renting a vacuum pump is going to be a waste of money. It will cost you more to rent one and refill the system yourself since if you evacuate the system you are going to need approximately 3 cans or 134. The way I see it if you want to do it the cheap way add a can of refrigerant and see what happens. If not it would be economically more viable to have the shop do it. On the other hand if you want to do it yourself, you see yourself doing this again and you don't mind investing in tools then purchase a pump and gauges and your good to go.