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Chapter 5
– System Controls
5-6
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Table of Contents-
Index5. Sleeper Unit Controls
The most familiar type of temperature control is the bi-metallic thermo-
stat. In this type of control, two strips of dissimilar metals are bonded
together, such that as the temperature changes, the two metals expand or
contract at different rates. These changes cause the strips to bend, mak-
ing contact and completing or breaking a circuit to control the bunk HVAC
unit. The bi-metallic control needs good airflow through the control panel
in order to react.
The electronic controls for sleeper units have a sensor (or thermistor)
which will detect temperature changes. This sensor is very small and can
be unobtrusively mounted on the front of the control panel. This type of
control has a far narrower “dead band,” the temperature change needed
for the control to react. This allows the sleeper box temperature to be
more closely controlled than with a bi-metallic thermostat. The small size
of the sensor mounted on the front of the control panel allows the panel to
be mounted flush with the walls of the sleeper box.
Heater Controls
The following heater controls are discussed in this section:
1.
Active Heater Controls
2.
Vacuum Controls
3.
Passive Heater Controls
1. Active Heater Controls
Let’s look at a typical heater control panel. There are a couple of slide bars
connected to cables or air lines. The blower (or fan) motor control knob is
attached to a four position switch. Figure 5-5 shows the panel connected
to system components. System design and component locations will vary
from one vehicle to another.