Valeooscope - Air Conditioning System Thermal comfort loop

11. The components of the A/C Loop

11.1.6 Evaporator freeze… a compressor killer !!

11.1.7 How to avoid the evaporator freezing

The temperature at the evaporator surface is conditio- ned by three main parameters: g The compressor suction pressure (set by the co pressor) g The flow of refrigerant in the evaporator (set by the Thermal eXpansion Valve-TXV) g The air flow rate through the evaporator fins

Evaporator freezing can be avoided by the system itself, as well as good practices during the A/C loop servicing. Good practices: g A restricted filter-drier, a low refrigerant charge or a faulty Thermal eXpansion Valve can lead to evapo- rator freezing. g A restricted air flow through the evaporator (cabin air filter or blower issue) can lead to freezing as well. A yearly maintenance preserves the A/C loop per- formances. Air inlet, cabin air filter, and blower performances are some of the fundamental points to be checked during servicing How does the system manages the freezing of the evaporator? This depends on the compressor technology, and can be achieved by:

Controlling the suction level g The suction pressure can be controlled only on variable capacity compressors Monitoring the evaporator temperature g In fixed-cylinder compressors, the suction pressure cannot be adjusted. The compressor must be stopped when its temperature ap- proaches 0°C to prevent the evaporator from freezing.

Evaporator freezing

If one of these parameters differs from the autho- rised limits, freezing may occur and may disable the refrigerant changing from liquid to gas. A massive return of liquid refrigerant to the suc- tion port jeopardises the compressor.

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