For much of the summer, sweltering heat hits much of the country, turning the afternoon commute into a rather uncomfortable affair. Fortunately, the majority of all vehicles are now equipped with standard air conditioning (A/C), which has the ability to stop this stifling heat in its tracks.
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However, it should be noted that such systems are only effective when everything works as intended. Like any mechanical system, a vehicle's air conditioning is subject to occasional malfunctions due to the failure of individual components.
While great strides have been made in the design quality of various air conditioning components over the past decade, problems of one type or another still occur on occasion.
Read on to learn more about how your vehicle's air conditioner works, as well as the most common causes of a car air conditioner not blowing cold air since it's stuck in a vehicle that blows hot air out of the vents in the middle of a hot day isn't something everyone looks forward to.
How a car air conditioning system works
A vehicle's air conditioning system cools the air in the cabin by cycling the refrigerant in a closed loop through various physical states. Each of these state changes is directly correlated to temperature/pressure fluctuations in the system.
To facilitate proper operation, a vehicle's air conditioning system must contain the correct amount of refrigerant and be free of atmospheric air contamination.
Major components
Such systems also depend on a number of key components, each of which performs a vital function. These components, along with their general purpose, are as follows.
1 - Air Conditioning Compressor
The air conditioning compressor is responsible for pressurizing and cycling the system's refrigerant. This component has a magnetic clutch, which is engaged when called by a switched input or electronic request.
2 - Condenser
The condenser of an air conditioning system is a thin radiator-like device that is mounted behind the grille of a vehicle. As air passes through the condenser, the refrigerant inside changes from a gaseous state to a liquid state, releasing heat in the process.
3 - Dryer/Accumulator
Depending on the type of air conditioning system used, your vehicle is equipped with either an accumulator or a receiver drier. The former is only found in orifice tube systems, while the latter is a primary component of expansion valve systems.
These devices contain an industrial grade desiccant, which absorbs moisture from within the system.
4 - Metering Device (orifice tube/expansion valve)
All automotive air conditioning systems rely on a specialized metering device to dictate refrigerant flow. Many of these systems use an orifice tube to perform this task, while others use an expansion valve.
The exact location of these metering devices differs depending on the type of system.
5 - Evaporator Core
The evaporator core of an air conditioning system is a compact heat exchanger, which is mounted under the dashboard of a vehicle. The refrigerant passing through a vehicle's condenser changes from a liquid to a gas as it collects heat from inside the cabin.
Sensors
In addition to these main components, an air conditioning system also contains several sensors, all of which provide valuable information necessary for the proper operation of the system. These sensors, and their general purpose, are as follows.
1 - Low Pressure Switch
A low pressure switch is designed to detect a relative loss of refrigerant, as well as the accompanying lubricating oil. When the system low side pressures drop below a specified value, the low pressure switch is triggered to deactivate the system compressor, minimizing the risk of failure.
2 - High Pressure Switch
A high pressure switch is specifically designed to detect refrigerant over-pressurization in an air conditioning system. When system pressures rise for any number of reasons, the high pressure switch trips, interrupting the operation of the compressor clutch.
3 - Ambient Temperature Sensor
Modern automotive air conditioning systems use an ambient temperature sensor to relay real-time cabin temperatures. This information is used to increase cooling efficiency and maintain stable cabin temperatures over a wide range of conditions.
Causes of a car air conditioner not blowing cold air
Here are some of the most common causes of inefficient air conditioning system operation and cooling.
1 - Low Refrigerant
Low refrigerant is by far the most common cause of poor air conditioning cooling. This low refrigerant level is often caused by a previously undiscovered leak in the system. In all cases, the leak must be located and repaired if necessary, before the system is recharged.
2 - Excess Refrigerant
Although not as common as a low refrigerant condition, the efficiency of an air conditioning system can be stifled by excessive pressures. These higher-than-average pressures are often caused by system overcharging.
This usually occurs when a motorist attempts to introduce additional refrigerant into their vehicle's air conditioning system, using a home refill kit.
3 - System Restrictions
Restrictions within the air conditioning system can also cause poor cooling. A restriction chokes the flow of refrigerant, often resulting in unintended variations in system pressures. As a result, cooling often suffers quite dramatically.
4 - Air/Moisture Contamination
A vehicle's air conditioning system must be free of air/moisture contamination in order to operate at maximum efficiency. Even the smallest amount of air/moisture will cause erratic pressures in an A/C system.
Air is often inadvertently introduced into such a system when using a home charging kit. Excess moisture can also damage the desiccant in the receiver/dryer or accumulator of the system.
5 - Damaged compressor
A compressor, which pressurizes the refrigerant in an air conditioning system, can quickly fail if it runs out of oil. When this happens, all cooling stops in place and temperatures in a car's cabin begin to rise.
It is also advisable to flush the rest of the A/C system, after encountering an internal A/C compressor failure.
6 - Clutch Failure
An air conditioning compressor relies on the use of a clutch, which engages on command to drive the rest of the unit's internal components. This clutch is magnetically actuated and is released to the overrunning position when all power is removed.
When an A/C clutch fails, the system compressor cannot be engaged.
7 - Faulty cooling fan
Cooling efficiency can also suffer at the hands of a non-operational condenser fan. The condenser requires adequate airflow at all times in order to control high side system pressures.
If your vehicle is not blowing cold air at idle, but is cooling as expected during acceleration, a faulty cooling fan is almost always to blame.
8 - Faulty Sensors
If one of the many sensors in an air conditioning system were to fail, operation would be affected. The vehicle's computer would experience significant difficulties when trying to determine the correct duty cycles of the compressor clutch.
How much will it cost to repair?
The exact cost to repair the air conditioning system can vary greatly and often depends on the type/extent of the failure. In addition, the retail price of individual components of a vehicle's air conditioning system can differ significantly from one make or model to another.
In general, you can expect to pay between $100 and $250 to have your air conditioning system refilled with refrigerant. This assumes that no major system leaks are present and that refrigerant levels have only decreased due to gradual loss over several years.
On the other side of the spectrum, one can expect to pay much more if the internal air conditioning compressor fails. When this happens, the system itself must be flushed, before a new compressor is installed.
The system's metering and receiver/dryer (or accumulator) must also be replaced. Including labor, a job of this caliber typically costs between $500 and $1,100 on average.
How to prevent future air conditioning problems
In some cases, air conditioning system failures are inevitable. However, in other cases, such problems can be largely avoided with simple maintenance. This includes servicing your vehicle's air conditioning system at factory-specified intervals. For many makes and models, this service interval is typically around 100,000 miles.
A basic air conditioning service typically involves making sure your system is filled to capacity with refrigerant and that no obvious leaks are detected. A service technician will connect a set of gauges to your vehicle's A/C charge ports, before reading the system's high and low pressures. This will provide the technician with information on the system's charge rate.
If these pressures are lower than expected, the system's refrigerant will be topped off or, alternatively, evacuated and recharged. A technician will also search for the source of any offending leaks with a UV light. Repairs can then be made if necessary.
A preventive air conditioning service, such as the one described above, is very helpful when it is intended to extend the life of various components in your vehicle's air conditioning system.
Services of this type prevent your vehicle's air conditioning system from running out of refrigerant, which will cause the compressor to short cycle on a continuous basis. This short cycling ultimately accelerates wear and tear on the internal components of the air conditioning compressor, as well as its magnetic clutch assembly.
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