How to Hook Up & Read HVAC Gauges

Gauges are used to read the pressure of various liquids and gases in a cooling system, as well as vacuum pressure when you are pressure testing or charging the device. There are a number of different ports on the HVAC gauge set, also known as a manifold, and the main difference in the types of manifolds is the number of ports that you have available to attach accessories to, as well as the pressure that the gauge set can withstand, which is important when working with different refrigerants.

1. Connect the high pressure side of the cooling line to the red port on the gauge. The red port and red gauge are always the high pressure gauges. You will want to attach a code-approved red hose, which is made to withstand high pressure, using the flare fittings that are included with it, to the high pressure port on the cooling unit. The high pressure port is typically of a different size and thread pitch than the low pressure side in order to avoid the potential for accidental incorrect hookups.

2. Connect the low pressure side to the blue port on the gauge. The low pressure side will be connected with a blue low pressure hose to the blue pressure gauge and the low pressure side of the cooling unit. This will allow for the proper flow of vacuum pressure or a micron meter in order to determine the vacuum pressure in the system already.

3. Attach a waste hose or vent hose to the center of the manifold set up. If you are going to discharge a unit, or if you are going to vent freon by attaching the unit, you will need to attach the larger black low pressure hose to the center port of the manifold. By doing so, you will be able to attach a refrigerant recovery bottle to the manifold set to avoid violating federal law regarding the release of refrigerant into the atmosphere.

4. Attach micron meters or other gauges to the additional ports. The additional ports on the manifold can be used to attach micron (vacuum pressure) gauges, or even a vacuum pump, in order to perform the proper services to the cooling system as required for the repair that you are making.