A/C Evac and Refrigerant Refill Procedure

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Tools Needed:

1. R134a A/C Manifold Gauge Set (The gauge set sold by Harbor Freight is recommended. This set comes with all necessay hoses and connectors. Most sets do not inculde all connectors.)

2. R134a Vacuum Pump (Available at Harbor Freight for $10-$15)

3. Air Compressor (Capable of 4.2 CFM @90 psi.)

4. R134a A/C Can Tap

5. R134a Refrigerant

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Evac and Refill Procedure:

1. Close both valves on each of the two gauges.

2. Connect the gauges to the high and low port on the ac system.

3. Connect the inlet/feed hose of the ac manifold gauge set to the vacuum pump

4. Set the compressor to a minimum of 90psi.

5. Start the compressor

6. Connect the compressor output/supply hose to the vacuum pump.

7. Open the valves at the ports, and the valves at the manifold.

    • It should take between 2-5 minutes to create and maintain a vacuum at 28 inches or more of Hg.
    • This high vacuum is necessary to remove all traces of moisture that may have gotten into the system.

8. Leave the compressor/vacuum pump running 45-minutes to 1 hour minimum. The longer it runs the better.

9. At the end of the evacuating/vacuuming period, shut both the high and low port valves at the manifold. Leave valves at the ports open so you can observe the state of the vacuum inside of the ac system.

10. Now observe the gauges to watch for loss of vacuum for a minimum of 1 hour. Gauges may drop very slightly when valves at the manifold are closed and the vacuum source is cut-off from the ac system.

11. You can disconnect the vacuum pump from the compressor at this point, so the compressor can shut off.

    • If no loss of vacuum for at least 1 hour, ac system is tight and ready for filling with refrigerant.

12. When ending vacuum observation period, and preparing to fill with refrigerant , first close both high and low port valves at the ports.

13. Connect the refrigerant can to the can tap. Connect the hose to the can tap, and to the ac manifold.

14. Pierce the seal on the can, then loosen the fill hose at the ac manifold. Open the valve at the can tap, and bleed the air from the hose by allowing a small leak at the maifold to fill hose connection, when refrigerant is coming out, tighten the connection to seal.

15. Reconnect the hoses to high and low ports if you disconnected them.

16. Initially you can start filling the system with R134a with the engine off. Open both the low side and high side ports to fill the system, BUT YOU MUST CLOSE THE HIGH SIDE VALVE WHEN THE ENGINE IS RUNNING.

17. DO NOT FLIP THE CAN OF REFRIGERANT UPSIDE DOWN WHEN FILLING. That will cause liquid refrigerant to be forced out of the can, through the manifold gauge set and into the low pressure system, where it will immediately expand, and blow the pressure up above design specs. The low pressure system and the gauge set are not designed to handle liquid refrigerant.

18. You can stick the refrigerant can in a pail of hot water to heat it, as it will freeze as the refrigerant transfers to the ac system. Otherwise, the transfer of refrigerant will slow. When the can has returned to room temperature, it is empty. Most probably, you will not get much more than 1 or 1.5 cans to go into the car without running the engine. REMEMBER, IF YOU ARE FILLING FROM THE HIGH SIDE VALVE, YOU MUST CLOSE IT BEFORE YOU START THE ENGINE AND RUN THE AC SYSTEM.

19. If the compressor clutch will not engage after filling with 1 to 1.5 cans of refrigerant, try shorting the low pressure switch with a paper clip while the electrical connector is still plugged in. If you get to the point where the ac manifold gauge set indicates the pressure is steady above 15-20psi on the low side, then the low pressure switch is probably defective. THIS IS A COMMON FAILURE. You can replace it by unscrewing it without losing the refrigerant charge, because there is a schrader valve (tire type valve) located below the switch which will keep the refrigerant from leaking out.

20. Don't be surprised if the system takes more than the 32oz listed on the label under the hood. When filling from empty, I have found that most systems take more than the label says. Just watch the pressure on the high and low sides to make sure that you don't overfill.

      • Some people say to charge only until the output air becomes cool. I say add refrigerant until the system pressure is at spec on both sides of the system.

Overcharging is as bad as undercharging. Stop adding refrigerant when the pressure are correct. Don't dump in the whole can when it isn't necessary. And don't stop adding until the system is full.***

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