I wanted to determine the amount of freon I have in my system. I unscrewed the low pressure valve on the front passenger side, and engaged my measurement meter. I started the car, turned the a/c on max, even put the recirc button ON. I checked the levels, and it would cycle from a low of 15 psi, then a click, to 40 psi. Then back to 15 in the next 2-3 seconds, and then after 3-4 seconds up to 40 psi. I guess the compressor is cycling. Which is the correct reading of the pressure? If 15psi , I need more freon. If 40psi is correct reading then I have a larger a/c issue.

Note: The car is basically undriveable wihout a/c imho.

TIA,
Lunchman.
95 850 Turbo, 156,000