How Air Conditioning Gauges Work for Beginners

Bryan shows how air conditioning gauges work. This is HVAC training for beginners to the HVAC/R trade, not homeowners or those who aren’t properly certified. We cover the basics of how an air conditioning and refrigeration manifold works and how we use it in the field.

The gauges are on top of the manifold; the manifold refers to the actual assembly with the gauges, hoses, valves, and sometimes even a sight glass. We use the gauges to help us determine saturation temperatures and pressures for various refrigerant types; there are low-pressure and high-pressure gauges. We have to calibrate the gauges to atmospheric pressure (hence PSIG: pounds per square inch gauge).

The hoses can be screwed onto parks to keep them from being contaminated when the manifold is not in use. However, it’s best to calibrate your gauges with the hoses open to the atmosphere. The manifold has a high side (usually red) and a low side (usually blue). The center port (usually yellow) is for charging and recovery.

The handles have nothing to do with the gauges themselves; handles merely open valves that allow communication between the center port and the high or low side (depending on which handle you turn). In most cases, you will only open one handle at a time (unless you’re feeding refrigerant from the liquid side to the suction side or vice versa). Don’t over-tighten the handles!

Normally, you will just use the center hose and one side depending on if you’re charging the system (middle to low side) or recovering from it (high side to middle).

Manifold hoses may also have core depressors, which depress the Schrader cores inside service valves and allow the flow of refrigerant. Some gauges also have a sight glass, which allows you to watch the refrigerant flow when you’re charging or recovering refrigerant.

There may also be a hook at the top of your gauge manifold, which allows you to hang the manifold from your equipment. (Make sure you don’t poke the hook into your condenser coil!)

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