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T -312
1.6 SAFETY DEVICES
System components are protected from damage
caused by unsafe operating conditions with safety
devices. Safety devices that are connected to Carrier
T ransicold supplied equipment include a high pressure
switch (HPS), fuses (See Table 1-3.) and a fusible plug.
In addition, evaporator and condenser fan motors and
the main control box are protected independently
against high current draw by circuit breakers supplied by
the coach manufacturer. The evaporator and condenser
fan motors are also protected from high temperature
with internal thermal protection switches. If a condenser
fan motor safety device opens to stop the condenser fan
motor(s), the system may develop a high pressure
condition, which may open the high pressure switch
(HPS) to shut the unit down.
a. Pressure Switches
High Pressure Switch (HPS)
The high pressure switch (HPS) is installed in the
compressor center cylinder head and opens on a
pressure rise to shut down the system when high
pressure conditions occur. (Refer to: 1.3.d.)
During the A/C mode, HVAC system operation will
automatically stop if the HPS switch contacts open due
to an unsafe operating condition. Opening HPS
contacts de-energizes, through the main controller, the
A/C compressor clutch and condenser fan relays
shutting down the system.
b. Fuses
Fuses (F2 and F3)
Fuse (F2), internal to the controller, protects the
controller 12 vdc supply circuit from excessive current
draw. Fuse (F3) protects the controller 24 vdc output
circuit from excessive current draw.
c. Thermal Switches
Condenser Motor Overloads (CMOL1 and CMOL2)
Each condenser fan motor is equipped with an internal
thermal protector switch, condenser motor overloads
(CMOL1 and CMOL2). If excessive motor temperature
exists, the CMOL switch will open to de-energize the
corresponding condenser fan relay (CFR1 or CFR2);
this will stop the affected condenser motor .
Table 1-3. Safety Devices (For Carrier Supplied Equipment)
Unsafe Condition Safety Device Device Setting
High compressor discharge
pressure
High Pressure Switch (HPS) Refer to 1.3.d.
Excessive current draw by the
controller 12 vdc supply circuit
Fuse (F2) Opens at 5 amps
Excessive current draw by the
controller 24 vdc output circuit
Fuse (F3) Opens at 10 amps
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