Auto A/C Terms - Glossary
Expansion Valve
Every automotive A/C system includes an expansion valve or expansion device of some sorts. The typical expansion valve, also referred to as a thermostatic expansion valve is...

Auto A/C Terms - Glossary
External Equalizer
Some conventional type expansion valves which use a capillary tube sensing device, also include an external equalizer tube. The external equalizer is actually...

Auto A/C Terms - Glossary
Fahrenheit
One of the commonly used temperature scales that measures the intensity of heat. In Fahrenheit, water freezes at 32 degrees and...

Auto A/C Terms - Glossary
Fan Clutch
Most engine driven fans on vehicles now incorporate a fan clutch. The clutch is actually a drive coupling that is filled with a viscous fluid that will...

Auto A/C Terms - Glossary
Feedback Potentiometer
The feedback potentiometer is a variable resistance device used on older automatic temperature control systems where the in car temperature could be set and the system would maintain that temperature using both air conditioned and heated air. The feedback potentiometer...

Auto A/C Terms - Glossary
Filter - In Line Filters
Auto A/C systems require filters in order to trap contamination and debris. Understand that it takes less than one tenth of a teaspoon of debris to cause serious problems in any A/C system. That debris is a result of ...

Auto A/C Terms - Glossary
Flush - Flushing A/C Systems
Flushing or cleaning the A/C system internally is one of the most important steps in auto A/C service to restore the system when there is any...

Auto A/C Terms - Glossary
Foaming
In auto A/C systems, foaming is a term that is used to refer to the formation of small bubbles in the refrigerant oil. That typically happens when...

Auto A/C Terms - Glossary
Ford Fixed Orifice Tube - FFOT system
Like the Cycling Clutch Orifice Tube A/C system that General Motors developed in the late 1970s, the FFOT system is...

Auto A/C Terms - Glossary
Freeze Up
This term refers to two possible failures in an auto A/C system. On systems using a thermostatic expansion valve, a freeze up occurs when...

Auto A/C Terms - Glossary
Gauges or Gauge Set
The one essential diagnostic tool required for every air conditioning service procedure. For complete details, see Manifold Gauges.

Auto A/C Terms - Glossary
Head Pressure
Head pressures represent the pressure of the refrigerant in the A/C system on the...

Auto A/C Terms - Glossary
Heat
Heat is a form of energy that we all experience every day. That is because everything has some amount of heat. That is, everything has some amount of heat unless it reaches a temperature of...

Auto A/C Terms - Glossary
Heater Core
Although not part of the A/C system, the heater core is another heat exchanger. In a vehicle, the heater core is located in the same case as the evaporator because automotive A/C systems are known as...

Auto A/C Terms - Glossary
Heat Exchanger
Air conditioning is all about heat and heat transfer. That is why every A/C system includes two heat exchangers. A heat excahanger is nothing more than...

Auto A/C Terms - Glossary
Heat Index
Also referred to as the humidex, the heat index is a number that represents the effect of both the ambient air temperature and...

Auto A/C Terms - Glossary
Hg (in-Hg)
The chemical symbol for Mercury. It is used when...

Auto A/C Terms - Glossary
Heat Quantity
Heat is measured in different ways. When you use a thermometer, you are measuring the intensity of heat and that is expressed in degrees Fahrenheit or degrees Celsius. The quantity of heat is measured by...

Auto A/C Terms - Glossary
High Load - Heat Load
This is a condition that causes the A/C system to operate constantly to maintain maximum capacity. On systems with cycling clutches (CCOT) and orifice tubes, a high load or high heat load would mean that the compressor...

Auto A/C Terms - Glossary
High Pressure Line(s)
Every A/C system is divided into two sides. The high side is high pressure, high temperature refrigerant while the low side is low(er) pressure and temperature. The high pressure lines are the ones that...

Auto A/C Terms - Glossary
H Valve - Block Type Expansion Vavle
Originally used on Chrysler vehicles, the H valve or block type expansion valve as it is referred replaces the conventional Thermostatic Expansion Valve (TXV). Besides the appearance of the valve, the biggest difference is that the H Valve eliminates...

