AUXILIARY POWER UNIT (APU) CONTROL BOX
APU START SWITCH (1). A three-position GLOW/OFF/START switch used to provide power to the APU for electric
starting and battery charging. In the GLOW position (momentary), the APU glow plug warms and prepares the APU for
starting. In the OFF position, the APU charging circuit is disabled. This switch will not shut off the APU. In the START
position (momentary) the starter is engaged.
On APU with APU engine serial number 504697 and subsequent, the glow plug
indicator is changed from a glow-type indicator to a lamp driven by a timer.
GLOW PLUG INDICATOR (GLOW TYPE) (2). Illuminates when the APU START SWITCH is placed and held in the
GLOW position. The indicator element glows red when the glow plug conductor has become warm enough to assist in
starting the APU.
GLOW PLUG INDICATOR (LAMP) (2.1). Illuminates when the APU START SWITCH is placed and held in the GLOW
position. Extinguishes five seconds later to indicate that the glow plug is warm enough to assist in starting the APU.
THROTTLE CONTROL (3). A push/pull cable controller that manually adjusts the speed of the APU. To increase APU
speed, press center knob and pull outward on the THROTTLE CONTROL. Fine adjustments can be made by turning
THROTTLE CONTROL clockwise (to increase) or counterclockwise (to decrease). To decrease speed, push in
THROTTLE CONTROL. The THROTTLE CONTROL is used to shut down the APU by pushing in THROTTLE
OIL PRESSURE INDICATOR (4). Illuminates when the oil in the APU has not reached normal operating pressure. Once
engine operating oil pressure has been reached, the light will go out. If the oil pressure indicator does not go out within 15
seconds, a malfunction in the engine is indicated.
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