air conditioner just started to blow hot air...

The best approach is to visually inspect the air condition system to include ensuring all fuses and relays are functioning properly and the compressor has power. If the electrical assessment does not uncover any issues, the next step is to determine the refrigerant levels, vacuum test the system to determine if a leak exist and recharge with the proper quantity of R134a with dye. If the refrigerant level is too high or too low, the compressor will not function properly or not at all. Once this process is complete with the proper equipment the low and high pressure readings can be monitored to determine if the system is operating correctly. I hope this helps...