Car Air Conditioning System Malfunction - Common Causes And Solutions

Indispensable in the summer to escape the scorching heat, and invaluable in winter for defogging windows – living without air conditioning is hardly bearable these days. Moreover, it's challenging to sell a car without air conditioning, as it's highly valued.

Problems with the air conditioning can't always be solved by simply recharging the system. This guide explains the most common causes and symptoms of a malfunctioning air conditioning system.

Symptoms of a Malfunctioning Air Conditioning System

The most obvious symptom is reduced cooling performance or the inability to turn on the air conditioning. In older vehicles, where the air conditioning compressor works like a refrigerator's and is switched on and off via an electromagnetic clutch, a pressure sensor in the refrigerant circuit shuts off the compressor in case of significant refrigerant loss. This prevents it from restarting and getting damaged due to running dry.

Technically, not much happens in the event of a failure. Since the compressor is mechanically disconnected from the drive by the electromagnetic clutch, its shaft does not rotate, protecting it from seizing due to dry running – unless it seizes before the pressure sensor reports a refrigerant loss.

In modern air conditioners, where the compressor works with a valve that regulates the system's performance, the situation is more complex. There's no mechanical clutch, and the compressor is continuously driven by a serpentine belt. Therefore, in case of refrigerant loss, which also carries the compressor oil, the compressor can seize, and driving may become impossible.

This occurs when the internal resistance of the compressor exceeds the driving torque, generated by the friction between the compressor's pulley and the serpentine belt. If the compressor is blocked, even the best and most expensive serpentine belt will break faster than desired.

If the compressor still functions, the leak in the system must be located. A specialized workshop has several methods to check the refrigerant circuit's integrity:

• One method is to fill the system with a refrigerant that glows under UV light. Leaks can be detected after a reasonable time, even hours later. In modern vehicles, accessing refrigerant lines can be challenging due to their placement, often requiring removal of many body parts and engine covers.
• Another method is the nitrogen test, where the system is filled with nitrogen, and a solution is applied to the lines. This solution foams at leak points.

Common Leak Locations

Refrigerant lines made of too thin material corrode – if not the pipes themselves, then the clamps holding them to the body. Also, connections between lines and components are prone to leaks, especially if the seals are not replaced during disassembly and reassembly of an air conditioning component.

Condensers used from the factory are made as cheaply as possible: The pipes are often too thin, and the welds inaccurately placed. Add moisture and mud, and refrigerant loss is almost preprogrammed.

Faulty Air Conditioning Condenser

A common reason for reduced air conditioning performance is a faulty condenser. It's mounted in front of the engine cooler, making it a target for dust and dirt entering through the grille and bumper air intakes. This can clog or damage the fins between the condenser lines, leading to reduced performance, increased fuel consumption, and accelerated wear of the air conditioning compressor.

In the best-case scenario, cleaning the condenser fins is sufficient. If the vehicle's front design allows, this can be done without removing the bumper. However, if the contamination is advanced or damage is evident, removing the condenser becomes necessary.

Removing the condenser also means the system must be emptied. A special device in many workshops separates the oil from the extracted refrigerant and weighs both. The weight, usually indicated on a label under the hood, shows how much refrigerant has escaped.

If the refrigerant loss is minimal, it can be assumed that the system is largely leak-free, as even new cars lose about 10% of their refrigerant annually through tiny leaks or rubber hose pores. This is an easily diagnosable and fixable issue, often occurring in relatively new cars (due to cost-saving in materials, etc.).

Faulty Air Conditioning Compressor

The compressor can also lose refrigerant, which escapes through a small gap between the drive shaft and the compressor housing. The shaft seal isn't made to last forever, and even efficient air conditioning systems exhibit slight "sweating" in this area.

If it's an older compressor with an electromagnetic clutch on the shaft, a specialized shop should be able to offer a complete overhaul. The leakage usually accompanies natural wear of the compressor, which can be identified by loud operational noises like distinct rattling or howling.

Once the compressor seizes, metal shavings over time can enter the air conditioning system. If the compressor is replaced, these shavings can quickly destroy the new component, which must be avoided at all costs. Therefore, the air conditioning system must be thoroughly cleaned by flushing the system.

Faulty Air Conditioning Dryer

Furthermore, the air conditioning dryer can fail. This simple component, which dehumidifies the refrigerant, has a limited capacity. As a rule of thumb, it should be routinely replaced every two to three years.

The reason is straightforward: If the refrigerant circuit isn't sealed, a certain amount of air containing moisture enters the system, potentially damaging air conditioning components that come into contact with the refrigerant through corrosion.