What is an HVAC: Everything You Need to Know

HVAC stands for heating, ventilation, and air conditioning.

In some cases, it also includes a refrigerant, so it is called HVACR.In a nutshell, HVAC is climate control in confined spaces. It is a system for the movement of air indoors and outdoors. This is what makes you comfortable in a room. In the summer, it keeps you cool. Meanwhile, in the winter, it keeps you warm.

Nonetheless, HVAC is more than just heating and cooling. This is the same system that is responsible for improving air quality. It maintains the proper humidity levels while ensuring the health of everyone in the room.

In this article, we’ll talk more about HVAC, including how the system works, reading temperature gauges, and measuring refrigerant pressure, among other things.

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How Does HVAC Work?

The best way to understand the fundamentals of an HVAC’s function is to examine its different components. Below, we’ll talk about the different parts and what they do.

1.    Air Return

This is the ventilation’s starting point. It sucks the air, channeling it towards the other parts of the system. Dirt and debris can get through the return, which will negatively impact the performance of the HVAC.

2.    Filter

It is the second part at which the air passes through before performing its desired function in a room. The filters need regular replacements to ensure the best in terms of air quality. As particles accumulate, the quality of the air it blows suffers.

3.    Exhaust

The main function of this component is to expel the exhaust that the system creates. It works as the relief fan.

4.    Ducts

Before hot or cool air is blown into a room, it needs a channel to pass through. This is what the ducts are made for. Regular cleaning, which should be done every two to three years, is essential to keep the air quality at its peak.

5.    Electricals

As the name implies, these are the parts of the HVAC that are responsible for the electronics. They are sources of ignition, so proper maintenance is necessary to minimize the risks.

6.    Outdoor Unit

When someone mentions HVAC, this is the component that most people picture. One of its main parts is the fan, which generates the necessary airflow. It must be free from debris and other things that the fan can suck, obstructing the functions.

7.    Compressor

This is another component that you will find in an outdoor unit. It converts refrigerant, sending it through the coils. It is also the part that creates the energy and sends the refrigerant throughout the system.

8.    Coil

Another part you will find in the outdoor unit cools the air that passes through it. It can be prone to freezing and other problems that can compromise the entire system.

9.    Blower

It draws warm air in the main section of the HVAC. Air must move efficiently through the blower, which makes the system more durable.

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Reading Gauges

Working with an HVAC is a complicated process, especially if you are a beginner. One of the first things that you will need to know is how to read gauges.

An HVAC gauge reads gas and liquid pressure. Also called a manifold gauge, it reads vacuum pressure. It is the most crucial equipment for any HVAC-related task.

One of the first things that you must know is color-coding. The specific color of the gauge will dictate its function:

  • Blue: This is for reading low pressure. The reading will be a measurement from zero to 350 PSI, depending on the model. This should be connected to the blue hose. It also has a vacuum reading, which is indicated as inches of mercury, which has a green section in the gauge.
  • Red: This is for reading high pressure. The reading has a maximum of 800 PSI. It must connect to the red hose.

Aside from the color, gauges are also different in terms of the type of display. The most common is an analog gauge, which has a needle that points to the exact pressure. It is prone to errors but user-friendly. On the other hand, a digital gauge has an electronic display. It is known for offering a higher level of accuracy.

A Step-by-Step Guide in Reading HVAC Gauges

  1. Connect the red hose to the red gauge. Make sure that you are using a code-authorized hose, which will tolerate high pressure.
  2. Once the red gauge has been connected, do the same with the blue gauge. Connect the system’s high-pressure side to the red hose and red gauge. It improves vacuum pressure flow.
  3. In the center of the manifold set-up, attach a waste hose or vent hose.
  4. The next part that you have to connect is the micron meter. If there are other ports,connect the necessary gauges.
  1. Once everything is ready, read the final measurements on the face of the gauge.

Converting to Saturated Temperature

First, you are probably concerned about what a saturated temperature is. In layman’s terms, this is the boiling point. This is the temperature at which the liquid will be boiling before it reaches the vapor stage.

As an HVAC technician, one of the most important tools of the trade is a Pressure-Temperature or PT chart. You can find it online, or you can also have a physical copy. This is an essential tool for the diagnosis of refrigerant problems.

However, before using a PT chart, note that it is useful only when the refrigerant has a mix of vapor and liquid pressure. You can use the measurements in the receiver, condenser, and evaporator.

When you have a PT chart, the conversion is automatic. No need to go through a complicated process or use an online calculator. All that you need to do is to take the pressure using the correct gauge. After which, compare this against the chart, and you will immediately findthe saturated temperature.

More so, you will find many modern gauges that will automatically show the conversion. The gauge’s face will display both the pressure and saturated temperature, making life easier for the technicians.

