Air conditioning troubleshooting: the most common causes of failure

Air conditioning troubleshooting
Air conditioning troubleshooting

As most workshops know from their own experience, current compressed air systems are very maintenance-intensive – even if the manufacturers claim the opposite. For this reason, KRAFTHAND took part in a training session at Trainmobil at Wessels + Müller in Augsburg on potential sources of error and test options on the components of an automatic air conditioning system and put together some tips.

According to Stefan von Ahnen, Trainmobil’s climate expert, the most common mechanical sources of error in automotive air conditioning systems are leaks and blockages in the refrigerant circuit and the resulting compressor damage. According to the expert, it is important to determine the causes of the compressor failure, especially when replacing the compressor, in order to avoid another failure. The workshop must ask itself whether the fault is in the automatic climate control or in the refrigerant circuit. In addition, the workshop should know when and why an air conditioner is being flushed and how to do it properly.

Functional test

Exclude operating errors: In order to check the function of an air conditioning system and also to rule out possible operating errors by the vehicle driver, the mechatronics engineer should set the cooling to maximum and increase the engine speed according to the specifications of the automobile manufacturer. If cold air now comes out of the air outlet openings, he cannot assume that the air conditioning system is working properly, but should also observe the following points.

2. Initial diagnosis: The automotive specialist can quickly and easily determine whether refrigerant is being pumped by touching the high and low pressure lines by hand. The high pressure line must be warm (caution: there is a risk of burns in systems with high pressures); The low pressure line, however, must be cold. If this is the case, according to Ahnen, there is still refrigerant and the compressor is running.

3. Target pressure diagnosis: In order to determine damage to an air conditioning system, the automotive professional must check the system pressures with an air conditioning service device. If the target pressures (high pressure: 8 to 14 bar, low pressure: 1 to 3 bar) are reached at an ambient temperature of around 20 ° C, the problem of insufficient cooling is not in the refrigerant circuit.

4. Temperature outlet diagnosis: In addition, the specialist should also determine the air outlet temperature at the central air outlet openings in the dashboard using a suitable temperature measuring device. The appropriate test conditions such as outside temperature, ambient air pressure or air humidity of the respective vehicle manufacturer must be observed. As a rough guide, according to the training officer, an outlet temperature of no more than about 8 ° C at an ambient temperature of 20 to 25 ° C.

Check for leaks

The mechatronic technician cannot usually determine all the leaks despite the use of forming gas. If he does not hear any hissing noises or if the check using an electronic gas analyzer does not show any leaks in the system, practical specialist knowledge is required: In this case, the workshop specialist should shake the compressor pulley back and forth by hand (when the engine is not running) and can therefore easily do so Hear the hissing sound.

The refrigerant losses are primarily caused by leaky compressor shaft seals. The compressor shaft is centered during operation of the air conditioning system, which means that the sealing ring lies close to the compressor shaft. At standstill, however, the shaft lies on one side on the sealing ring and can be damaged. The leaks are favored if the compressor is not switched on in winter and no oil is added to the shaft seal


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