6 Common Questions about AC Gauges / Freon Gauges

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Last updated: 
March 17, 2024

Manifold air conditioning gauges are employed to check on the pressure of the refrigerant. Nowadays, most refrigerant cans on the market come with an implemented gauge. However, this will only tell you what the low side pressure is. On the other hand, manifold gauge sets enable you to measure not only the low side pressure, but also the high side one. Additionally, they also let you know what the maximum vacuum level that can be maintained in the vacuuming stage is.

1. What are AC gauges / Air Conditioning Gauges?

AC Gauges - freon gaugesImplemented with a chamber design, air conditioning gauge manifolds were created to regulate the gas or pressure flows, and they comprise high pressure and compound. The three main chambers of the AC manifold gauges are:

  • right side – high pressure chamber;
  • middle side – utility chamber;
  • left side – low pressure chamber.

When an HVAC specialist wants to connect the manifold freon gauges to the AC unit, he will link the left side (low pressure) of the gauge to the low pressure side of the AC. In order to read the discharge line pressure, he will connect the high pressure of the air conditioning unit to the right side (high pressure chamber) of the gauge hose. For removing or adding refrigerant in the air conditioning units, the middle or utility chamber will be connected to the hose of the vacuum pump.

2. How does an A/C gauge work?

The mechanism behind air conditioning gauges is very simple: the opening and closing of the hand valve does all the work. The AC assemble has a needle and a small port either in the utility chamber or from the opposite side of the low pressure chamber to the high pressure one. If you want to open the hand valves for low pressure, you’ll have to rotate it counterclockwise in order to open the utility’s chamber low pressure port. In a similar manner, in order to close the utility chamber’s low pressure port you’ll have to rotate it clockwise. The same steps apply for the high pressure hand valve. For opening the AC gauge you have to rotate it counterclockwise and closing it requires a clockwise rotation.

When the low side of the air conditioning unit, also known as the suction line, is connected to the low pressure hoses, the low pressure chamber will instantly indicate the pressure, without anything having to be open. The high pressure chamber follows the same steps. If you want to remove or add refrigerant, vacuum the system or move refrigerant into the cylinder, you will need to open the port for the middle side (utility chamber). You will find the needed accessories are connected within the utility hose. For reading the temperature and the pressure within a closed system, you will need to connect your HVAC gauges to your central air conditioning unit.

3. Why use an AC gauge?

AC GaugesThere are plenty of manifold air conditioning gauges for AC repair. Nonetheless, their purpose boils down to the same principle: helping the professionals who service HVAC equipment to keep a close eye on the pressure within the units. They also enable technicians to determine when they have to remove or add refrigerant as well as determine the quality and the kind of the refrigerant that can be found within the system. A HVAC gauge meets all these criteria. The gauge is used to define the entire assembly comprising the individual gauges. 

The main function of a HVAC gauge is to accurately determine the pressure and the temperature in a closed system. Based on these readings and measurements, the technician can determine if your AC unit is performing properly or if it is in need of specific repairs. If your air conditioning unit is not cooling properly or if you feel some rooms of the house are warmer than others, a HVAC gauge will pinpoint the issue. This is not only the case for air conditioning units installed in apartments and homes, but also hospitals or food warehouses, where a stable temperature is an absolute necessity. In addition to this, an air conditioning unit that is performing at its full capacity will cut down on unnecessary expenditures such as emergency service appointments, extensive damage to essential parts and downtime.

4. What are the main parts of an AC gauge assembly?

Most HVAC gauges available on the market nowadays comprise two readout gauges that stick out from the top side of a manifold or framework that is made out of brass. There are also lines and hoses, which connect to the manifold’s base, and which are in charge of draining, checking, and supplying the pressure inside the AC unit.

  • The manifold. This part of the air conditioning unit gauge comprises three ports, two valves and three chambers: low pressure, utility and high pressure chamber, arranged to the left, middle and respectively right side. Each one of these three chamber includes a port for hose attachments. The valves that are positioned on the two sides are meant to regulate the nitrogen or refrigerant outflow and inflow whenever the air conditioning unit is in need of a system purge.
  • The readout gauges. Air conditioning gauges consist of one gauge for the low pressure chamber and another one for the high pressure chamber. In order to differentiate between them, they are color coded: red for the high pressure chamber gauge and blue for the low pressure chamber gauge.
      • The low side gauge is dubbed the compound gauge. This part of the air conditioning unit gauge is in charge with reading the positive pressure as PSIG, which translates into pounds per square inch gauge. At the same time, the negative pressure is read in inches of mercury that is also known as vacuum. These two readings are relative to standard pressure. The figures on the low side gauge, which has blue hoses, will vary from minus thirty PSIG, to plus a hundred and twenty.
      • The high side gauge is situated on the right side and has red colored hoses. In order to avoid and prevent frostbite when dealing with the high side connections, low loss fittings or a pair of special gloves are essential. While low loss fittings might not be so important on the low side, they are in charge of limiting the refrigerant released into the atmosphere. The HVAC specialist will connect this side to the air conditioning unit liquid or discharge line port.
  • The hoses. These play an essential role in any air conditioning unit gauge, which is why they have to be rated in order to manage the pressurized gasses that go through them. Bear in mind that if you want to change a correctly rated hose, which came with the air conditioning unit hose, you should steer away from hoses that have lower psi ratings. The hoses that start from the refrigerant’s tank and go to the gauge’s utility port are colored in yellow and their purpose is to add refrigerant when the AC unit needs it. A noteworthy trick to take into account is adding a valve to this hose, which allows technicians to accurately control the volume that is being fed into the system.

5. How do you calibrate the AC gauges?

AC GaugesIt is essential to calibrate the two gauges before they are put into use. In order to calibrate them, you will have to open the low valve and the high valve of the manifold after you have removed the hoses. Next up, take off the covers that protect the faces of the gauge so you can gain access to the calibration screws. Make sure to slightly tap the sides of the gauge in order to reposition the needle after you are done with your adjustment. The needle must rest on zero.

6. How do you add refrigerant?

If you are using a separate thermometer that is linked to the line through a wire and you notice the temperature reading exceeds the normal figures, you will need to add more refrigerant. The first step is to connect the yellow colored hose that goes from the utility port to the required refrigerant’s tank. Next up, you will want to slowly and steadily open the valve from the manifold’s low pressure side in order to add the appropriate refrigerant until the thermometer indicates the correct temperature. On the compressor cover, you will find a chart that will indicate the correlation between the low pressure reading of the gauge and the current temperature of the refrigerant that is passing through the line. When you see that the thermometer shows the desired temperature, you can go ahead and close up the valve of the supply tank’s refrigerant, also shutting down the blue valve from the air conditioning unit gauge. The final step is disconnecting the hoses and replacing the valves’ caps.

7.  AC Gauges Final Thoughts

If you want to avoid emergency service calls and constantly keep an eye on your air conditioning unit, HVAC Freon AC gauges will help you do just that. The process is not rocket science and it can easily be picked up by novices through a little trial and error.

Image sources: 1, 2, 3.

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