I had to replace my heater core this last winter and I'm just now getting around to charging my ac system since I haven't been driving the jeep much. My question is does it need to be done by a shop or can I buy one of those recharge kits and do it that way?

 

If the system has been opened, it really needs to have a vacuum applied to it to get all the unwanted stuff out. If the "freon" has leaked out, but the system hasn't been opened, you can just recharge it since it generally doesn't suck air in, only letting the pressurized "freon" out...

 

Did you disconnect the evaporator when you did the core? If so, as Jim says, it needs to be evacuated before charging. Depending on other factors (how long was it open, etc.), PAG oil is hydroscopic (attracts moisture) so you may need to flush the system to get the old, contaminated oil out, leak test, then recharge.

A shop can hook up and do all of that and ensure your AC works at peak efficiency will cost you. You may want to get a few quotes before you decide.

You can DIY it, if you have the vacuum pump (electric or compressor driven) and a set of manifold gauges.

I service my own when needed.