How to Evacuate an Auto AC

by Floyd Drake IIIUpdated July 13, 2023
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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.

Things You'll Need:

  • Manifold air guages
  • Vacuum pump
  • Auto repair manual
  • Rags

1. Connect the manifold air gauges

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.

2. Connect the yellow line to the vacuum pump

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.

3. Open the high and low-pressure valves on the air gauge

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.

4. Recharge and service the AC unit

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


Proper air conditioning evacuation relies on having no leaks during the procedure. If a leak is present, begin by checking the valve hoses and connections. Improper connections and faulty equipment are common leak causes.


Helpful comments on this video:

  • This video is definitely helpful. But manifold purge is also a requirement in order to actually keep air out of the refrigerant tank. However, I don't think that matters if the old refrigerant will be recycled and new refrigerant will be used instead.
  • Great video! One thing I want to correct though—R-134a doesn't actually deplete ozone. In fact, that's why it is used today instead of R-12 (aka Freon), which had an Ozone Depletion Potential of 2,400 (R-11 has an ODP of 1).

The reason why you can't vent it is due to its Global Warming Potential (GWP; basically how much heat it absorbs from the sun and traps in the atmosphere). CO2 has a GWP of 1, which doesn't really tell us much because the GWP is defined based on CO2. R-134a has a GWP of 1,300, which means 1 gram of R-134a is equivalent to 1.3 kg of CO2 in terms of its effect on the greenhouse effect. One 12 oz can of R-134a has 340g of refrigerant, and venting all of that would be like releasing 442 kg of CO2, or almost half a metric ton. Roughly equal to 10% of the average car's annual CO2 emissions.

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