By the 1960s, air-conditioning was growing in popularity and market share. In 1969, 54 percent of cars sold in the United States were equipped with air-conditioning. Characteristics of cars from this era were the large compressors and large quantities of refrigerant used to make them work. A good sales pitch for this popular system was that it would increase resale value on the vehicle. As time passed, more and more vehicles were sold with air-conditioning as standard equipment.
Evolution of Heating and Air-Conditioning Systems
Cabin comfort in automobiles has seen many changes in the last 100 years. The industry has gone from not having cabin heat or an air-conditioning system to both becoming standard equipment. Many other advances have become common on cars and trucks as well. Some advancements that are available on modern cars and trucks include dual zone systems, rear heat and air systems, automatic temperature control systems, heated and cooled seats, and remote starting systems.
Dual zone climate control systems allow the driver and the passenger to have different air temperatures delivered to each side of the car. These systems are typically available on upscale vehicles and are made possible by having a more complex duct box system that has separate blend doors for each side of the vehicle. The drawback of these systems is that with more complexity in the system, more potential problems can occur when the vehicle begins to get older and in the higher-mileage category.
This dual zone climate control head allows the driver and the passenger to choose different temperature settings for each side of the vehicle. This control head also has the switches for the heated seats for the driver and the passenger.
The heat and air-conditioning controls are located at the roof area within easy reach of those in the second-row seats on the driver’s side. This control allows the blower speed, the temperature, and the mode to be chosen.
Many larger vehicles are equipped with rear heat and air systems that provide heat and air-conditioning directly to the rear section of the cabin. Having the added capacity to heat and cool the rear of a larger vehicle provides much improved comfort for the passengers of these vehicles. These systems require hoses and lines for heated coolant as well as pressurized refrigerant to be routed to the back section of the vehicle. This requires increased capacity for both the cooling system as well as the refrigeration system. In addition, these systems have more serviceable parts that must be operational as well as more potential leak locations for the coolant and refrigerant.
Automatic temperature control is another convenient option that is available on many modern vehicles. These advanced systems incorporate many sensors and computers to automatically control the temperature to the desired level. When these systems are in automatic mode, the operator selects the desired cabin temperature and the system works to move the cabin temperature to that level. Many of these systems are also equipped with dual zone capabilities, as mentioned previously.
Heated and cooled seats have become very popular in modern upscale vehicles. This added capacity to keep the occupants comfortable is a great advancement that is popular with consumers. Heated seats have been available for many years, but cooled seats have only been available for a few years.
Remote start systems have become a popular option in recent years. These systems are incorporated into the keyless remote systems and allow the user to start the vehicle by using the remote transmitter. Being able to start the engine with a remote control allows the heater or air-conditioning system to begin working before the driver enters the vehicle. This process allows the operator and passengers to enter a climate-controlled vehicle rather than having to wait for the system to get to the efficient zone after entering the unit.
This control head features automatic temperature control, dual zone, and rear defogger controls. Most vehicles with automatic temperature control also allow the operator to manually pick the air distribution point, blower speed, and air temperature.
The remote control for the door locks also features a button for the remote start function for this vehicle. Most vehicles with factory remote start require a sequence of buttons to be pressed in order to activate the function, which reduces the chances of accidentally starting the vehicle.
The rest of this book will provide information on how the air-conditioning and heating systems operate as well as how to diagnose and repair many of the common problems that could occur with these systems.
CHAPTER 2
HVAC SYSTEM
The heating, ventilation, and air-conditioning (HVAC) system is a fascinating series of components that all work together to help control the temperature and humidity of the cabin in a vehicle. These systems work by adding heat to the air in the duct box when the heat mode is chosen and removing heat from the air in the duct box when the air-conditioning (AC) mode is chosen. The information in this book will help you understand how the system works as well as how to troubleshoot and repair the system when it is not functioning properly.
Working Safely
Many precautions must be taken when working around the HVAC system on cars and trucks. This section provides information and procedures to help prevent injuries, accidents, and unwanted disposal of the fluids and chemicals within the HVAC system.
Always wear personal protection equipment (PPE) when performing repair and maintenance on a vehicle’s AC or heating system. Quality Z87-rated safety glasses will provide eye protection. Wearing quality latex or nitrile gloves protects the hands from potential frostbite.
Refrigerant
The substance inside the AC system that is used to flow through the components and remove heat from the cabin is called refrigerant. There are three main types of refrigerant that have been used by original equipment manufacturers (OEMS): R12, R134a, and R1234yf. All of them have some characteristics that need to be understood, and they will all be explained in greater detail later in this chapter.
All three of these refrigerants behave in a similar way. First of all, these substances are pressurized when in an enclosed vessel or when in a closed system, such as the AC system on your car. Care must be taken when working around this pressurized refrigerant because it can cause frostbite if liquid refrigerant gets on your body. A person could also get burned by the refrigerant while the system is in operation due to the high pressures and temperatures within the AC system. When working around refrigerants, do the following:
1. Wear safety glasses to protect from getting refrigerant in your eyes.
2. Wear latex or nitrile gloves to give a layer of protection for your skin.
3. Store refrigerant containers in a cool, dry location away from any heat source, such as a heater or direct sunlight.
4. Work with confident and meaningful actions when connecting or disconnecting service hoses to the service ports on the AC system.
Cooling System
The cooling system on cars and trucks must be dealt with in a safe manner. The liquid that transfers heat from the engine to the radiator as well as into the cab to the heater core is called coolant, and it is typically a mixture of antifreeze and pure water. Care must be taken to never attempt to