Evacuating the AC System – External Pneumatic Vacuum Pump

A pneumatic vacuum pump is a very economical choice for pulling a vacuum on an AC system. This type of pump uses shop air pressure to create a vacuum device that is connected to the yellow hose on the manifold set. These tools require at least 75 psi of air pressure to operate effectively. Follow these steps to use this tool.


A pneumatic vacuum pump is a low-cost method of pulling a vacuum on the AC system. This tool uses compressed air to spin a pumping device that creates enough vacuum to be used on an AC

Evacuating the AC System with a Pneumatic Pump

1. Connect the blue hose of the manifold set to the low side service port and turn the blue knob clockwise to depress the check valve.
2. Connect the red hose of the manifold set to the high side service port and turn the red knob clockwise to depress the check valve.
3. Connect the yellow hose of the manifold set to the port on the vacuum pump by threading the connection in a clockwise rotation.


The yellow hose from the manifold set connects to the pneumatic vacuum pump threaded connector. This connection should be tightened to a snug level using a firm

4. Open the valves at the mani fold by turning the blue and red knobs counterclockwise. This lets the blue and red hoses be open to the yellow hose, which is connected to the vacuum pump.


The blue knob on the manifold set must be opened to allow the low side of the AC system to be pulled into a vacuum with the electric vacuum


The red knob on the manifold set must be opened to allow the high side of the AC system to be pulled into a vacuum with the electric vacuum

5. Connect an air hose from a good shop air source to the pneumatic vacuum pump and turn on the air supply to start the vacuum operation. Make sure the check valve is open on the vacuum pump.


The pneumatic vacuum pump must be connected to a compressed air source to power the device. When the air hose is connected to the pneumatic pump, an audible sound will begin that indicates that the pump is

6. Watch the gauges on the manifold set drop. The red gauge will drop down to 0 psi and the blue gauge will drop to below 0 psi, which will be in the vacuum part of the gauge in inches of mercury. The blue gauge should reach 20 inches of mercury within 10 minutes of operation.

7. This process should pull the low side gauge to 29 inches of mercury, which will remove any moisture from the AC system. The vacuum time should be at least 30 minutes if the system has been open to the atmosphere.


The pneumatic vacuum pump will pull the low side gauge into a tight vacuum and the high side gauge down to zero. Reducing the system pressure to this level removes the air and moisture from the AC

8. To stop the vacuum process, turn the blue and red knobs on the manifold set clockwise to block the vacuum process. The vacuum pump can now be turned off and the yellow hose can be removed. The vacuum should stay constant on the blue gauge, which shows that the system does not have any leaks. The system is now ready to be charged with refrigerant.


The blue knob on the manifold set must be closed in order to seal the vacuum in the AC


The red knob on the manifold set must be closed in order to seal the vacuum in the AC

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