free, you are wasting your time and money doing anything else.

Servicing the A/C system requires specific tools, and you'll need to get or borrow a manifold gage set (to monitor pressures and add/remove fluid), you'll need a vacuum pump to evacuate the system (connected to the gage set). To solve the leaking riddle, you should also have a sniffer. Not a cheapo one, but one of quality. Makes a big difference, I've tried cheap...

You need to study how an A/C system works, understand the cycle, and what each component does. There is a pressure/temperature relationship, so what you are looking for on your gages will depend somewhat on the ambient temperature, as well as your fluid choice.

Selection of the fluid will involve cost, ease of acquisition, and tools available. Best solution is to refill with (expensive) R12. Selection of another fluid may require different oil and/or gage set. Adapters are readily available to convert from R12 to R134a port connections. Different fluids will require different charge amounts.

To summarize:

Find the original leak, system needs to be pressurized
Evacuate system.
Repair/replace components as required.
Vacuum system.
Verify vacuum remains after sitting overnight.
If vacuum drops, go back to step one.
Introduce fluid of your choice into system via manifold gage
Fill with appropriate amount.
Enjoy cool A/C.

Hope this helps you get started. Often these old systems that have been sitting idle for a while will have a cascading set of failures as you try to bring them to life. IOW, you may have to go through this process more than once before you finally get a reliable system.

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles