W126 Hi-Side AC Test Port: Size?
 

Hi,. my car ('86 420) has a low-pressure r-134-A adaptor on the high side, at the condenser, so I can't connect to the high side when testing. It has a Schrader valve in it and screws onto a male fitting, which looks like Acme threads, on the condenser tubing. At Polar, they have this part listed for the low side, and the high side is for 3/16th threads. How can I get the correct adaptor so I can connect my gauge set to the high side?

Any local auto store should have proper 134A fittings. Be aware, 134A doesn't cool well in a warm climate.

Believe me, no local parts store can touch this part, I have tried. It's not the quick-connect adaptor, it' s the part that attaches permanently to the fitting on the condenser, that I need. For some reason, whoever converted the car to R134-A years before I bought it, did not have the correct high-side R-134A fitting, so they screwed on a low-side fitting. I see they removed the Schrader valve from the factory fitting, then screwed this fitting on; it contains it's own Schrader valve. The low side of the gauge set will connect to it, not the high side.
What I need to know is: what size is the OEM fitting on the condenser, then I can ask for the correct adaptor/test port.

In this case, couldn't you purchase another Low Side hose and connect it to the condenser and the high side on your gauge manifold?
Just a thought.

Exactly what I do now; thought I'd get it right, though. Maybe this is impossible.

The factory low side and the high side are the same. You can get the correct adapter for the high side from most any parts store. You may have to buy both the high and low in a kit. Some adapters have a piece in the adapter that looks like a valve but is only a rod to push the original valve. Just think, before they came out with R134, ALL a/c systems used the same fittings. One set of gauges was all you needed. Now you never know what you need.

Good luck,
Paul