Measuring Refrigerant Charge

Another important task that novice technicians must learn is how to measure a refrigerant charge. A refrigerant is a crucial component for an HVAC system to work correctly. When it has a low charge, it won’t produce cool air. Therefore, you will need to measure the refrigerant charge at some point.

The easiest way to measure refrigerant charge is to use a pressure gauge. The result is almost instantaneous, but this isn’talways the best. While it is accurate, there are some problems. For instance, you can lose the refrigerant or contaminate the system with air and moisture. The caps and cores can also end up having leaks.

Most experienced technicians will have the initial diagnosis using only their senses. This means that they do not depend on complicated tools. Instead, they base the measurement of the refrigerant charge through keen observation. They look for oil spots, dirt accumulation, and abnormal noise, among other potential problems.

Knowing Target Subcooling

Inexperienced technicians have a lot of technical concepts to learn, and that includes the target subcooling. In most instances, you will find this written in the exterior unit of the HVAC system. Basically, subcooling is lowering the temperature of the refrigerant in the coil. Determining the target subcooling is necessary to ensure optimal performance.

To compute for the subcooling manually, all you need to do is subtract the actual line temperature from the saturated temperature. Meanwhile, depending on the subcooling, you can determine the actions that must be undertaken:

  • Add refrigerant when the actual subcooling is less than the target subcooling.
  • Recover refrigerant when the actual subcooling is greater than the target subcooling.
  • Correct refrigerant level when the actual subcooling has a difference of more or less than 3 degrees Fahrenheit compared to the target subcooling.

If the rating plate of the HVAC system does not identify the target subcooling, the safest assumption is that it is 11 degrees Fahrenheit.

Understanding Superheat

The superheat method is another important concept that new technicians must learn. In a nutshell, superheat happens when gas heats more than the boiling point in its liquid form. It is computed as the difference between a substance’s saturation temperature and the temperature of the gas. You will need the right tools to get an accurate measurement of the superheat. (we have written a guide for choosing the best dual fuel generators)

It is important in HVAC because this is what ensures that the liquid refrigerant is boiling before it exits the evaporator and enters the compressor. Otherwise, even the slightest liquid that gets in the compressor can cause significant damage, paralyzing the operation of the HVAC.

Types of a Refrigerant in an HVAC

A refrigerant is a crucial chemical in the functioning of an air conditioning system. From providing cool air to the absorption of environmental heat, it serves many purposes. For novice technicians, one of the first things to learn is the different types of refrigerants. They are not interchangeable, so using the wrong one can damage HVAC.

Measurements of the refrigerants area are easy with the right gauge. Depending on the type of gauge that you have, the face will have several measurements. Simultaneously, it will show the reading of the refrigerant that you have.


Also called freon, it is a common option for central air conditioning systems. However, it has been associated with negative environmental effects, including ozone depletion. It is no longer the default choice today since laws have banned its use.


Also called Puron, this is one of the available replacements for R-22. It does not contain chlorine, which makes it less toxic to the environment. Despite such, it has the same cooling benefits that you will find in R-22. It is also a popular choice because of its energy efficiency, increased comfort, and improved air quality.


This is another safe alternative to R-22. The use of this refrigerant requires a temperature range of -45 to 15 degrees Celsius or -49 to 59 degrees Fahrenheit. Because of the wide temperature range, it is common in commercial and industrial applications. It does not rapidly react to water and air, making it safe for many applications.

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The Most Common HVAC Problems

It is also crucial to know the different problems, and more importantly, the ideal solutions.

1.    Thermostat is Not Working

When the HVAC is problematic, one of the first parts you need to look at is the thermostat.A simple solution is to check the setting, making sure it is correct. The battery can also be anissue.

2.    Loud Noises

It is common for HVAC systems to have noise, but they should not be too loud. When the sound appears excessive and annoying, the blower motor and inducer motor are potential issues. There may also be some loose parts or worn belts.

3.    Water Leaks

Condensation is a natural result of the functioning of HVAC. Without proper drainage, water will leak. So, the first thing to repair is the drain. Checking for clogs and cracks in the pipe is also a must. The evaporator drain and heat exchange can also be the problem.

4.    Tripped Breakers

A system blockage is a common reason why the breaker trips or the fuse blows. This can also be due to a dirty air filter. The latter causes the blower to work harder, which might overwork the system and damage the breakers.

5.    Dirty Filter

One of the most obvious problems in an HVAC is the accumulation of dirt and dust on the filter. It negatively impacts indoor air quality. It also minimizes efficiency as it makes it harder for the system to run. Cleaning the filter is a must. Depending on the filter you use, you may need to change it frequently to maintain optimal airflow.

Wrapping Up

HVAC systems appear simple in theory, especially if you are the one enjoying their comfortable cooling and heating. However, it is complicated for technicians to understand, especially newbies. From subcooling to superheat, reading gauges, to understanding the types of refrigerants, technicians must have the proper knowledge about HVAC to perform an exceptional job.

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