What You Need to Know About How a Car A/C Works

You’re thankful your car A/C helps keep the cabin cool on sweltering summer days. But do you understand how the A/C system works and how to keep it maintained? This guide covers the nitty gritty details of your vehicle’s A/C to help you catch problems early on and keep it in excellent shape. 

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How Does a Car A/C System Work?

Believe it or not, there’s no ice machine hidden inside your car A/C. That blast of chilly air is actually hot air with the heat removed during a multi-step process. 

When you turn the A/C on, the compressor compresses the system’s refrigerant, raising its pressure and temperature. The refrigerant loses heat as it flows through the condenser. Typically, it then passes through the receiver/dryer, where contaminants and moisture are removed. 

Then, it’s on to the expansion valve. Here, the refrigerant loses pressure and temperature as it enters the evaporator, chilling it.

The evaporator is like a mini radiator in the dashboard. Air gets blown through the chilled evaporator, which cools and removes moisture from the air. The ventilation system blows that cool, dry air into the passenger compartment. Your air conditioning system works hard so you can get that refreshing, cold air. 

How Often Should My A/C Be Inspected?

There’s no set schedule for inspecting your A/C — it’s all about how the system feels.  Are you refreshed and cooled with full airflow when your vehicle's A/C is pumping? If you answered, “Yes, I am as cool as a cucumber,” you can cross A/C inspection off your list.

Do you fall into the “my A/C is not cold enough” or the “my A/C doesn’t work in the heat” side of the spectrum? Don’t sweat; stop in for an A/C Performance Check, and we’ll have you back on those hot summer streets cooler than ever. 

How Often Do I Need My A/C System Recharged?

Modern air conditioning systems don’t need to be recharged on a set schedule. Most drivers can go years before needing one. However, you’ll likely notice when it’s time for a recharge. Signs your A/C might need to be recharged include hot or warm air coming from the vents, refrigerant leak, weird smells coming from the vents, and an A/C clutch that won’t engage. (We'll cover all of these potential symptoms below!)

If you experience any of these problems, visit your local Firestone Complete Auto Care for an A/C Performance Check. Our expert technicians will get to the root of the problem.

What Are the Parts of a Car A/C?

To help keep your cabin cool, your A/C relies on several components. Let’s take a closer look at these A/C system parts and their roles in giving you that refreshing blast of cool air. 

What is the A/C Compressor?

The compressor is the core, primary part of every A/C system. They control temperature output with an electrically operated clutch. This clutch turns on and off whenever you change the temperature or if the HVAC module senses it has reached the desired temperature. If the ambient air temperature drops below the programmed value, the compressor clutch may not engage.

Signs of a Worn A/C Compressor

• Oil or refrigerant leaks (a professional can use special dyes to spot a refrigerant leak)
• Strange noises coming from under the hood while the A/C is on
• Erratic or failing A/C operation

What is a Compressor Clutch?

Before the compressor turns on, a special electromagnetic clutch (the compressor clutch) engages and disengages the compressor cycle. The compressor clutch engages the compressor, turning it on or off when commanded.

Symptoms of a Failing Compressor Clutch:

• Poor A/C performance
• Inability to turn the A/C on or off
• Clutch will not engage 

What is an A/C Condenser?

Consider the A/C condenser the master of turning hot refrigerant gasses into liquid. The condenser is mounted at the front of most vehicles, usually in front of the radiator. Outside ambient air passes through the condenser, condensing and cooling the hot refrigerant gas into a cool liquid refrigerant. 

Signs of a Worn A/C Condenser

• Leaks
• Clogged, corroded, or damaged fins or tubes
• Poor air conditioning performance

What’s a Receiver/Drier?

The receiver/drier is found on vehicles with a thermal expansion valve. It’s the safety net responsible for helping trap and prevent harmful debris and moisture from reaching the compressor and other vital A/C parts. The receiver/drier should be replaced anytime the A/C system is opened for repair or if a technician determines moisture or debris has damaged your receiver/dryer performance.

Symptoms of a Worn Receiver/Drier:

• Poor air conditioner performance
• Moisture on glass and/or inability of defroster to remove moisture from glass and windows

What is an Accumulator?

An accumulator is similar to a receiver/drier but is only on vehicles with an orifice tube. If you have an accumulator, you do not have a thermal expansion valve.

The accumulator:

• Monitors and controls the amount of refrigerant that enters the evaporator
• Stores excess refrigerant so that it cannot enter and damage the compressor
• Filters debris and removes moisture from the A/C System

You will need to replace the accumulator if the A/C system is opened for repair or if a technician determines moisture or debris has damaged your accumulator’s performance.

