HVAC Theory

HVAC  Theory

Thermoelectric Refrigeration: A refrigerator mechanism which depends on the Peletier effect. Direct current flowing through and electrical junction between dissimilar metals that provides heating or a cooling effect depending on direction of the flow of current. This is yet another HVAC Theory or Theory of HVAC for you to ponder while wondering about HVAC Training or Careers in HVAC.

Moving on to HVAC Theories

Your HVAC Training has many theories coupled within your HVAC Training that you will have to have a practical competency in. Each area of expertise in your job will deal with these theories. Let s look at a few of the theories to give you a better understanding.


- Wiring Series and Parallel Circuits

- Wiring Series-Parallel Circuits

- Single Pole and single throw switch circuits

- Using proper tools, like, voltmeters, ammeter and VOM and OHM Meters.

Electrical Controls and Logic

-Low voltage wiring (ie: thermostats)

-High and low pressure control switches

-Thermostatic overloads

-Relays and switches





-Vapor Compression


-High pressure vs. low pressure

-Air and non condensable, Using nitrogen

-Creating and maintaining vacuum, Evacuating


-Refrigerant recovery

-Hermetically sealed units

-Proper system charging procedures

-Terminology; Superheat, Liquid flood back, sub-cooling, metering

-Refrigerants, R-22, R-12, R-410A etc


Heat Pumps

-Theory of Operation

-Scroll and reciprocating compressors

-Auxiliary heat functions and operation



-Electrical components

Oil Heat

-Operation Sequence



-Safety switches

-CO2 Identification

-Heat anticipators

Gas Heat

-Pilot ignition

-Thermo Couple


-High limit switches

-Combustion Blower Motors

-Correct Polarity

-Gas and CO2 Detection

HVAC Training has many different aspects with a knowledge base that is ever changing as it keeps up with the introduction of new technology. Of course these theories may seem a little overwhelming however, once the basic knowledge is applied they all seem to flow together and some are more stressed than others. Each mastery of the different theories will produce more of a knowledge base for you as a technician to rely on.

Theory Sample

HVAC TheoriesEach area that is involved in the HVAC or refrigeration process has a theory. There is no one set guide for just HVAC other then the fact that all different areas combine to establish one goal. Let’s look at theory and develop a better understanding.

Our theory will be Vapors or better known as the Refrigeration Cycle. The cycle is composed of the following: Evaporation and Condensation however, many more key items and terms go along or are outlined during the cycle. Terms like: Latent Heat, Specific Heat, Liquid Line, Low Pressure, High Pressure and so on. A major term used in the industry is British Thermal Unit or BTU. I’m sure most have heard this term at some point or another.

BTU (British Thermal Unit)

The Btu is the amount of heat required to raise the temperature of 1 pound of water, 1 degree Fahrenheit. So therefore if you wanted to raise the temperature of 20lbs of water 1 degree you would essentially use 20 Btu’s to do such.

Some key terms when reviewing or studying HVAC Theory can be used and are used for the many different applications in the HVAC field. Although these terms can be used in many different applications they always have the same outcome.

-Relative Humidity





- Heat







-Saturated Vapor

In the field of HVAC , there are many abbreviations and symbols. These are symbolic of not only in the field of study when studying the different HVAC Theories but during the application of knowledge process whether it’s in sales, maintenance or operation. You should have a somewhat familiarity with these abbreviations and symbols to help you better understand the theory as a standalone or as a discipline throughout the entire area of HVAC Theories:

F= Degrees Fahrenheit

C= Degrees Centigrade

F/A= Degrees Fahrenheit/Absolute

C/A= Degrees Centigrade/Absolute

R°= Degrees Rankin

K°= Degrees Kelvin

P= pounds

psi= pounds per square inch

i= Inches

f= foot or feet

si= square inch

sf= square foot or feet

r= radius of a circle

pcf= pounds per cubic foot

Hg= Inches of mercury

Hp= horsepower

W= watts

Ft.lb.= foot-pounds

Ton= ton of refrigeration effect

lb/cft.= pounds per cubic foot

psig= pounds per square inch gauge

psia= pounds per square inch absolute


When studying HVAC Theories keep the following in mind:

-What does absolute pressure and mercury of vacuum mean and how to they interact?

-The difference of a vapor and liquid and how they moved, condensed or vaporized.

-How Btu’s are used in order to size a AC unit or refrigeration.

-Refrigerant Pressures and temperature relationships

-Absorption of Heat

-What determines the temperature of refrigerants at which they will vaporize?

-The different types of heat transfers, convection, conduction and radiation

-Converting temperatures from C to F and vice versa

On occasion I will be updating HVAC-Trainingclass with different terms that you will find perhaps useful in not only your educational search but your career search as well. Careers in HVAC begin with HVAC Training and the HVAC Theory that is involved.