Freon Capacity?
 

Anyone know the freon capacity on the a/c system for a 1981 F150 4x4 with a 351M & C6?

It may be gone, but there should have been a sticker on the radiator support. Unfortunately, most of the computerised manuals only go back to 1983.

I wouldn't think that the AC systems varied in capacity based on engine size...

FWIW, my 81 F150 with a 302/C6, 2WD and factory AC has a sticker stating that it will hold 3lbs 12oz of R12. Not sure how much R134a it will need though.

I know they vary between Diesel and gas.

^ Thanks for the correction.

Should be around 3 if it's completely empty

Truthfully I never worry about lbs. I just get the presure right and letter go.

3 cans I meant

Understood. Also if the system is dry pull a vacuum on it for at least 30 minutes and the first thing in should be a can of oil charge. I assume you know how the freon got out and have repaired the leaks. new orifice tube etc..