What is a Thermal Expansion Valve/Orifice Tube?

The orifice tube or thermal expansion valve is located between the condenser and the evaporator. It constantly monitors the pressure and temperature of your A/C system to determine the exact amount of refrigerant that can safely enter your evaporator. If too much or too little refrigerant enters the evaporator, you could have a big problem.  

An orifice tube may also contain a fine mesh screen to block contaminants from the rest of the system.

Signs You May Need a New Orifice Tube or Thermal Expansion Valve:

• Poor A/C system performance
• A technician has determined it’s dirty or clogged

What is an Evaporator?

The evaporator is located behind your dash and is responsible for cooling cabin air and removing moisture. Low-pressure refrigerant traveling through the evaporator cools it. This allows the evaporator to absorb heat from the cabin air, dropping the temperature of the air blowing out of the vents. If cold, refreshing air hits your face, the evaporator is working like a champ.

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Symptoms of a Worn Evaporator:

• Poor A/C system performance

What is the Clutch Cycling Switch?

The clutch cycling switch cycles the compressor according to the pressure in the accumulator. This action helps to prevent the evaporator from freezing. Although most cars can blow air at temperatures as low as 60 degrees, the temperatures inside the evaporator core can get cold enough to freeze the entire core completely. 

The clutch cycle’s job is to ensure the evaporator doesn’t reach the point of glacier temperatures.

Symptoms of a Failing Clutch Cycling Switch:

• Evaporator freezing up
• Evaportor does not get cold enough

What is Refrigerant?

Refrigerant (often referred to by the DuPont trade name Freon) is a specially formulated cooling agent that can transform from a liquid to a gas and back again. It absorbs and releases heat, ultimately leaving cool air behind.

Different devices, such as your home refrigerator, home A/C system, or vehicle, may use different refrigerants. They may or may not be the same. 

What Are the Different Types of Car Refrigerant?

The three common car refrigerants are R-12, R-134a, and R-1234yf. Different refrigerant types require different charging hoses, so check which one your vehicle is it in earlier models.

• R-12: R-12 is the original chlorofluorocarbon (CFC) Freon used in car A/C systems until the mid-1990s. It was banned after the EPA discovered that it depletes the ozone layer. Vehicles manufactured pre-1995 often use R-12, but you can retrofit them with an R-134a system.

• R-134a (HFC-134a): Your vehicle likely uses R-134a (also called HFC-134a). This refrigerant surfaced to replace R-12 once its environmental dangers were discovered. While R-134a is safer than R-12, and most vehicles use it, it’s still not the safest option for the ozone. Manufacturers have recently phased it out.

• R-1234yf (HFO-1234yf): To replace the phased-out R-134a, manufacturers created R-1234yf (also called HFO-1234yf), a hydrofluoric-olefin refrigerant. R-1234yf is an even more environmentally friendly refrigerant. It should be in cars manufactured after 2021, though you may find it in earlier models. 

What is a Refrigerant Charge Port?

The refrigerant service port is the connection point where new refrigerant can enter the system during an A/C system recharge or where you can remove refrigerant from the A/C system. There is a service port located on the low side and high side A/C lines. Only properly equipped, certified, and qualified persons should perform A/C recharging services. The EPA (Environmental Protection Agency) requires anyone who services automobile air conditioning systems to be EPA Section 609 Certified. 

Cool Down with Firestone Complete Auto Care

The last thing you want is to sweat in your car every time you drive to work or pick up groceries. If you notice any change in your car A/C’s performance, it’s time for an inspection. Schedule an appointment with the experts at your local Firestone Complete Auto Care today.

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Components of the AC system - Compressor Assembly

Compressor Assembly
The Compressor assembly consists primarily of the Compressor and Clutch.

The A/C Compressor compresses the refrigerant gas to a higher pressure. It is the heart of the AC system.
It is shown here with the attached Clutch. The clutch is an electromagnet.

Here's how things work...

The mechanical power from the engine crankshaft is transferred to the AC Compressor + Clutch through the Drive belt. Drive belts may be called by various names - e.g. V belt, Serpentine belt etc. (In addition to driving the AC Compressor Clutch it also drives other things e.g. the power steering pump, the alternator, water pump etc.)

The clutch ( electromagnet) is powered by the AC Clutch Relay which sits inside the fuse box. When you press the A/C Switch inside the cabin, it causes the current to flow through the relay, and powers the field coil inside the clutch. The generated magnetic field in turn attracts the Clutch drive plate outwards so that presses against the inside of the rotating pulley and then rotates with it. The drive plate is mounted on the central shaft which in turn drives the compressor. The entire clutch drive plate is immersed in clutch oil for longevity, this is retained using a system of oil seals and covers.

