The left hand Gauge is the low-side gauge and it is blue.

The Right hand Gauge is the High-Side gauge and it is red

The low-side port is directly under the low-side gauge , the hose is also blue

The high-side port is directly under the high-side gauge , again the hose is also red .

The centre port,or ( charge/evacuation port) is a common port between the low and high-side ports, coordinated with a yellow hose. This port is used for either, charging the refigeration system or for evacuating the refrigeration system.

The low-side valve is located to the left of the low-side gauge.

The high-side valve is located to the right of the high-side guage.

This gauge is used to measure low-side pressure and temperature, the two are directly related. to each other

Note: The low-side valve is front seated or turned all the way clockwise in order to perform this function. ( Measuring temperature and pressure)

This gauge is used to measure discharge or high-side pressure and temperature, which are inter-related to each other

Note: The valve is front seated or turned all the way clockwise in order to perform this function.

Centre Port:

You may charge vapour refrigerant , by turning the handle counter-clockwise at the low-side, while leaving the high-side valve closed

If you are evacuating or removing unwanted air, vapour, and moisture, simply open the low-side valve by turning the handle counter-clockwise.

To charge or evacuate the high side follow the same procedure, turning the high-side valve counter-clockwise.

Some refrigerants must always be charged as a liquid ( Azeotropic gases )R 134A isn't one of them. The Refrigerant Cylinder must be standing in a "normal" upright position to charge R134A , as a vapour.

Always open the high and low-side valves when pumping down or evacuating a system.

Note: Vacuum / Evacuate a refrigeration system with an evacuation pump for at least 20 minutes. After evacuating close the valves, now you should have a high vacuum registered on your gauges 20 to 30 hg. , if not you may have a leak.

If you rapidly or slowly loose a vacuum, check for leaks.

If no leaks, the system you have evacuated should maintain a deep vacuum.

Some refrigerants require special gauges due to their properties , R134A is one them.

Although 134A may be charged as a vapour or liquid , many refrigerants must be charged as a liquid. Generally charge R 134A as a gass

Azeotropic gases must be charged as a liquid.