Where is the low pressure air conditioning service port located on a 1991 E-350

 

This may help. Had the same problem on my 90 E250, 460 V8. Finally spoke with a mechanic that knew what he was doing. On my vehicle, I had to remove the entire air cleaner assembly to get access. It was not that hard to do. Once removed I still could not see the low side schrader valve but the suction line runs under the windshield cowl across the vehicle and when you run your hand along the suction line you will feel the valve. It is located under the center of the windshield. Hope this helps.

 

Thank you Bamlin54 for helping me locate the low pressure port. I spent two days trying to find it.

Thank you again.