Why the air conditioner in the car does not cool well: a complete analysis of faults

A sharp decrease in the efficiency of the climate system, when barely warm or simply not cold enough air blows from the deflectors, most often indicates a critical drop in pressure refrigerant in the circuit or mechanical blocking of heat exchange. The driver may notice that when stopping at a traffic light, the temperature of the exhaust air rises, and when driving on the highway the cold returns, which is a classic sign of insufficient airflow. capacitor. Ignoring these symptoms leads to the compressor operating in oil starvation mode and eventual failure of expensive system components.

Another common scenario for the development of the problem is associated with the formation of an ice plug in the evaporator, when moisture from the air freezes on the radiator honeycombs and blocks the air flow. In this case, the system may initially cool well, and then suddenly stop passing air, requiring defrosting or replacement. thermostatic valve. Accurate diagnosis begins with a visual inspection and line pressure check, which allows you to separate electrical problems from mechanical damage or leaks.

Critical decrease in refrigerant level and circuit tightness

The most common reason why car air conditioner ceases to cope with its task, there is a banal leak of freon. Even a microscopic hole in the tubes or a loose connection of the seals leads to the gradual evaporation of gas, due to which the pressure in the system becomes insufficient for effective boiling of the refrigerant in the evaporator. Freon circulates in a closed circuit, and its quantity must remain unchanged for years, so any decrease in level requires an immediate search for the place of depressurization.

Leaks often occur in areas subject to vibration loads, such as at the junctions of aluminum tubes and rubber hoses, where the sealing material dries out over time. It is critical to understand that simply topping up without finding and fixing the leak is a temporary measure that will only delay compressor failure. In some cases, gas may escape through the compressor shaft seal, especially if the car has not been used for a long time in the winter, which has led to the rubber seals drying out.

• 🧊 Oily spots appear under the bottom of the car in the area of the front right wheel, where the condenser is usually located.
• 🔊 A whistling sound when the air conditioner is operating, indicating that gas is passing through a narrow opening.
• ❄️ Unstable air temperature: sometimes it blows cold, sometimes it blows warm, depending on the engine speed.
• 💨 Reduced overall system performance when, even at maximum settings, the air is only slightly cool.

⚠️ Attention: If a leak is detected, it is strictly forbidden to operate the system without repair, since compressor oil leaves the circuit along with the gas, which leads to jamming of the mechanism.

Contamination of heat exchangers and disruption of heat removal

The operating efficiency of any refrigeration machine directly depends on the system’s ability to remove heat to the external environment, and in a car the condenser (air conditioning radiator) is responsible for this process. Located in front of the main engine radiator, it actively collects fluff, dust, dirt and insects on its honeycombs, which creates the effect of a heat insulator and prevents normal heat transfer. When heat transfer is violated, the pressure in the system on the high-pressure side rises to emergency values, which forces the system to forcibly turn off the compressor or drastically reduce its performance.

The problem of pollution is especially acute in the summer, when the temperature difference between the hot air outside and the refrigerant inside the tubes must be maximum for effective condensation. A dirty radiator cannot transfer heat, the gas does not change from gaseous to liquid at the required speed, and an insufficiently cooled mixture enters the evaporator. Regular cleaning of the condenser using a special chemical cleaner and careful blowing with compressed air can restore the system to 30% of lost efficiency.

It is also important to take into account the condition of the main radiator of the engine cooling system, since they work in pairs. If there is a “fur coat” of dirt between them, then the hot air from the engine additionally heats the condenser, nullifying all the efforts of the air conditioning system. In such cases, it may be necessary to dismantle the “TV” (radiator frame) for high-quality pressure washing of all elements, but taking precautions so as not to bend the soft aluminum honeycomb.

Compressor and drive malfunctions

The compressor is the heart of the system, and if it is not cooling well, it may be due to worn internal components such as the piston group or valves. During long-term operation or operation on contaminated freon, gaps develop, which is why the compressor ceases to create the necessary pressure difference between the high and low pressure circuits. As a result, the gas simply circulates through the system without having time to compress and cool to the required temperature.

