what does the ac thermostat do and where is it located?

What is your question?

My ac started blowing hot air. I had a new ac compressor installed because I was told the seal blew out and lost the refridgerant. After that the AC still blew hot air. I was then told that there is a thermostat in the evaporator compartment and it had to be replaced. What is the purpose of this thermostat?