AC system is a complicated and easy at the same time
1st you need to know if the system holding in the refrigerant or if its leaking
if leaking have to check and find the leak and repair the area
many methods can be used to find the leak ,this is some

Bubble Solution Detector

This is a solution applied externally at suspected leak points. Leaking refrigerant will cause the detector to form bubbles and foam. A soap and water solution also works well.
Dye Solution
This is a colored solution that may be introduced into the A/C system. The dye will show up and color components at leak points. Some manufacturers offer refrigerant containing a Red dye. This dye-containing refrigerant is installed by normal charging procedures. Other dye solutions are visible with a Black light only.
Electronic Detector

This instrument will draw in any leaking refrigerant through a test probe, and then sound an alarm or create a flashing light if refrigerant is found. It is the most sensitive of the leak detectors used

if system if holding and no leak
know you have to check if the AC compressor coming on and what you have for pressure on low and high side
need to use a set of manifold gauges

if this part of the system check OK
know we move on to the HVAC box and the blend operation
and have to check if the blend door operating and the actuator function

Answered by BMRFIXIT (expert)
19,736 answers provided