I have a 2004 Chevy Trailblazer XLT. The AC on the drivers side only was blowing warm air. I took it in thinking I may need a charge and was told the blend door on drivers side needed to be replaced. The following day I was told that after they removed the dashboard they see a broken door on the Passenger side and that would need to be replaced and would cost $287. I advised I did not have a problem on the passenger side and was told the door is broken and I would have a problem. I authorized the work - it cost over $800 in which according to the invoice they replaced 2 blend door actuators - ea costing $287. After all of this my drivers side vents were not blowing at all and the heat on the passenger side is no longer working and none of the bottom vents on the drivers or passenger side are blowing.
I am a single mom with 2 kids and unfortuantely lack knowledge when it comes to anything mechanical in my vehicle. Any input you can give me on how these things work and why now I would have additional problems with heat on one side not working and lower vents not blowing would be greatly appreciated and helpful.

I was also told that my battery needed to be changed as it was not strong enough to run the compressor. Would that be true? I never have a problem starting up my truck. Does the battery even run the compressor?

Thanks for your help

Jenine