I'm repairing the a/c on my 91 240. Got the compressor at autozone ($199) the condenser at discount autoparts (godan:$135) the rec/dryer, orings, expansion valve at newandusedvolvoparts.com. The compressor has 5.1 oz of mineral oil in it for r-12, and r-12 is what i'm going to use. My question: Anyone know what the total mineral oil amount should be for a 91 volvo, and what the r-12 capacity is for that system assuming a completely empty system? Thanks.

Can't help you with capacity, but suggest that you re-think the R-12 decision. The R-134 conversion kit for your car, including a new receiver-dryer (which you probably need anyway), o-rings, and ester oil, is less than $100. Get a refund on the recv/dry you bought. Instead of the stock expansion valve, buy a variable orifice valve for better low-end cooling (Rafael Riverol just did this with great success) and fill with R-134. On the fill savings alone you can pay for much of this job, and if you inject the correct quantity of R134 your cooling will not suffer at all. See the 700/900 FAQ for Dave Urban's discussion of this procedure, which is easy.

The new compressor can be used with R-134 by merely draining the oil and refilling with the Volvo ester oil. If you replace the receiver-dryer, then fill as though you replaced the entire a/c system. Otherwise, use the lesser amount for "compressor replacement only"

I can get r-12 for $14 a can at autozone, the r-134a is about $5 so the savings is only about $30. I'm sticking to r-12 because i've heard that the cooling capacity is already somewhat limited on the 240 ac systems even with r-12, the compressor is already loaded with the mineral oil and I don't know about compatability between this compressor and r-134a, I don't want to change every o-ring, I've read about long term problems with both pag and ester oils, I'm so far into this project with the notion of using r-12 that I'm being stubborn and sticking with it. Had I read your post earlier or realized how much componentry i was going to have to replace, I probably would have gone with 134.