Here is an exploded view of the Clutch...


The AC Compressor is an extremely complex unit. It is not serviceable at your FNG or A.S.S. because of the extremely high tolerances of manufacturing and assembly. There are two basic types- reciprocating type and rotary type.

Here are four different kindsof compressors manufactured by

Quote:

1) Fixed displacement Swash Plate Type Compressor

Structure
This compressor is constructed from the components shown in the illustration.
The piston completes a 360 cycle when power from the engine causes the shaft and swash plate to rotate.
One piston is comprised of cylinders on both sides. The ends of the piston intake pressurize and discharge refrigerant.
Operation
In the cylinder shown in the right of the illustration, the suction valve is opened when the piston moves to the left. The pressure difference between the suction shaft within the housing and inside the cylinder causes refrigerant to enter the cylinder through the suction valve. Conversely, when the piston moves to the right, the suction valve is closed and the refrigerant is pressurized. Continued pressurization increases the pressure of the refrigerant in the cylinder, causing the discharge valve to open. The refrigerant then flows to a high-pressure pipe. (The suction and discharge valves prevent flow back of the refrigerant.)
The balance of characteristics and reliability in this compressor make it suitable in a wide-range of vehicles around the world, such as small vehicles, mini-vans, large busses, and construction equipment.

2) Vane type compressor

Structure

This compressor is constructed from cylinders and 5 vanes built into the rotors, as well as 2 discharge valves and front and back side plates.
The 5 vanes rotate in tandem with the rotors while contacting the wall inside the cylinder.
Operation

Cylinder volume increases with rotor rotation, causing refrigerant to flow into the cylinder shaft from the suction port.
The refrigerant is sealed within the cylinder by the vanes, and is compressed by the rotation of the rotor. It is then discharged from the discharge port once it reaches outlet pressure.
The compressor is equipped with two suction and discharge ports. Refrigerant is discharged 10 times for each rotation.

3) Scroll type Compressor

Structure
This compressor is constructed from one fixed and one rotating scroll in an offset spiral configuration.
Shaft rotation creates spaces of varying volume between the 2 scrolls, causing refrigerant to be sucked in and compressed.
Operation
As the rotating scroll moves, the space between the two scrolls also moves, causing the volume of this space to gradually decrease.
Refrigerant flows in from the suction port and is gradually compressed by the rotating scroll rotation. It is discharged from the discharge port after approximately 3 rotations.
Refrigerant is actually discharged once for each rotation.
It is an extremely quiet and efficient compressor used mostly in small and light cars.

4) One-way swash plate internally controlled type

The illustration shows the construction of this compressor.
Structure
Refrigerant intake and compression methods are almost the same as those for the Fixed Displacement Swash Plate Compressor. Unlike the fixed displacement type, however, there is only one cylinder.
Operation
The required amount of refrigerant gas is sucked in and compressed by changing the pressure balance within the compressor. The swash plate angle can be adjusted, which forces the piston to make larger or smaller strokes. This enables stable temperature control and improved driving feeling.
Displacement control can be achieved by either internally controlled variable displacement or externally controlled variable displacement methods.

The Compressor assembly consists primarily of the Compressor and Clutch.Thecompresses the refrigerant gas to a higher pressure. It is the heart of the AC system.It is shown here with the attached. The clutch is an electromagnet.Here's how things work...The mechanical power from the engine crankshaft is transferred to the AC Compressor + Clutch through the. Drive belts may be called by various names - e.g. V belt, Serpentine belt etc. (In addition to driving the AC Compressor Clutch it also drives other things e.g. the power steering pump, the alternator, water pump etc.)The clutch ( electromagnet) is powered by thewhich sits inside the fuse box. When you press the A/C Switch inside the cabin, it causes the current to flow through the relay, and powers the field coil inside the clutch. The generated magnetic field in turn attracts the Clutch drive plate outwards so that presses against the inside of the rotating pulley and then rotates with it. The drive plate is mounted on the central shaft which in turn drives the compressor. The entire clutch drive plate is immersed in clutch oil for longevity, this is retained using a system of oil seals and covers.Here is an exploded view of the Clutch...Theis an extremely complex unit. It is not serviceable at your FNG or A.S.S. because of the extremely high tolerances of manufacturing and assembly. There are two basic types- reciprocating type and rotary type.Here are four different kindsof compressors manufactured by Toyota for their cars... 1) and 4) are reciprocating type, where as 2) and 3) are rotary type.

Last edited by joybhowmik : 3rd May 2014 at

00:45

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