Six myths about air conditioning

Did you know? Your workshop customers will definitely be amazed and you keep a cool head. We clear up six myths about car air conditioning when it comes to handling, maintenance and repair.

1. When it gets hot..

"It only makes sense to activate the air conditioning when it's really hot." This is what automotive professionals hear again and again from customers. The statement seems 'felt' completely correct. Why cool the air inside the vehicle when it's wet and cold outside?
But even an air conditioner is subject to wear and tear. If an air conditioning system does not run regularly, the lubrication of the air conditioning compressor, the seals and the hoses can no longer be guaranteed. Materials become porous, leading to leaks. The compressor oil in the refrigerant circuit binds water due to its hygroscopic properties. This also promotes the aging processes and wear and tear of the components. The consequences can be leaks and loss of refrigerant, the cooling capacity is reduced more and more.
However, running the air conditioner regularly during the colder seasons also has its practical benefits. The system removes moisture from the air in the interior and helps prevent fogged windows, for example when it rains. Added to this is the cleaning function. Moisture and dirt can cause bacteria and mold to settle in the ventilation ducts and on the evaporator of the air conditioning system if the vehicle is not used for a long time. Bad smells can also occur. If the air conditioning runs regularly, this is effectively counteracted. But beware! Most air conditioning systems in modern vehicles only start up at 3-5°C due to the system.

Do you advise your workshop customers to activate the air conditioning at least once a week for around 10 minutes, even in the colder months of the year? This way your customers keep a cool head even in midsummer. You suffer less from allergic reactions and don't have to wrinkle your nose.

2. When all else fails..

"An air conditioning service is only necessary if the performance of the air conditioning system drops sharply." This statement also belongs to the realm of myth. Because if the cooling capacity is already severely restricted or if the system no longer provides any cooling capacity at all, expensive damage to the system components can already have occurred.
In principle, the refrigeration cycle is never 100% tight. This means that refrigerant diffuses out via hoses or O-rings. In addition, components containing rubber age and become porous. The legislator has set a maximum permissible upper limit of 40g for vehicles with one evaporator and 60g for vehicles with two evaporators. More refrigerant should not escape in the year. If the loss is more than 10 percent per year, the system is leaking.

Too little refrigerant in the system not only leads to inadequate cooling, drying and cleaning performance of the system, but also to insufficient lubrication of the compressor and higher system temperatures. Permanent and expensive damage to the hardware cannot be ruled out. For this reason, an air conditioning check should be carried out every year and a complete air conditioning service every two years at the latest, even if the air conditioning feels like it is still working well. In addition to the work of an annual air conditioning check, the air conditioning service also includes replacing the refrigerant, the filter drier and the cabin filter. In addition, proof of competence is required for work on air conditioning systems.

3. Mix Impossible..

Extracting the old refrigerant and refilling it is part of every air conditioning service. "If the refrigerant R134a was used before, I can replace it with the new refrigerant R1234yf." No, that's not possible! What is clear to every automotive professional is by no means necessarily known to workshop customers. He thinks about the environment and would like to have the more environmentally friendly refrigerant (GWP value=4) filled into the system. However, this is neither technically possible (for safety reasons, the connection couplings on the air conditioning systems vary depending on the system and refrigerant), nor is it permitted! The automotive professional must have two air conditioning service units for vehicles with the two refrigerants R134a and R1234yf. Conversely, replacing R1234yf with R134a (for reasons of cost) is not easily possible and is also not legally permissible.

 The same applies to the refrigerant oil. It is used to lubricate the compressor and seal the system. Depending on the type of compressor (mechanical or electric), polyalkylene glycols (PAG) or polyol esters (POE) are used. The two oils must not be mixed! With an electrically driven compressor, the compressor oil comes into contact with components such as the coil. POE oils have a higher resistance and are therefore poorly electrically conductive. Fully synthetic PAG oils are increasingly used in air conditioning systems with R134a (good miscibility), they are hygroscopic and absorb moisture from the environment. However, when using PAG oils, the automotive professional must pay attention to the information provided by the vehicle manufacturer or the correct viscosity class (PAG 46, PAG 100, PAG 150). Standard PAG oils are not suitable for air conditioning systems with the new refrigerant R1234yf. However, the refrigerant oil PAG YF can be used both with R134a and with the new refrigerant R1234yf!
Polyalphaolefins (PAO) or multigrade oils represent a "universal solution". PAO oils do not bind moisture (not hygroscopic). They can be used as an alternative to the various PAG oils that are offered for R134a, sometimes together with the refrigerant R1234yf and for electric compressors. In any case, the car professional must ensure compliance with the product and manufacturer specifications!

4. The moisture has to go..

"The purpose of the evacuation is to get the refrigerant out of the air conditioning system." This statement is wrong! Rather, evacuation means removing moisture from the air conditioning system. A high proportion of water in the air conditioning circuit, for example, together with the compressor oil, can lead to the formation of an emulsion. In addition, the combination of refrigerant, moisture and escaping dryer granules can lead to the formation of silicic acid and other substances and damage to components. If there is too much moisture in the air conditioning system, there is a risk that the expansion valve will ice up. The circulation of the refrigerant is then severely restricted.
An evacuation is accompanied by the formation of a vacuum. You have to know that moisture (water droplets) can only be removed from the system in the gaseous state. The greater the vacuum, i.e. the more powerful the vacuum pump, the faster the evacuation or dehumidification process runs. Of course, the air conditioning must be absolutely tight.

5. Leak detection..

It can happen that an air conditioner is almost entirely free of refrigerant due to a leak. "If there is no refrigerant in the system, it has to be refilled with refrigerant and contrast agent to detect the leak." That's also wrong! The principle of 'bicycle tube and sink' should not be applied here. Since there is a risk of refrigerant escaping again, this is not permitted according to the Chemicals Protection Ordinance. An air conditioning system may only be refilled if the system is absolutely tight! Deliberately draining refrigerant is an administrative offense and will be punished with fines of up to EUR 50,000.
A leak search according to the manufacturer's specifications is the alternative. Leak detection is made easier by the ultraviolet contrast media added to the refrigerant, which are visible using a special lamp. The use of special forming gas is also an alternative. The gas, consisting of 95 percent nitrogen and 5 percent hydrogen, is filled into the empty air conditioning system at a pressure of around 10-12 bar. The hydrogen content serves as a trace gas, which in turn can be detected with a special electronic leak detector.

6. Well rinsed is well chilled..

"Flushing the air conditioning system is only necessary if it is filled incorrectly". That is not correct! For example, if the automotive professional replaces a defective air conditioning compressor, the air conditioning system must also be flushed in any case. This is the only way that any metal chips, sludge or dryer granules can be safely removed before refilling. Since compressors, expansion and throttle valves or the filter drier or accumulators cannot be flushed, they must be bypassed with adapters during the flushing process. After completing the flushing process, the valves, filters and all O-rings on the connecting lines must be replaced.
Due to the increasingly compact design of the condensers, it is quite possible that not all residues can be removed during rinsing. Here it is actually at the discretion of the car professional whether the capacitor also needs to be replaced.


The intermediate inspector (a sight glass module) is used to visually check the purity of the refrigerant if contamination is suspected. The rinsing process itself can be done with refrigerant or with a chemical solution. The specifications of the component and vehicle manufacturers must be observed here.