The other day I went out and got myself a beautiful professional A/C manifold gauge set to check the status of the A/C system on my 2004 Tahoe. As far as the proper pressures of the system are concerned the instructions on how to use the set say to follow the manufacturer's recommendations. I am confused now. I always thought that all automotive A/C systems operate within the same perimeters. A fully charged, properly working A/C system should be around 50 psi on the low side and around 250 psi on the high side +/- allowances for ambient outside temps. Is that correct? Or are these specs different for my Tahoe which has front and rear separately controlled A/C. The reading I got on my Tahoe was 60 psi on the low side and 265 psi on the high side at an outside temp of 87 F. Is that a good reading?