1. Shut off the unit.
2. Connect the vacuum pump to the center connection of the gauge manifold, and the gauge manifold to the high side and low side of the compressor through piercing (or any access) valves (see fig. 84).
3. Run the vacuum pump until you get a vacuum reading of about thirty inches (thirty inches below the zero) on the compound gauge. It is a good practice to heat the system by using an electric heater or heat lamp(s) and blower fans as the system is being evacuated.
4. Shut off all valves and the vacuum pump and leave everything as it is for ten minutes.
5. If at the end of this period the gauges show a pressure rise, either there is moisture in the system, or the compressor has an internal leak, or there is a leak in the system (or in the valves on the manifold gauge) that must be repaired before proceeding. (See “Repairing a Leak.”)
6. Close the valves on the suction and discharge lines and disconnect the vacuum pump from the system and connect the middle hose on the manifold gauge to a refrigerant cylinder. Connect the blue hose on the compound gauge to the suction line (see fig. 82), start the compressor, and charge the unit until the high-pressure gauge reads about 75 psi.
7. Run a leak detector over the joints and the valves. If no leak is found, complete the charging procedure. Otherwise, seal the leak and do steps 1 through 4 again.

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