146 Auto Heating and Air Conditioning Copyright by Goodheart-Willcox Co., Inc. an electrical switch that opens and closes at certain tem- peratures, or a temperature sensor connected to a control module. A typical evaporator temperature control switch is shown in Figure 9-6. Th e design and function of various temperature sensors will be discussed in Chapter 10. Interior Air Filter Th e air intake side of some blower case assemblies con- tain an interior air fi lter. Th is fi lter is usually a conventional fi lter. In some cases, it may be electrostatically charged. Th e fi lter removes dust, pollen, and in some cases, odors from the incoming air. Th is keeps the evaporator from becoming restricted, and the inside of the vehicle cleaner, Figure 9-7. Condensers Th e condenser is the heat exchanger that removes heat from the refrigerant, allowing it to condense from a vapor to a liquid. On vehicles with water-cooled engines, the con- denser is either located ahead or mounted beside the vehicle radiator. On an air-cooled engine, the condenser is placed where the cooling system blower can draw air through it. Since the condenser operates under higher pressures than the evaporator, it is made from a heavier gauge of alumi- num or copper tubing, usually painted black to aid in heat transfer. Condenser Design Most modern condensers are cross-fl ow types, which means the tubes are placed so refrigerant fl ows across the condenser. Th ere are three primary types of condensers in use. Th e fi rst condenser is the tube and fi n design. Tube and fi n condensers have been in use for many years. Th e one most oft en used is referred to as a 3/8 inch tube design, Figure 9-8A. A variation on the tube and fi n design has a smaller diameter tube (6 mm or 1/4 inch), Figure 9-8B. In some cases, the 6 mm condenser may have an internal baffl e Figure 9-4. A serpentine evaporator is a single flat tube that passes snakelike through the cooling fins. (Subaru) Figure 9-6. On some refrigeration systems, an evaporator temperature control device is installed at the evaporator outlet or in the evaporator fins. This sensor is used to control clutch cycling. (Chrysler) Low-pressure cut-off switch Cycling clutch switch Suction line Capillary tube well Capillary tube "H" valve Figure 9-5. A—Most sensing bulbs are attached to the evaporator with clamps and covered with insulating material, often called dum-dum or presstape. B—A few expansion valve bulbs are installed in a cavity formed in the evaporator outlet tube. Insulation Capillary tube Sensing bulb Clamp A B