Specifications

Section 3
3-2
TOYOTA Technical Training
Most Toyota models now use a block-type expansion valve where both the
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vaporator inlet and outlet pass through the valve assembly. The capillary
tube is located inside the stream of refrigerant leaving the evaporator.
Due to the low temperature at this point, the valve is subject to blockage
by microscopic debris or internal ice if any water is present in the
refrigerant. Because of this, every system has some method to filter
out these elements.
Not all vehicles use an expansion valve like the one described above. Some
have a pressure-regulator at the outlet end of the evaporator. Other
manufacturers use a fixed-opening orifice tube to create the pressure
drop at the entry to the evaporator. This type of expansion valve relies on
the cycling of the compressor clutch to vary the flow and prevent icing.
The expansion valve is located at the inlet of the evaporator. A small
passage creates a pressure drop as the refrigerant enters the evaporator.
The pressure drop occurs as the small spray of refrigerant expands to fill
the large volume inside the tubes of the evaporator. Here is the sequence
of events:
• Warm, high-pressure liquid refrigerant flows to the expansion valve
• A low-pressure spray of cold refrigerant droplets pass through the
expansion valve into the evaporator
•
As the cold spray contacts the relatively warm tubing of the evaporator,
the refrigerant vaporizes (becomes a gas) and absorbs heat from
the evaporator and the air surrounding the evaporator
Block-Type
Expansion Valve
Releases high
pressure refrigerant into
evaporator.
Valve
Fig. 3-3
752f303
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