How to Evacuate an Auto AC

by Floyd Drake III
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Evacuating, or discharging an automobile (auto) air conditioning system (AC) is a simple process, provided the necessary tools are available. Auto air conditioning systems need to be evacuated as part of routine maintenance when the system needs to be recharged. Different automakers use a wide array of air conditioning systems and components, however these systems all perform the same basic function and follow standard air conditioning design. Don't worry if the necessary tools aren't part of your personal tool chest, as many auto supply stores rent these tools to customers for a fee.

Step 1

Connect the manifold air gauges. Manifold air gauges consist of two gauges and three hoses, one red, one blue and one yellow. The red hose attaches to the high-pressure valve and the blue hose connects to the low-pressure, or suction, valve. High-pressure valves are located on the receiver/dryer bottle attached to the compressor, with the low-pressure valve below it and slightly to the front of it. Check with the automobile's repair manual to verify the specific location of valves for your particular AC system.

Step 2

Connect the yellow line to the vacuum pump, then make sure the high and low gauges are closed. Do this by turning the red and blue knobs until closed. Refer to the manufacturer's instructions if you need additional assistance closing the gauges. Next, start the vacuum pump according to the manufacturer's instructions.

Step 3

Open the high and low-pressure valves on the air gauge. The low, or blue, side needs to show a vacuum, which reads at, or below zero. If it does not, there is a leak that needs to be corrected before moving forward. Run the pump for thirty minutes, turn the pump off and close the red and blue gauges. This completes evacuation of your automobile air conditioning system.

Step 4

Recharge and service the AC unit according to the manufacturer's suggested procedures.

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