Auto A/C Terms - Glossary
Manifold

Typically a part of the manifold gauge set, the manifold is usually made from aluminum or brass and is used to control refrigerant flow through the charge hoses by means of hand valves or control valves.

The hand valves open and close to connect the various passageways in the manifold. Typically, when the pressure gauges are connected to an A/C system, the hand valves will be closed so that refrigerant in the system will not be lost.

As an example, in order to add refrigerant (freon) the system through the low pressure charge port, the low side hand valve would be opened to connect the passage from the center or yellow hose (where the refrigerant source is) to the low pressure hose, which would be connected to the low side charge port of the A/C system.

As for pulling vacuum on the A/C system, with a vacuum pump connected to the center (yellow) hose and both high and low side charge hoses connected to the A/C system, both hand valves would be open to connect both high and low sides of the A/C system to the vacuum pump.

Whenever using manifold gauges, always be sure that both high and low hand valves are closed before connecting them to the A/C system. Even when the hand valves are closed, the pressure gauges will provide refrigerant pressures.