Auto A/C Terms - Glossary
Manifold Gauges - Presure Gauges

The most basic tools required to test and service any automotive A/C system are manifold gauges. They are a testing assembly consisting of a high pressure (side) gauge which will usually show pressures up to 400-500 psi, a low side gauge which is typically a compound gauge, and sometimes include an auxiliary gauge ( optional) which is another low side gauge used to test pressures across evaporator pressure regulator valves.

The manifold to which the gauges are attached include control valves that allow the user to direct the flow of refrigerant or vacuum from the center (yellow) hose to either the high or low side, or both at the same time.

Also required are manifold hoses which connect the manifold to the A/C system. Manifold hoses or charge hoses are typically available in various lengths ranging from 3 - 8 feet, however you should use caution when using long hoses. Remember, the charge hoses or manifold hoses will hold refrigerant. That in itself is not a problem. But when working on A/C systems that require a very small charge (1 or 1-1/2 pounds), understand that the long charge hoses can hold up to 2 or 3 ounces of refrigerant each. That amount of refrigerant could seriously effect the total charge level of the A/C system. This is typically not a problem when the gauges are being used constantly, because refrigerant remains in the hose at all times (the couplers do not allow the refrigerant in the hose to escape). However when gauge sets are only being used occasionally, care should be taken that if the hoses do not maintain a charge of refrigerant, the charge is adjusted to compensate for the amount of refrigerant that will be left in the hoses.

On today’s R-134a systems, couplers will also be required in order to complete the connection of the hose to the system’s charge ports. R-134a charge ports use what is commonly called ‘quick connect’ couplers. They use a spring loaded retaining ring to hold the coupler in place. The coupler also includes a valve core depressor so that it depresses the valve and provides access to the pressurized refrigerant in the A/C system.