Using Vacuum Pump

Vacuum pumps suitable for removing air and moisture from A/C systems are commercially available. The specification for system pump down in this case is 28 - 29 1/2 inches vacuum. 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 5000 feet elevation, only 23 - 24 1/2 inches vacuum can be attained. 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 cap from vacuum hose connector. Install center hose from gauge manifold to vacuum pump connector. Place high and low service valves (if used) in "middle" position. Open high and low side gauge manifold hand valves.
2. Operate vacuum pump a minimum of 30 minutes for air and moisture removal. Watch compound gauge to ensure system pumps down into a vacuum. System will reach 28 - 29 1/2 inches of vacuum in a maximum of five minutes. If system does not pump down, check all connections and leak test if necessary.
3. Close gauge manifold hand valves and shut off vacuum pump.
4. Check system's ability to hold vacuum.

Watch compound gauge to ensure gauge does not rise at a rate faster than one inch of vacuum every 4 - 5 minutes. If compound gauge rises at too rapid a rate, install partial charge and leak test, then recover refrigerant as described under Discharging System.
1. If system holds vacuum, charge system with refrigerant.