Just had my mechanic replace the hydroboost brake booster unit in my gs300. Got it back today and now my ac is blowing hot. I know he had to do some reprogramming, and I could tell by my head unit he had to take the battery off the power. Could this be why this happened? Any advice or quick things to try before I call him up would be very helpful. Also I really don't know much about cars but I learn quick.

 

AC diagnostics is a very weak point for me but I don't see why he would mess with the AC if working on the brake booster. I can only guess he may have left something disconnected. Check for unplugged connectors and open vacuum lines before calling him/her. Also check for a blown fuse. I presume the AC was working fine before the job.

 

The A/C suction / discharge pipes run under the brake master cylinder.
Check the integrity of the A/C pipes all the way from the compressor / condenser units to the cabin firewall entry port.
There is a chance of inadvertently damaging them.
And one of the fuse / relay boxes under the hood is right next to the brake master cylinder. Check it out too.

If everything is in order with them - it's time to connect the A/C gauge manifold to the car's service check valves and check the pressure in the OFF / ON states.
Listen for the click of the A/C compressor pulley clutch under the hood when the A/C system is turned on. Visually note the rotation of the compressor shaft.