1--4
©
2015 Mobile Climate Control
T-367Rev. 05/2015
1.5 SAFETY DEVICES
System components are protected from damage
caused by unsafe operating conditions with safety
devices. Safety devices with Mobile Climate Control
supplied equipment include high pressure switch
(HPS), low pressure switch (LPS), fusible plug,
circuit breakers and fuses.
a. Pressure Switches
High Pressure Switch (HPS)
During the air conditioning cycle, compressor clutch
operation will automatically stop if the HPS switch
contacts open due to an unsafe operating condition.
Opening HPS contacts de-energizes the compressor
clutch shutting down the compressor. The high
pressure switch (HPS) is installed at the compressor
assembly. See paragraph 1.3 for specifications.
Low Pressure Switch (LPS)
The low pressure switch is installed on the
compressor assembly and opens on a pressure drop
to shut down the system when a low pressure
condition
occurs.
See
paragraph
1.3
for
specifications.
b. Fuses and Circuit Breakers
The Relay Board is protected against high current by
an OEM supplied circuit breaker or fuse located in
the bus battery compartment (100 Amp for 24 VDC
systems is recommended). Independent fuses and
circuit breakers protect electrical circuits from high
current conditions. During a high current condition,
the circuit protection may open.
c. Ambient Lockout
Auto Mode
Opens Compressor Output at: 43
°
F (6.1
°
C
)
Closes Compressor Output at: 47
°
F (8.3
°
C
)
Defrost Mode
Opens Compressor Output at: 28
°
F (-2.2
°
C
)
Closes Compressor Output at: 32
°
F (0
°
C
)
The ambient temperature sensor measures the
condenser inlet air temperature. These settings
protect the compressor from damage caused by
operation at low pressures.
d. Unloader Operation
The compressor is equipped with two unloaders to
allow compressor operation at 33%, 66% or 100%
capacity.
Low Pressure Control
Energizes Unloader Output 1 (Unloads) at: 25 psig (1.7
bars)
De-energizes Unloader Output1 (Loads) at: 32 psig (2.2
bars)
Energizes Unloader Output 2 (Unloads) at: 21 psig (1.4
bars)
De-energizes Unloader Output1 (Loads) at: 28 psig (1.9
bars)
High Pressure Control
(below 87 F (30.8C
)
Energizes Unloader Output (Unloads) at: 300 psig (20.7
bars)
High Pressure Control
(above
92 F (33.6C
)
Energizes Unloader Output (Unloads) at: 320 psig (23.4
bars)
In response to the high pressure conditions
above, the unloader remains energized for 2
minutes. Once the pressures return below the
parameters listed, the unloader circuit will de-en
ergize.