Evaporator Section
The direct expansion coil is constructed of seamless cop-
per tubing expanded into aluminum fins. The tubes are
arranged for the counter-flow circuit and staggered to
provide maximum heat transfer. A pressure type distribu-
tor with hot gas inlet port and a heavy duty copper suction
header are included. Additional refrigerant circuit compo-
nents include thermostatic expansion valves with external
equalizer and insulated suction lines in the airstream.
Components of a Direct Expansion System
The evaporator is that part of the low pressure side of the
refrigerant system in which the liquid refrigerant boils or
evaporates, absorbing heat as it changes into a vapor.
Thermostatic Expansion Valve
The thermostatic expansion valve is a precision device
designed to meter the flow of refrigerant into the evapora-
tor, thereby preventing the return of liquid refrigerant to
the compressor. By being responsive to the temperature
of the refrigerant gas leaving the evaporator and the pres-
sure in the evaporator, the thermostatic expansion valve
can control the refrigerant gas leaving the evaporator at a
pre-determined superheat. Three forces that govern the
operation of the TXV are:
• The pressure created by the remote bulb and power
assembly (P1)
• The evaporator pressure (P2)
• The equivalent pressure of the superheat spring (P3)
System Operation Check
Verification of all control modes should be checked to en-
sure proper operation. Refer to
WARNING
Disconnect the main power switch to the unit before per-
forming service and maintenance procedures.
Distributor
Liquid line
Hot gas bypass line
Suction line
Expansion valve
Check valve on remote condensing
application (optional)
Evaporator coil
Figure 11: Direct expansion coil
P
1
P
2
P
3
Bulb clamp
Remote clamp
Diaphram
External
equilizer
port
Figure 12: Thermostatic expansion valve
CAUTION
In areas where scaling can become serious, a periodic
cleaning for the water-to-refrigerant heat exchanger is
recommended. Standard water coil cleaning procedure
should be followed which must be done by a qualified
service mechanic.
VCES-VHC-IOM-1F – VHC-36, -42 & -50
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