How to Use HVAC Manifold Gauges | 3 Simple Ways

Any heating, ventilation, air conditioning, and refrigeration service technician require an HVAC charging manifold, or gauges, in their job. 

The equipment is used for reading the pressure of gases and liquids, such as refrigerants in an air conditioning system.

Technicians also use the gauges to check the vacuum pressure when charging or pressure testing a cooling unit.  

If you don’t know how to use HVAC manifold gauges, you are at the right place. Read along to learn more. 

What you will Need to Use HVAC Manifold Gauges

To service an AC unit or check if every device in an HVAC system is working correctly, you will need a set of pressure gauges with these main components: 

  1. Gauge manifold

This component acts as the point of attachment for the three-chamber devices, namely: low-pressure chamber (left), utility chamber (middle), and high-pressure chamber (right).

The low-pressure side of the device connects to the unit’s low-pressure port via its (blue) gauge hose.

The (red) high-pressure gauge hose attached to the high side connects to the corresponding high side of the unit under servicing.

The utility chamber connects to any external source (refrigerant cylinder, vacuum pump, or recovery unit) via the yellow hose.

  1. Readout gauges

Your HVAC manifold will have two readout gauges. These are for displaying the vacuum or pressure level in the AC unit

Low-side gauges are blue, while the high-pressure side is color-coded red. For most HVAC gauges, the low side reading often ranges from 0 to 99.9 psi (350 in this example), while the red gauge goes up to 999 psi (800 in our example). 

How to Use HVAC Manifold Gauges

You need specific knowledge on using these gauges for tasks such as vacuuming, testing, adding refrigerants, and recovering refrigerants from a cooling unit. Let us look at some of these tasks. 

Step-by-Step Instructions

1. Reading vacuum pressure already in a system.

  • This is one of the basic tasks of the HVAC manifold gauge. 
  • To get the pressure readings, attach the red hose to the HVAC system’s high-pressure line. The hose will connect the high-pressure gauge to the corresponding high-pressure line of the cooling unit.
  • Next, attach the blue hose to the low-pressure line of the cooling unit. As you should already know, the blue hose connects the low-side gauge to the AC system’s low-pressure line. 
  • You will not be using the yellow hose (and utility chamber) when getting pressure readings.
  • Whether the AC system is off or running, the pressure readings should instantly appear on the gauges as soon as you attach them. The pin on each gauge will point at the corresponding pressure reading on the outermost psi scale. 
  • It is important to use the appropriate hose on the right side because they are designed to withstand pressure levels differently. 
  • Usually, the high-pressure port is of a different size and thread than the low-pressure port to avoid the likelihood of random inaccurate hookups.
  • Note: Before attaching the gauges, always ensure that both the right and left valves are closed. 
  • If you connect the hoses while either or both the high side and low side valves are open, refrigerant could leak out through the central valve. 
    • The majority of the time, when you add refrigerant to an AC system, you will often add it through the low side. 
    • Start by connecting the yellow center hose to the refrigerant cylinder and the blue hose to the cooling unit. 
    • Once this is done, open the valve on the left, low-pressure side just a tiny bit, and then slowly let the refrigerant flow into the system as you monitor the gauge.
    • If the system is off and you need to charge it from a zero starting point, you can charge a potion or the refrigerant through the high-pressure side. 
    • In this case, the yellow hose will still go to the refrigerant bottle, but you’ll use the red hose instead. So, connect the red hose to the unit’s high-pressure line and slightly open the corresponding valve.
    • The red valve will control how much goes into the unit and turn off when the correct amount has been added.

    3. Discharging an AC system or vent Freon 

    • To recover refrigerant from a cooling unit, you’ll need to connect the yellow hose in the middle to a refrigerant recovery container.
    • For a system that was overcharged, connect the red hose to the high side port of the system. Ensure you do this while the AC system is running.
    • Once you have connected the yellow hose to the recovery container and the red hose to the high side of the unit, open the valve to start dumping out the refrigerant.

    Other Posts: When to replace your HVAC System

    Final Thoughts on How to Use HVAC Manifold Gauges

    The list of uses of HVAC manifold gauges is as long as the number of jobs a technician does. For example, you may routinely need to pump down a mini-split HVAC system to carry out general repairs or replace the line set.

    You may also want to move an Air Conditioning unit from time to time. Whatever the case, you must have specific knowledge on how to use HVAC manifold gauges. 

    In any case, the instrument has been color-coded with blue and red hoses corresponding to the blue and red gauges. 

    Further, you have this guide to walk you through the basics of using the manifold gauges. We will be delighted to hear your thoughts in the comments section. 

    If you experience any technicality and need a professional, use this manual to hire a technical HVAC contractor

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Jesse Pinkman is a passionate HVAC professional writer who grew up repairing any home appliance on which he could lay his hands. He is responsible for ensuring that every article we publish is SPOT ON. When he's not in the office, he enjoys hiking, watching football, and spending time with his family.