1-- 6
© 2012 Mobile Climate Control T-299 Rev. 08/2012
Freeze-Up Thermostat - Mobile Climate Control
systems use a freeze thermostat (freeze stat) wired in
series with the system pressure switches to control
the operation of the compressor clutch. Freeze-up
thermostats are used to prevent ice from forming on
the evaporator coil, which is an indication that liquid
refrigerat is getting back to the compressor.
Refrigerant - A refrigerant is a material that is used
to move heat from the passenger compartment to
the outside air. It is a substance that gives up heat by
condensing at high temperature and pressures and
absorbs heat by evaporating at low temperatures and
pressures. The heat transfer properties exhibited
when refrigerant changes state is the foundation of
the refrigerant cycle. Most MCC systems use R134a.
1
10
9
8
7
6
5
4
3
2
5
11
12
1 Compressor
2 Electro-Magnetic Clutch
3DischargeLine
4 Condenser
5 Filter-Dryer or Receiver-Drier
6 Liquid Line
7 Evaporator
8 Block Valve (TXV)
9 Freeze stat-(Coil freeze-up thermostat)
10 Suction Line
11 Suction Access Valve
12 Discharge Access Valve
Figure 1-9 Component Location Diagram
1.7 REFRIGERATION SYSTEM COMPONENT
SPECIFICATIONS
a. EXPANSION/BLOCK VALVE:
Superheat Setting: 8° F
b. PRESSURE SWITCHES:
High Pressure Switch: Norm ally closed, open on
pressure rise.
Cut-out at 400 psig - Cut-in at 300 psig.(±5%)
Low Pressure Switch: No rm ally closed, open on
pressure drop.
Cut-in at 25 psig. - Cut-out at 10 psig (±5%)
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