Automotive Air Conditioning Information Forum

I’m working on a 1978 Lincoln Continental Mark V. Has anyone dealt with a system with no dedicated low-side (suction) gauge port valve? The system has a high-side port in the liquid line, and uses a throttle suction valve (POA) to maintain a minimum pressure in the evaporator (as I understand it). The POA valve has a gauge port...but won’t it just measure the pressure it’s maintaining in the evaporator (28.5 psi at sea level)? I have the factory service manuals and other systems of that year show a dedicated low-side port in addition to the port on the POA valve. I’m not missing any parts and photos online and in the manual indicate there is no other gauge port. My question is how will I measure the low-side with my manifold set. If it matters I’m keeping the system R12 and using an A6 compressor. It’s apart right now so I can’t take measurements. I appreciate any help; I’m stumped.
Thanks,
Mike

The evaporator pressure is all you need to measure in that system.

The low side pressure at the compressor suction port will be all over the place as the POA valve does it's job. It would be meaningless.

Keeping that car R12 is an excellent idea. If it is empty right now I would check the oil level in the compressor sump, and replace the dryer. MAke sure the fan clutch is in good shape.

Charge it using the sight glass with R12, monitor with your gauges.

Ok that explains it. I’m replacing the compressor, TXV valve and dryer, flushing the evaporator, condenser and lines. Thanks for the help, feeling better about it now.