I have a potential accord I might buy and the guy took out the AC compressor to use in another car. The guy said the AC system ran well before it was taken out.

Could I merely get a used compressor from the junkyard, throw it in there. Buy a bottle of R134. Charge the system and have nice cold AC?

Where I live it's pretty dry so I wouldn't worry about moisture in the system.

 

moisture is the least of your worries. the elements..... its contaminated you would have to have a pro clean the a/c system to get all that junk that can kill your compressor but go ahead at your own risk. also you want to have it vacuumed then have the r134 put in it will help in LESS stress on the engine and better fuel economy also you need a/c manifold gauges to know exactly how your a/c system is working and how full or empty and how accurately you will fill it

 

If the hoses were left open then you would need to completely flush the whole system with acetone/ctc and nitrogen gas passing afterwards. If your condenser is multiflow then you may need to replace it because they are sometimes impossible to clean via flush. Yes you can get compressor from junkyard, get bottle of R134 and charge it but you would need specific procedure to follow