Vacuum Pump

Vacuum pumps suitable for removing air and moisture from A/C systems are commercially available. The system pump down specification used as a reference point is 28-291/2 inches Hg vacuum. However, this reading can be attained at or near sea level only. For each 1000 feet of altitude at which this operation is performed, the reading will be one inch of vacuum higher. For example, at an elevation of 5000 feet, only 23-24 1/2 inches Hg vacuum can be obtained. The system refrigerant must be completely recovered before it can be evacuated. Damage to the vacuum pump will result if pressurized refrigerant is allowed to enter.
1. Connect vacuum pump to gauge manifold. With gauges connected to system, remove vacuum hose connector cap and connect gauge manifold center hose to vacuum pump connector. Place high and low side compressor service valve, if used, in middle position and open high and low side gauge manifold hand valves.
2. Operate vacuum pump for at least 30 minutes to remove air and moisture. Observe compound gauge to ensure system pumps down into vacuum. System should reach 28-291/2 inches Hg vacuum within five minutes. If system does not pump down, inspect all connections and leak test if necessary.
3. Close gauge manifold hand valves and shut off vacuum pump.
4. Evaluate system's ability to hold vacuum pressure. Observe compound gauge and ensure needle does not rise at a rate exceeding one inch Hg vacuum every four or five minutes. If gauge rises at too rapid a rate, supply partial charge and leak test, then recover refrigerant as described under "Discharging System".
5. If system holds vacuum, charge with refrigerant.