A/C only works when 2010 Mazda CX7 is cold
 

I have a problem with my A/C, it only works when 2010 Mazda CX7 is cold and once it worms compressor and fan starts working for 2-3 seconds and then it stops for a few seconds. Today I got a chance to check low pressure side while it worked and it was around 35psi. I started adding more 134A fluid and by the time I started doing it my A/C stopped working again. I'm guessing it is currently about 40 psi on LP side. Also I tried different compressor clutch and A/C fan relay with the same problem. My car have 44k miles and it's got extended warranty. Last time dealer told me, they would charge $150 just to look at it and if the part is covered they'll replace the part for free. Here is the question, can it be a faulty thermal switch/sensor that stops A/C from working or any other sensors such as Evap, Temp, Refrigerant? Can it be compressor clutch itself?

Thank you in advance