2003 VW jetta stereo and a/c not working?

After market stereo installed about a year ago, the person who installed it said they had to disconnected the handbrake/sensor to hook it up. Everything was fine until it was sent in to have the rear brakes done. The mechanic said they reconnected the handbrake/sensor while repairing the rest. Ever since then both the stereo and A/C have not worked. The fan still comes on with the a/c but the air is hot. Yesterday, I pulled the handbrake up while the a/c fan was on and and suddenly cold air was coming out. It worked for the next 6 hours or so, the car was turned on and off a number of times during this. But this morning when I turned it on, nothing but hot air. I tried the handbrake again but nothing. Stereo wouldn't turn on during any of this time. Should the handbrake/sensor be disconnected again? I took it in and had the a/c recharged and filled etc but that did nothing. Any and all ideas and suggestions would be great. Thanks!