The electromagnetic clutch, which transmits torque from the engine pulley to the compressor shaft, requires special attention. If the gap between the pressure plate and the pulley is too large due to wear or dirt, the clutch may slip or not engage at all, especially on a warm engine due to thermal expansion of the metal. Electromagnet may also fail electrically, breaking the switching circuit, which is diagnosed by checking the voltage at the connector when the button is turned on A/C.

• 🔩 Extraneous noise, clanging or hum when the air conditioner is turned on, indicating the destruction of the bearing or internal mechanisms.
• 🛑 Visually noticeable slippage of the clutch pulley when the engine is running.
• ⚡ No characteristic click when turning on the climate activation button.
• 📉 Voltage drop in the on-board network when trying to turn on the compressor.

Problems with cooling fan and electrical

In urban conditions, when the car is stuck in a traffic jam or at a traffic light, the natural blowing of the radiators by the oncoming air flow is not enough, and the electric fan comes into operation. If fan does not turn on, operates at low speeds or rotates jerkily, the pressure in the system instantly increases, causing an emergency shutdown of the compressor by the high pressure sensor. This is one of the most common reasons why the air conditioner cools well on the highway, but stops cooling in the city.

Electrical diagnostics include checking fuses, fan control relays and the motor itself. Often the cause of failure is oxidation of contacts in connectors due to the ingress of moisture and reagents, which leads to loss of the control signal. It is also worth checking the freon pressure sensor, which sends a signal to turn on the fan; if it is faulty, the system “does not know” that it is time to activate the radiator airflow.

⚠️ Attention: Operating a vehicle with the fan not working in hot weather can cause the engine to overheat and the antifreeze to boil, even if the air conditioning is turned off.

Cabin filter clogged and evaporator frozen

Sometimes the reason for poor cooling lies not in the refrigeration unit itself, but in the interior ventilation system. Clogged with dust and leaves cabin filter creates aerodynamic drag, which causes the air flow through the evaporator to become too weak. At low air flow rates, the heat exchanger releases cold ineffectively, and the evaporator itself can become covered with an ice crust, completely blocking the air passage.

Freezing can also be caused by a faulty evaporator temperature sensor or a stuck thermostatic expansion valve (TEV) that is supplying too much freon. In this case, the system works cyclically: it blows cold for several minutes, then the ice blocks the honeycombs and the air flow disappears completely. After turning off the air conditioner for 10-15 minutes, the ice melts and the cycle repeats again.

To prevent such situations, it is recommended to change the cabin filter at least once a year or every 10-15 thousand kilometers. In a metropolis with high dust levels, it is better to reduce the replacement interval to 5-7 thousand kilometers, which will have a positive effect not only on the operation of the air conditioner, but also on the health of the driver.

Diagnostics and methods for restoring efficiency

Comprehensive diagnostics of the air conditioning system begins with connecting a pressure gauge station, which shows the pressure in the high and low pressure circuits with the engine running and stopped. Normal values ​​depend on the ambient temperature, but are usually around 2-2.5 bar on the low side and 12-15 bar on the high side when the compressor is running. Deviations from these values ​​make it possible to accurately determine the nature of the malfunction: lack of freon, clogging or mechanical failure.

If the pressure gauges show normal pressure, but there is no cold, check the air temperature at the outlet of the deflectors using an electronic thermometer. The difference between the temperature at the entrance to the system (in the cabin) and at the exit should be at least 10-12 degrees Celsius. A lower temperature delta indicates problems with heat transfer or mixing of air flows due to a malfunction of the climate control dampers.

Restoring functionality often requires evacuating the system to remove moisture and air, which also negatively affect cooling efficiency. After vacuuming, filling with the exact amount is carried out freon and oil specified by the manufacturer on the plate under the hood. Self-filling “by eye” or by weight of the cylinder without pressure gauges often leads to incorrect operation of the system.