The last time I had to add some refrigerant to my RV2 AC system was about 8 years ago and I've forgotten which low pressure port to use! It's a '74 B body with the original AC setup.
As R-12 is not available/affordable I'm using Hotshot 414B for refrigerant. This seems to work well.

Large line low pressure = charge side.The fittings typically cant be used backwards.Suction might also be marked on the line near compressor.Rocky

Here's the rule I always use: "high pressure side of the compressor goes to the condenser" Don't charge that side.

I always remember that C comes before E in the alphabet so the condensor is in front of the radiator and the evaporator is under the dash (rearward) and it would make sense that that the high side (high psi) would be hot (compressed from the compressor) and would be going forward to the condenser to be cooled just like the radiator cools the coolant so you would not want to open up the high side to add anything more to it cuz you are wanting to draw the freon into the system. There's only 2 ports I just dont have a mental pcture of which one is whaere at the moment but likely it'd be easy to tell when you open the hood

That and most later cars have different size ports.they made them fool proof.You cant fit the charge on a high side fitting as they are larger.Rocky

Always charge on the low side ( blue hose) The way I remember it is Red hose = high pressure side = high pressure means heat = front of the car
Blue hose = low side = cold side = rear of the car


anyway,,, I can't say for sure about 1974 ,,,but for 1969 both of the connector fitings are the same size.

Use the 1/4" male flare port that is on the large or suction side hose, not the port that is on the compressor head.

The port on the small hose is the discharge or high-side pressure fitting.

the fitting on the head is used in conjunction with the low-side or suction side fitting to evaluate performance of the POA valve internal to the RV2 compressor.