How do I check the AC pressure on these rear AC systems I can't seem to find any information about them online. The pressures with rear AC on was around 55 psi low and 265psi high. At 80 degrees outside with about 85% humidity. And with the rear AC off the pressures are lower. Does anybody know if I'm suppose to check the pressure with the rear AC on or with the rear AC off and what should the pressure be around?