without even looking at the car, that the evaporator is leaking. If it has not been used for a year (who knows) the compressor may be on the way out too.
The only way you can find a evaporator leak (100% sure) is with dye.
What I would do, have the A/C fixed and convert to R134 at the time with a good warranty and then renegotiate the price. The odometer should be the least of your worries, compared to the A/C, these cars will last a long time with proper maintenance. Let him show you papers.
Ask him what is he going to do if he does not sell it to you...
It may be worth more as a parts car, and I need a couple!
What color is it? Just curious.