Fridges and air conditioners work in similar ways. They use refrigerant to keep food fresh and air temperatures indoors bearable. Fridges rely on evaporation, or the constant compressing and depressurising of refrigerant to expel hot air outside. The same goes for air conditioners. Refrigerant collects heat inside the house, gets hot, transfers that heat outside, and cools. Of course, there’s more science to this, but both appliances are effective at what they do. That is until there’s a drop in refrigerant or coolant pressure.
In cases like these, you’ll see HVAC and refrigeration technicians use a manifold gauge. This is an instrument that measures the pressure of refrigerant in the system, assesses if there are leaks, and helps maintain the right pressure when the refrigerant or other coolant is topped up or replaced.
Manifold gauges might not be everyday household tools, but they’re the spanners and hammers of HVAC and fridge diagnosis and maintenance. As such, there are more than a few types. Gauges differ by the number of ports they have and the accessories that can be attached to these ports. There are also analogue and digital types. Both are accurate but there are pros and cons to each. Digital manifold gauges from respected brands like German instrument giant Testo offer higher accuracy, unrivalled ease of use, and speedy operation. They also work with different types of refrigerants, so are also more versatile.
Parts and How Manifold Gauges Work
Analogue or mechanical gauges have been around for decades and are what most technicians are familiar with. They consist of a central manifold with hose connections or ports below, a blue low-pressure gauge and red high-pressure on top, and side valves for regulating pressure and charging (or refilling) systems with refrigerant.
The manifold can have three or four ports. In three-port types, blue hoses connect to the (left) low-pressure port for vapour, red hoses connect to the (right) low-pressure port for liquids, and the central yellow port is used in recovery from a refrigerant bottle, checking compressor status, and maintaining proper gas flow. Four port systems use the additional port to attach devices like vacuum pumps to clear fridges or air conditioners from refrigerant that has been contaminated.
Digital manifold gauges provide all the functionality of analogue gauges but offer more precise pressure readouts. These are displayed on an easy-to-read LCD display that replaces the needles on analogue variants. A major benefit of advanced digital devices, like those from Testo, is that they can be calibrated to work with many types of refrigerants, meaning they can successfully diagnose both older and newer appliances.
Besides pressure, digital gauges have built-in thermometers (used with the appropriate clamps) to measure superheat and supercool values in real-time, or the efficiency of the HVAC system in removing heat at low and high settings. Some additionally have built-in micron meters used in the vacuuming phase to ensure there are no leaks. Added to this is the ability of data-logging when tracking repetitive issues, and recording data for future reference. All Testo manifolds are also equipped with Bluetooth connectivity to beam data to phones or tablets and offer more functionality (like pairing wireless temperature clamps) with advanced apps.
What to Look for in Manifold Gauges
If you’re an HVAC technician or someone who repairs fridges for a living, then you’ll want a manifold gauge that’s accurate, well-built, and versatile across different uses. This also means compatibility with different refrigerant types.
Analogue or Digital?
While analogue gauges are reliable and accurate, it’s up to the technician to correctly interpret data and ensure whether air conditioners and fridges are working as they should. Here there is more room for guesswork, with slight variations in readouts and compiled data leading to more errors. Digital manifold gauges are far more accurate and with the right training are easier to master, and easier to use. An added bonus is that they also save time with very fast readouts.
Go for a Robust Build
In terms of durability, both types are designed to last. Digital gauges should be IP-rated against impact, temperature extremes and water ingress so the quality of the housings is just as important as that of the ports. To ensure your equipment lasts, also look for gauges sold with matching hard-wearing carry cases. Longer warranties (3 years) or more also bring peace of mind.
Pressure Ratings
Gauges that can measure higher pressure are both more durable and more versatile. And they can provide more precise data across standard or heavy-duty systems. For digital types, go with maximum pressure ratings of 60 Bar or more.
Refrigerant Types
Since newer AC systems and fridges are moving towards more eco-friendly and efficient refrigerants, you’ll want a manifold gauge that can accurately measure pressure readouts for different types of refrigerants. Even the most inexpensive Testo gauges, for instance, have pre-installed data for over 60 of the most common commercial and industrial refrigerants and this number increases with the app.
Additional Features
Documenting findings is another key benefit of digital over analogue manifolds. This allows data to be stored or used as needed. Most digital types are also Bluetooth compatible so transferring readouts to other devices is simple.
Price
Analogue gauges are cheaper, but limited in use to a specific set of refrigerants and require more skill to be used accurately. Digital gauges are far more advanced, always precise and can save time in unwanted errors. They are somewhat dearer, but if accuracy, versatility, convenience and speed are priorities, then a quality digital manifold gauge from an established brand should be high on your shopping list.
