What causes the evaporator coil to freeze?

- Apr 03, 2018-

The evaporator is normally frost-free. After frost, it affects heat transfer, increases thermal resistance, reduces cooling effect and air flow, so the evaporator can only dew condensation.

There are five reasons for frosting:

  1, the expansion valve adjustment is too small, low pressure is too low;

  2, too little system refrigerant, evaporation pressure is too low;

  3, internal circulation filter plug;

  4, temperature control (or temperature sensor) failure, the compressor does not stop;

  5. The variable displacement compressor's energy control valve (pressure regulating valve) fails and the compressor is working at full capacity, causing low pressure and evaporator frost. Of course, the low pressure pressure is also affected by the ambient temperature and the temperature of the cab. For the tube-belt evaporator, because it is only one head into the other, the side of the advanced liquid is colder, and then gradually does not cool, which is a phenomenon common to the sedans. The temperature difference between the left and right sides of the evaporator is a variety of factors, such as the compression efficiency of the compressor, the adjustment performance of the expansion valve, and the degree of sealing of the evaporator bellows. The system can not be too much oil! Do not store oil in the evaporator! The wall thickness of the evaporator of the auxiliary factory must not be too thick! Pay attention to the leakage of the evaporator!


Compressor will not automatically stop cooling all the time, first check the reason for non-stop. Such as temperature control temperature package is in place; temperature control adjustment is appropriate (appropriately reduce some, if not adjust the temperature control should be replaced); air conditioning computer control whether there is a fault.

The evaporator will freeze and the compressor will not stop. It should also check whether the inlet and outlet dampers of the evaporator box fan are blocked; if the fan gear is too small (should be larger, the circulating heat will increase, and the heat will naturally increase. better).

Check the control of the temperature windshield system, which is controlled by the servo motor. If the windshield system fails and the air cannot circulate, the evaporator will freeze.