Expert: autohelp - 3/25/2010

Question
I am trying to figure out where the low pressure port is on a 1990 cadillac seville. The a/c is empty of r-12 and i bought a kit to change it to the r-134a but i want to make absolutely sure i put the new fittings on the right ports. all the kit says is that the low pressure port is the one between the compressor and the evaporator but as far as i can tell no line runs directly from the compressor to the evaporator. i've found one port on the accumulator-drier and one on the small line up by the firewall on the drivers side. can you tell me which is which. i just want to be absolutely sure. thankyou

Answer
The one on the RECEIVER/DRIER is the LOW port.  The one on the small line is the HIGH PORT.

You cannot use R-134a in a Cadillac R-12 A/C system due to the incapability of the low pressure sensor which will in most cases cause the CHECK ENGINE light to illuminate as the low pressure sensor is NOT calibrated for R-134a freon.