A/c manifold gauge hookup questions

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.