I’ve replaced the faulty part on the gas tank twice now myself and I didn’t even pop the hood.
Even if they disconnected your battery (and they may very well have a policy that requires them to disconnect the battery when working on anything fuel related) they shouldn’t have touched the AC.
If it’s just not blowing cold but the blower is still pushing ambient temp air (and the AC compressor isn’t kicking on) i would start with checking the AC fuse. Possibly the 15 amp fuse in position 27 in the engine compartment fuse box (That’s where it should be but I’d verify that in your owners manual).
If your AC was on when they reconnected your battery and the ignition was somehow switched on so it fired up your AC, I could maybe see that popping a fuse.
That would be my first go-to.
Note: this is only possibly the problem if the AC is not turning on at all (Vents working but AC compressor not turning on).