The testing of the switches I am not sure of but as far as my escapades went i had to replace them because with a full charge my A/C compressor would not engage.

I thought I had a leak which I am pretty sure I never did.

Those 2 gages read pressure and a seperate pressure(same as temp which is funny from what I have read) that is safety for the compressor so it never runs without Refrigerant to keep it from burning up.

Its silly he replaced the evap but left the dryer old in the system.

I suggest you order the 2 sensors (about 25 bucks total) and charge it up and see what happens.

I did it best A/C ever in my car as things go.