Factory Installed Refrigeration System Components
1. Thermostatic Expansion Valve (TXV)
Each unit is equipped with a Thermal
Expansion Valve on each refrigerant
circuit. The valve controls the flow
of liquid refrigerant entering the
evaporator coil by maintaining a
constant, factory-set superheat of
10°F. The valve is adjustable and is
located on the side of the evaporator
coil and can be accessed through the
coil panel access door.
2. Refrigerant Distributor
Attached to the TXV is a refrigerant distributor.
The refrigerant distributor evenly distributes the
refrigerant to each circuit of the evaporator coil to
provide optimum performance.
3. Evaporator Coil
The coil is located in the supply airstream. In the
DX system, the liquid refrigerant is expanded in the
TXV and it then flows through the evaporator coil.
The refrigerant enters the coil as a low temperature
liquid/gas where it eventually boils into a low
temperature, low pressure gas prior to going
into the compressor. As the refrigerant passes
through the evaporator coil, it absorbs heat from
the airstream. To ensure proper operation, the coil
surface must be cleaned so that air movement over
the coil provides the necessary heat transfer.
4. Low Limit Pressure Switch
The unit includes a low limit pressure switch
(located in the compressor compartment). The
switch is installed in the suction line and shuts off
the DX system when the suction pressure drops to
50 psi for R-410A. The switch has a built in auto-
Evaporator Coil
Reheat Coil
Condenser Coil
M
1
2
3
4
13
5
12
9
11
13
10
8
13
14
7
15
6
Service Valve for Subcooling Gauge/
High Side Pressure Drop
Circuit A
Pressure Port for Troubleshooting Valve
Service Valve for
Superheat and Low
Side Pressure
Pressure Port for
Troubleshooting
Reheat Valves
High Side
Pressure Drop
Check Valve
reset, which will close the circuit and allow the
system to run when the pressure increases back to
90 psi for R-410A.
5. Compressors
Each unit will have either one or two high
efficiency scroll-type compressors. The scroll in
each compressor compresses the refrigerant in a
gaseous state to a high temperature, high pressure
gas.
Compressor Protective Devices:
Thermal Overload:
Each compressor is
equipped with an auto reset thermal overload.
High Temp Protection:
Internal devices within
the compressor protect it against excessively
high discharge gas temperatures.
Crankcase Heater:
Liquid refrigerant is
incompressible. Therefore, a crankcase heater is
installed around each compressor to boil off any
liquid refrigerant that may be absorbed into the
oil during idle periods. System power energizes
the heater; the heater should be allowed to run
24 hours prior to compressor start-up. See Start-
Up Checklist, page 23.
6. Condensing Coil
Each unit contains a condensing coil mounted
on the exterior of the unit. High temperature, high
pressure gas from the compressor enters the coil
and is eventually cooled into a high temperature,
high pressure liquid. The condensing fans move
air over the coil which pulls the heat out of the
refrigerant. To ensure proper operation, the coil
must be cleaned so that air movement over the coil
provides the necessary heat transfer.
19
Model MPX Make-Up Air Unit
Model XMPX Make-Up Air Unit
