Evacuation

Vacuum pumps suitable for removing air and moisture from A/C systems are commercially available. A specification for system pump down used here is 28-29 1/2 inches vacuum. This reading can be attained at or near sea level only. For each 1000 feet of altitude this operation is performed, the reading will be 1 inch vacuum higher. For example, at 5000 feet elevation, only 23-24 1/2 inches of vacuum can be obtained. The system must be completely discharged 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 into system, remove cap from vacuum hose connector. Install center hose from gauge manifold to vacuum pump connector. Midposition high and low side compressor service valve (if used). 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 see that system pumps down into a vacuum. System will reach 28-29 1/2 inches Hg vacuum in a maximum of 5 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 ability of system to hold vacuum. Watch compound gauge to see that gauge does not rise at a faster rate than 1 inch vacuum every 4 or 5 minutes. If compound gauge rises at too rapid a rate, install partial charge and leak test. Then discharge system as outlined above.
5. If system holds vacuum, charge system with refrigerant.