312E, 312F, 313F, 316E, 316F, 318E, 318F, 320E, 320F, 323E, 323F, 324E, 325F, 326F, 329E, 329F, 330F, 335F, 336E, 336F, 340F, 349E, 349F, 352F, 374F and 390F Excavators and 336E MHPU and 349E MHPU Mobile Hydraulic Power Units Air Conditioning and Hea Caterpillar

Illustration 1	g02331097
(1) Expansion valve (2) Evaporator coil

Expansion valve (1) changes refrigerant of high pressure into refrigerant of low pressure. The high temperature liquid is also changed into a liquid of low pressure. The expansion valve provides a metered restriction. The metered restriction allows the high pressure liquid to be reduced to a vapor of low pressure. The expansion valve also adjusts the supply of liquid refrigerant to the evaporator coil.

In order to exercise the evaporator coil fully, an adequate amount of liquid refrigerant must be supplied to the evaporator coil. The cooling affect will decrease if the amount of refrigerant that is supplied to evaporator coil (2) is inadequate. This is true because the liquid refrigerant vaporizes quickly. On the other hand, if the supplied amount is too great, the excess liquid refrigerant that could not vaporize flows back to the compressor. Less cooling affect and a damaged compressor may result.