If only warm air comes out of the air conditioning system instead of cold air, it is usually too late. If metallic abrasion or other harmful parts have entered the air conditioning system, a thorough internal cleaning of the air conditioning system is absolutely essential. Defective compressors in particular often lead to chips in the pipes. Does a real workshop professional leave the old oil in the lines after an engine change? No, never. This also applies to the air conditioning system. Because only those who also flush the refrigerant circuit can avoid annoying consequential damage.
A flushing is mandatory every time the compressor is replaced. Otherwise, the next defect is imminent: at best after a year, at worst after just two weeks. The fatal situation for the workshop: Such damage is not covered by the warranty. Over time, small deposits build up in the air conditioning system - even without replacing parts. Such oil or dirt deposits in the refrigerant circuit can only be completely removed from the system with a flush.
Flushing is time-consuming, but it's worth it. There are different methods, such as flushing with nitrogen (particularly suitable if individual components need to be cleaned or dried before (re)installation), or flushing with chemical agents followed by a nitrogen flush to dry. However, neither method is optimal.
The simplest and gentlest form of cleaning is certainly flushing with an air conditioning service unit, a separate flushing kit with replaceable pre-filter and refrigerant. This method is prescribed by most vehicle manufacturers. Flushing is always carried out against the normal flow direction of the refrigerant. As some components (such as the filter dryer/accumulator, the compressor, the expansion valve or the fixed throttle) cannot be flushed, they must be bypassed or replaced using adapters.
Many modern capacitors cannot be flushed due to their design (parallel flow) and the combination with the filter-drier. This only works with older types (so-called serpentine condensers). In vehicles with a second evaporator in the passenger compartment, this must be flushed separately. As a general rule: When replacing the compressor, the vehicle professional must always replace the filter dryer and expansion valve/fixed throttle.
Each flushing cycle should be carried out three times and the pre-filter of the flushing unit should be replaced after each vehicle (flushing process). Once all removed or replaced parts have been refitted, a leak test must be carried out and the system must then be evacuated for at least 20 minutes.