All you need is a dial-a-charge to weigh the charge out. It's either R22 or R134A. It's is just like an ice machine. The ice machines I have worked on didn't come from the factory with service valves. you had to drain the unit then solder them in. servicing it is not that big of a deal really. the true question is are you sure it's low on freon? what are the high and low side pressures?