A/c manifold gauge hookup questions

[Frostbite]

I know its late in the season but i want to fix my a/c on my 1973 duster. I have done alot of a/c repairs on r134 systems and never any on r12. I ordered a new manifold gauge that has r12 hook ups. I rember when i was getting a/c training in college on old r12 systems one has to be careful hooking up gauges because both low side and high side has the same size fitting.

So havnt gotten an a/c diagram out to compare to see which is which but i figure here best place to get a fast answer.

i know theres a fitting on the passenger side of the compressor pump and one on the a/c line out of the pump on the driver side. Which is which?

 

[Ges2343]

High side is always the side which has the smaller hose going to the condenser . It's no big deal if you hook them up backwards. Other than you will lose a little refridgerant switching them back. Why not retrofit it. If. It's not working you probably have a leak. R12 is pricey if you can find it.

 

[67Dart273]

Well yeah, it IS a big deal if you hook 'em up backwards, because the head pressure will probably peg the low side gauge.

On newer systems, the R12 hi side fitting is smaller than the "standard gauge" 1/4" flare, I would guess it's a no3 or 3/16 flare. You can, or could, buy adaptors


Just "follow the lines." If you start at the compressor, one tube should be LARGER. This is always the suction. Any question, follow one of 'em from the compressor, the small line should go directly to the condenser. On older systems, sometimes the high side fitting was on the dryer/ receiver which is AFTER the condenser.