Auto A/C Terms - Glossary
High Pressure Relief Valve
High side pressures are typically between 2 and 2 and one half  times the ambient air temperature as expressed in degrees Fahrenheit (degrees F). However, refrigerant overcharge or extreme humidity can cause those pressures to rise excessively, and when that happens, the high pressure relief valve will...

Auto A/C Terms - Glossary
High Side
Every A/C system is divided into sides. The low side starts at the expansion valve or orifice tube, includes the evaporator and the hose that returns from the evaporator to the compressor. Low side accumulators are also part of the low side of the system. On the other hand, the high side of the system starts...

Auto A/C Terms - Glossary
High Side Service Valve - High Side Charge Port
Also called a charge port or access port, the high side service valve will be located on the system somewhere between...

Auto A/C Terms - Glossary
Humidity
Humidity can seriously effect the pressure gauge readings on your auto A/C system. The reason that humidity effects the pressures is that technically, high humidity alone can....

Auto A/C Terms - Glossary
In-Car Sensor
Vehicles with automatic temperature control systems will include various sensors that will help the controls maintain a more even and comfortable in car temperature. Part of the sensor string that helps maintain proper temperatures is the...

Auto A/C Terms - Glossary
Inches of Mercury - ( in-Hg )
In auto A/C service, vacuum is an extremely important part of regular service. Just before the system is recharged, a vacuum pump is connected to pull vacuum. That level of vacuum is expressed...

Auto A/C Terms - Glossary
Latent Heat
The term latent is a Latin term meaning hidden. It is used to describe the heat that is consumed or released when a substance changes state. In an A/C system, when the liquid refrigerant in the evaporator absorbs heat and boils or changes state, the heat it absorbs is...

Auto A/C Terms - Glossary
Latent Heat of Condensation
Refrigerant in the A/C system absorbs heat in the evaporator. When it does that, it changes state to vapor refrigerant, but the vapor does not change temperature. That is because the heat absorbed was consumed to cause the change of state, and the heat it absorbed is known as latent heat. When that refrigerant reaches the condenser,....

Auto A/C Terms - Glossary
Latent Heat of Evaporation
Every A/C system cools because the refrigerant in the evaporator is actually boiling and changing state to vapor refrigerant. In order to cause a liquid (refrigerant) to boil, it must, like water, absorb heat. The heat that is absorbed if known as....

Auto A/C Terms - Glossary
Leak Detector
One of the most common failures on automotive A/C systems is the loss of refrigerant through leaks. Service technicians will utilize a leak detector in order to...

Auto A/C Terms - Glossary
Low Head Pressure
The A/C system is divided into two distinct sides. The low and high side. There are typical pressure gauge readings considered to be normal for each side. When the high side pressure...

Auto A/C Terms - Glossary
Liquid Line
A/C systems are not only divided into high and low pressure sides, they are also divided into liquid and vapor sides. The liquid line of the A/C system is referring to the line that....

Auto A/C Terms - Glossary
Low Side
Every A/C system is divided into sides. Not only does the system have a liquid and vapor side, but it also has a high pressure and low pressure side. The low pressure side is...

Auto A/C Terms - Glossary
Low Side Service Valve - Charge Port
Typically the A/C system will include two charge ports or service valves. One each for the high and low side of the system. The low side service valve or charge port will be....

Auto A/C Terms - Glossary
Low Pressure Cut Out Switch
An electrical switch that is wired into the clutch circuit of the A/C compressor, the low pressure cut out switch will sense refrigerant pressures and...

Auto A/C Terms - Glossary
Low Suction Pressure
Suction pressures refer to the low side pressure gauge readings on an A/C system. When those pressures drop below...

Auto A/C Terms - Glossary
Magnetic Clutch
Auto A/C compressors are belt driven. The pulley that the belt attaches to will turn constantly whenever the vehicle is running. The magnetic clutch is a coupling device that will allow the internal portion of the compressor to...

Auto A/C Terms - Glossary
Manifold
Typically a part of the manifold gauge set, the manifold is usually made from aluminum or brass and is used to control...

Auto A/C Terms - Glossary
Manifold Gauges - Presure Gauges
The most basic tools required to test and service any automotive A/C system are manifold gauges. They are a testing assembly consisting of...