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System Evacuation

CAUTION:
  • Air conditioning refrigerant or lubricant vapor can irritate your eyes, nose, or throat.
  • Be careful when connecting service equipment.
  • Do not breathe refrigerant or vapor.
NOTE:
  • If accidental system discharge occurs, ventilate the work area before resuming service.
  • Additional health and safety information may be obtained from the refrigerant and lubricant manufacturers.
  • Do not allow moisture to contaminate the A/C system oil. Moisture in the oil is difficult to remove, and it can damage the A/C compressor.
  • Using a compact electrical vacuum gauge may decrease the required evacuation time because you can measure actual moisture removal with this tool.

A more efficient way to measure moisture removal is with a special tool called a compact electrical vacuum gauge, measuring vacuum levels in microns.

Connect the tool according to the manufacturers instructions and allow the vacuum pump to run until the gauge reads 700 - 750 microns (29.89 inHg).

    Shut off and isolate the vacuum pump, then observe the gauge reading:

  • If the vacuum level remains stable for at least three minutes, all moisture in the system has been removed.
  • A slow increase in the micron reading means there is still moisture boiling out of the system. Restart the vacuum pump and continue evacuating.
  • A quicker increase of micron levels indicates a leak is present in the system or your service equipment. Determine the cause and correct the leak before continuing.
  1. When an A/C system has been opened to the atmosphere, such as during installation or repair, it must be evacuated using an R-134a refrigerant recovery/recycling/charging station. If the system has been open for several days, replace the receiver/dryer, drain the refrigerant oil, and add fresh oil (see A/C REFRIGERANT OIL REPLACEMENT  ). Then evacuate the system for several hours before charging it.
  2. Connect an R-134a refrigerant recovery/recycling/charging station (A) to the high-pressure service port (B) and the low-pressure service port (C), as shown, following the equipment manufacturer's instructions. Recover the refrigerant, if any, from the A/C system (see REFRIGERANT RECOVERY  ).
    Fig 1: Connecting R-134A Refrigerant Recovery/Recycling/Charging Station To High-Pressure Service Port And Low-Pressure Service Port
    G06680565Courtesy of AMERICAN HONDA MOTOR CO., INC.
  3. Evacuate the system. The vacuum pump should run for a minimum of 45 minutes to eliminate all moisture from the system. When the suction gauge reads -93.3 kPa (-700 mmHg, -27.6 inHg) for at least 45 minutes, close all valves, and turn off the vacuum pump.
  4. If the suction gauge does not reach approximately -93.3 kPa (-700 mmHg, -27.6 inHg) in 15 minutes, there is probably a leak in the system. Partially charge the system, and check for leaks (see REFRIGERANT LEAK CHECK  ).
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