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Learn How to Read Digital HVAC Gauges

Every HVAC technician knows how to read digital HVAC gauges!

As a technician, you work with various heating, ventilation, air conditioning, and refrigeration equipment and appliances daily. A digital refrigerant gauge is one instrument you should never leave behind while undergoing repairs or examinations; it must be your most precious asset! You'll agree with me that you rely heavily on your digital HVAC gauges.

Don't get me wrong; gauges are quite useful and fantastic diagnostic instruments that precisely read the pressures of any refrigerating system. Without a set of gauges, you can identify or troubleshoot the condition of an HVAC/R system. But don't get too caught up in the details; as you grow more comfortable with systems and how they work, a lot of things become second nature to you.

Digital HVAC Gauges

Digital gauges are more efficient than analog gauges because they provide pressure readings in numbers, down to 1/10th of a PSI. What a feat of efficiency! You won't have to interpret the readings, which means you'll be less likely to make mistakes.

What makes digital gauges valuable is the added capabilities, such as automatic pressure to temperature calculations. Most of them have Bluetooth temp clamps for the pipes, like the latest Testo ones, or wired temp clamps, like the Fieldpiece SMAN3, which I started with.

When these temperature restraints are installed, it may do automatic Superheat and Subcool calculations once more.

How to Read Digital HVAC Gauges

Before we go any farther, let's review what to look for on a manifold. High/Discharge/Liquid refers to the system's higher pressure side, and its colour is always red.

The liquid line, also known as the discharge line or discharge pipe, is the smallest pipe leading to the compressor. The fluid line is always larger than the suction line.

Suction or low side is always the Blue side; it's the system's more down pressure side.

Let's have a look at how to interpret a refrigerant manifold.

Step 1:

Connect the red hose (red on your gauge face if it's analog) to the high-pressure component of your system. It will, once again, be the smaller of the pipes, sometimes insulated but not very often.

It is commonly done with small Schrader fittings, similar to what you'd find in a car or bicycle tire. When you screw on the hose, a section of the line presses into the Schrader, allowing refrigerant to flow into the hose and giving you a pressure reading.

Also, you can service valves at the receiver or on the compressor that need to be turned with a service tool or a socket, but the service wrench is the best option. It does not harm the stem in the same way that a crescent might. When you forget where you put the wrench, now, let's go on.

It has three places when you break it open, which is a little perplexing because you turn it clockwise.

  1. All the way clockwise, on the port side (where your manifold hose attaches in), completely shut and closed, and closed flow (the hose that links to the valve).
  2. Open the port and flow sides by turning it clockwise just a hair. It gives you a pressure reading without stopping the system or causing too much disruption.
  3. When the valve is fully turned out counterclockwise or as open as it can get, it is closed on the port side but open on the flow side. It closes the port side but leaves the flow side open, allowing the system to operate; this is how you'll find it when you first start working on it.

Step 2

It would be best to connect the blue port to the low-pressure side. Attach the blue hose to the low side pressure port like you did the red one (Schrader or service valve).

Step 3

When you first join up to the system, you'll want to purge a little, so as you screw on your hose to the Schrader connection, open your manifold to ensure that no air is caught in your hose and enters the system. The aim is to use an already purged manifold, which still has some refrigerant. It pushes the refrigerant out of the hose as the last connection to the system is made.

You should also do it on the high side. However, if you've ever attempted connecting into a high side while the system is turned on, getting it on without frostbite is good enough for me.

Step 4

Check your hoses on the manifold side and the system side, and check that nothing is loose.

Step 5

That's about it; there's no Siri or Alexa to inform you if you're doing it right or poorly. The manifold gives you information; it won't tell you all you need to know, but it will tell you what you need to know to find out what's wrong.

Reading Vacuum Gauge

When repairing a system that requires you to open it up, you should always pull a vacuum down to less than 500 microns. If the vacuum sensor is not connected to the manifold, it should never be pressured above 1-10 PSI. You also don't want to connect your vacuum pump and apply pressure to it because this will cause oil to leak from the pump's exhaust.

Close the pump and add just enough refrigerant to break the vacuum before removing your vacuum probe if you're switching from vacuum to charge. If you try to remove it from a Schrader while it's under vacuum, it'll suck air in and pollute the system the instant the vacuum probe lets go, and the Schrader closes. It's simple, but it's also unneeded and untidy.

Switching hoses from your vacuum pump to your refrigerant cylinder is also risky; one mistake flip of the valve, and you've allowed air in, forcing you to restart the vacuum.

Digital HVAC Gauges from HVAC Shop

Refrigerant gauges are essential to air conditioning equipment that can assist you in diagnosing and correcting air conditioning and stationary refrigeration devices that aren't cooling effectively.

Here at HVAC Shop, we have different digital HVAC gauges from other trusted brands like Robinair, Mastercool, Yellow Jacket, and more. Please browse through our collection today!