Using Vacuum Pump

Vacuum pumps suitable for removing air and moisture from A/C systems are commercially available. The pump should be capable of drawing the system down to 28 to 29 1/2 inches Hg at sea level. For each 1000 foot increase in altitude, this specification should be decreased by 1 inch Hg. As an example, at 5000 feet elevation, only 23 to 24 1/2 inches Hg can be obtained.
1. Connect suitable gauge manifold and discharge system as outlined previously. System must be completely discharged prior to evacuation. If pressurized refrigerant is allowed to enter vacuum pump, pump will be damaged.
2. Connect hose from gauge manifold center port to vacuum pump inlet, then position high and low side compressor service valves in the middle, if applicable.
3. Fully open both gauge manifold hand valves.
4. Operate vacuum pump while observing low side compound gauge. If system does not "pump-down" to 28 to 29 1/2 inches Hg (at sea level) within approximately 5 minutes, recheck connections and leak test system.
5. Continue to operate vacuum pump for 15-30 minutes, longer if system was open for an extended period of time, then close both manifold valves and stop pump.
6. Check ability of system to hold vacuum. Watch low side compound gauge and ensure that reading does not rise at a rate faster than 1 inch Hg every 4-5 minutes.
7. If system fails to hold vacuum, recheck fittings and connections, and leak test system.
8. If system holds vacuum, charge system with refrigerant.