Thanks for posting those schematics Jim. Regardless of the wire color, all cars use a full 12 volts for the high speed blower. Some use a dedicated relay. The other speeds are merely lesser voltages. The coils on the resistor block lower the voltage but then they get hot just like a toaster oven. The resistor block is placed in the blower box air stream so it cools the resistor coils. My 1972 Catalina was the first car I had that had that big 30 amp inline fuse going to the blower. It caused a lot of trouble. Anyway, the secret to cold AC is to have absolutely NO moisture in the system. Read this article it is a good one: How automotive AC works The orifice or expansion valve where the high pressure liquid becomes low pressure vapor, and the temperature drop occurs, is where any moisture will freeze and block the system. Any time the system is open to the atmosphere you must assume moisture has entered. This why we vacuum down the system after it has been opened. You use a vacuum pump to bring the vacuum down to 29" at which point water will boil. Any water vapor gets drawn out by the pump. The receiver/drier will catch any moisture that may still be in there after servicing. That is why it gets changed out for a new one when the system is opened. You absolutely need a manifold gauge set so you can test the pressures. It is also used to vacuum the system as well as to add freon. The days of 'just keep adding until it feels cold' are long gone. Now we measure out the EXACT amount of freon the system takes. I use a simple cheap digital Postal scale for this. If you do all that, and there are no other problems, then the working pressures will be what the FSM specifies. When I said start testing for leaks I meant the evaporator in the AC housing, and the condenser in front of the radiator. Seal the ends and put a vacuum on them and see if it holds. If good, you can re-use them. A commercial AC flush might be a good idea too since they are so old. Then you can start with the correct amount of fresh oil too. The only moving part in the system is the compressor. It will either work without leaking- or it won't. Luckily the big GM A6 is a very good unit. Here is where it gets tricky. The system uses special oil. The old R12 system used mineral oil. Modern R134a systems use PAG oil. They are NOT compatible! So if you can get any R12 [EXPENSIVE] or equivalent, to use in your original R12 system you can stick with the mineral oil. If you want to change to R134a you must either flush or replace everything so the PAG oil can be used. Converting to R134a is well documented and tons of information is available. Trust me, it gets complicated. I know, your eyes hurt by now, last thing. I have a 1983 Pontiac G-body station wagon. It was R12. I am using all the 40 year old original parts, even the original mineral oil, except for the new drier and the compressor which is a 4 Seasons re-built. How? I used a freon replacement called Enviro-Safe. Enviro-safe freonThey now have to call it an R134a replacement because it is illegal to sell an R12 replacement. But it works fine in an R12 system because it is compatible with mineral oil. The commercial standard is 20° below ambient. I shoot for 30° below ambient and I sometimes get 35° below ambient. I am very happy with it and no conversion needed. Whew. My fingers hurt. Later.
