My first thing I always do is start pulling fuses but I would triple check that harness and check the wires going into it and see if maybe one got loose in the process of the head unit install. Otherwise it could just be coincidence and you need freon,compressor,etc.

 

I pulled out all te fuses and they all looked fine. Took out the radio and checked all the wires but they all seem fine as well. Anything else I can check? I really don't want to go to the mechanic for this.

 

Well next thing I would do is turn on your car turn on the A/C, then pop the hood and look for your A/C compressor which would be on the passenger side of the engine bay. Then while looking at it see if the inner pully is rotating. While our A/C is off the outer ring of the pulley should only be spinning, when its on the whole pulley should turn (A/C compressor clutch). If it is not then your compressor is not activating. I would then get a Refrigerant gauge you can either get one that is attached to a can of R-134 or like I prefer get a seperate gauge on a piece of hose. You would attach that to the low side of your system which would be a metal tube coming from the a/c compressor and it would have a little attachment on the tube (kind of like a tire valve on your tires) that you would hook that hose up and check the freon level with your car on, A/C on fan speed max. That would determine if you are low on refrigerant. If that isn't specific enough I can look at my XRS motor and try and get some pictures.