How to Charge Auto AC Systems

Charging the AC process after a repair requires a vacuum to be created in the process to remove moisture. As the vacuum develops as well as a negative pressure is felt, the boiling point of moisture is lowered. This enables any moisture to turn to vapor and be removed by the vacuum pump. This step is critical to the success of your AC process repair. A nice set of gauges as well as a vacuum pump is necessary to accomplish this task.

Instructions

1 Attach the gauges to the system service ports. The blue hose is for the low-pressure side, the red hose is for the high-pressure side, and the yellow hose is for attaching the vacuum pump or a refrigerant can tap. To identify the low-pressure service port, follow the larger of the two lines attached to the back of the compressor. The port will be located on that line, somewhere between the compressor and the drier mounted to the evaporator near the firewall. The high-pressure service port will be located on the smaller of the two lines, between the condenser (mounted in front of the radiator) and the evaporator located near the firewall.

2 Attach the vacuum pump to the remaining yellow hose. The vacuum pump is normally electric, but there are a few air-powered units available. Turn the pump on if it is electric, or attach the pump to an air hose if you have an air-powered unit, and let it run for an hour. During this time vacuum will be pulled on the system and any moisture will be vaporized and removed by the pump.

3 Test for leaks by closing both valves on the gauges, and allowing it to sit for five minutes. The vacuum should not drop during this time. If it does, there is a leak in the system. If the vacuum remains stable, the system is ready to fill.

4 Remove the vacuum pump from the yellow hose, and attach a can tap. Install a can of refrigerant on the tap, and twist the thumb screw all the way in and all the way out to open the can. Start the engine and set the AC controls to medium blower speed and max AC. Open the blue low side valve and add refrigerant. Be sure to close the valve when changing cans, and at the end of the process.

Tips & Warnings
Using refrigerant with dye added makes finding leaks simpler.
Typical cans of refrigerant are 12 oz. & not one lb.