I just pieced the a/c system back on my 69 Malibu. All new components on the original system. I had he POA valve re-calibrated for R134 and changed the oil in the compressor.

I'm ready to take it to the shop to have the system charged.

Is it ok to run the belt on the compressor before it's charged as long as I don't power it up?

How much refrigerant does the system required?

Sure, put the belt on, the pulley free wheels.
Even if you were to turn it on, the low pressure cut out switch won't let the compressor clutch engage.

I Have been putting in 85% or so of the original charge lately when converting to R134A but I have had a couple of systems that I put 100% of the original charge and they seemed to work better.

You shop will know by the operating pressures.

Excellent. Thank you, Dean.

Ditto what Dean said,
Also, if your fan clutch is "old", replace it with a new AC Delco unit. An "old" original OEM or "new" aftermarket clutch will keep the engine cool enough, but it WILL make the converted original AC system "wheeze out" at low speeds or idle. The fan clutch needs to be 100% to draw enough air across the condenser.

Good call on the POA valve. That will make the difference between the system working "ok" and working "good". :thumbsup:

Thanks for that info. The clutch fan is old but so far has been doing a good job of keeping the engine cool. It's a 350 with an aluminum radiator. I'll invest in a new fan clutch as well.