Refrigerant capacity on dealer air?

[oldiron]

Anyone know the refrigerant charge on the old r12 dealer air systems? In ounces.
Greg

 

[Rustytruck]

in lieu of a charge spec the old systems had a sight window in the top of the receiver/dryer or in the line so you charged until the bubbles in the fluid went away. it is wise to watch the head pressure too.

 

[56f100bbw]

Just like Rusty said

 

[Broncobowsher]

But R134a (which you will probably be using) is known to have some small bubbles in the sight glass even at the correct charge.

I go off superheat method (I think that is the correct name for it). You look at the low side pressure and the low side temperature of the suction line going into the compressor. For a given pressure there is a temperature the refrigerant will boil at. When you get down to 5-7° above the boil point at the pressure, you are full. Any more and you risk pulling liquid into the compressor, that is bad. You can hydrolock a compressor like an engine. If it doesn't go boom, it tends to damage the valves in the compressor.

 

[blubuckaroo]

Using R12, you can feel the inlet and outlet of the evaporator, and when both feel the same, it’s charged. BUT… a 134a system is much more sensitive than an old R12 to overcharge. The head pressure goes up fast! My Vintage Air 134a system calls for 2.8 pounds.

 

[Broncobowsher]

The diameter and length of the liquid line will have a large influence to the system needs. That line is (or should be) solid filled with refrigerant from the bottom of the condenser to the expansion valve.

Using R12, you can feel the inlet and outlet of the evaporator, and when both feel the same, it’s charged. BUT… a 134a system is much more sensitive than an old R12 to overcharge. The head pressure goes up fast! My Vintage Air 134a system calls for 2.8 pounds.

That is the same as I described above. Just by feel instead of gauges. The level of cold at the start of the evaporator, after the expansion valve is the temperature of the boiling refrigerant. Feeling the temp on the suction line will tell of there is enough boiling refrigerant inside the evaporator. You want it cold, but not exactly the same. A few degrees warmer just so it is all gas. That cold gas going into the compressor is good for it. Helps cool the compressor.

 

[oldiron]

Got it done. One of the older mechanics at the shop suggested something very similar. He said to charge until the suction line at the compressor starts to sweat. All total that happened at 22 ounces. Seems good so far. Thanks for the replies.
Greg