Talley UAC40-5/6-08, Technical Manual

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TM5-4120-375-14
THERMAL EXPANSION VALVE (CONT.)
LOCATION/ITEM ACTION
REMARKS
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4.
Expansion Valve
a. A refrigerant gas is said to be superheated when
its temperature is higher than the evaporating tem-
perature corresponding to its pressure at saturation
When a thermal expansion valve is set for optimum
superheat (in this case 6 degrees F or 3.3 d e g r e e s
C above the evaporating temperature of the refri-
gerant at a given pressure) the evaporator coil
operates at maximum efficiency.
That is, the
refrigerant gas does not become warm before reaching
the end of the coil, which would reduce the coils
cooling capacity, and the refrigerant does not
remain in the liquid state after passing completely
through the coil, which could result in severe
damage to the compressor. The superheat setting
of
a
thermal expansion valve can be adjusted by
varying the setting of a compression spring (7)
in the power assembly of the valve. This spring
tends to hold the valve closed against the pressure
in the sensing bulb and capillary tube; therefore,
the greater the spring pressure, the h i g h e r t h e
superheat.
Check superheat and adjust if
necessary, in accordance with the following
procedure: