4–1 62-11637
SECTION 4
ENGINE AND TEMPERATURE CONTROL
NOTES
1. If the unit is in an alarm condition, the control system alarm response may override the operation described
herein. If an alarm is displayed in the MessageCenter, refer to the specific alarm description in Section 9 for
“Unit Control” descriptions.
2. With the complex control interactions in use with the APX control system there are many user selected and
preprogrammed software overrides which may change the operation of the unit. Refer to Section 4.10 &
Section 4.11 for complete descriptions of these features.
4.1 INTRODUCTION
This section describes operation of the unit when in
Start-Stop Operation and Continuous Operation.
For a description and flow diagram of the refrigerant
system component interaction while in cooling, refer to
Section 2.12. For a description and flow diagram of the
refrigerant system component interaction while in heat-
ing, refer to Section 2.13.
4.2 SEQUENCE OF OPERATION - ELECTRICAL
With the battery connected (see schematic diagram
Section 10), power is available from the battery
through fuse F7:
• and fuse F1 to the module logic circuit at main
microprocessor module (MM) terminal 1MM−6,
through the stepper valve module (from 1MM−8
to 1SMV−6) and to the display module (from
1SVM−8 to DM−10),
• and fuse F3, PCM−34 and SP−6 to SVM at
2SVM−22 (for operation of the valves),
• and through SP−6 to the engine control unit
(ENCU) at ENCU−22.
Potential power is also established for the starter sole-
noid contactor (SSC) normally open contacts, the
engine preheat transistor (EPHT), fuel heater relay
(FHR) normally open contacts, AutoFresh Air relay
(AFAR) normally open contacts, power enable relay
(PER) normally open contacts (through fuse F5), the
buzzer (B − through fuse F1) and the START/RUN −
OFF switch (SROS).
Once the module logic circuit is powered, the modules
begin to communicate over the controlled area network
(CAN).
The “HI” CAN connectivity is established from the main
microprocessor (1MM−2) through SP−1 to the stepper
valve module (1SVM−5) and from the stepper valve
module (1SVM−2) to the display module (DM−2). The
connectivity also continues from SP−1 to the engine
control unit (ENCU−23).
The “LO” CAN connectivity is established from the
main microprocessor (1MM−4) through SP−4 to the
stepper valve module (1SVM−7) and from the stepper
valve module (1SVM−4) to the display module (DM−6).
The connectivity also continues from SP−4 to the
engine control unit (ENCU−24).
To start the unit, SROS is placed in the START/RUN
position. Power flows from SROS through the J1
jumper and high pressure switch (HPS) to the power
enable relay (PER) coil. Confirmation of power circuits
are established from splice point SP−9 back to the
main microprocessor at 2MM− 35 and SP− 5 to
3MM−16. If either of these circuits is broken, the appro-
priate alarm will be activated.
If conditions are correct for operation, the main micro-
processor will energize PER by providing ground
through PCM16 from 3MM18. Energizing PER closes
its normally open contacts to provide power:
• through fuse F10 to the main microprocessor at
3MM−34 & 3MM−23.
• through fuse F12 for satellite communication
(SATPWR).
• through fuse F11 for the light bar (LB) green LED’s.
• Potential power is also established through fuse
F10 for the AFAR coil & FHR coil, and through
fuse F8 for the fuel level sensor (FLS).
During operation the main microprocessor will com-
plete the potential circuits, by supplying ground, ener-
gizing or de−energize the required components.
Once the SROS is placed in the START/RUN position,
the compressor suction modulating valve (CSMV) and
evaporator expansion valve (EVXV) will open to a pre-
determined position, to equalize system pressure, and
then close (minimum allowed % open) before the unit
starts.
NOTE
The unit will not restart for at least 30 sec-
onds following a shutdown.
4.3 ENGINE CONTROL
Engine control consists of engine start-up and speed
control.
4.3.1 Engine Start-Up Sequence
On command to perform a Start-up the main micropro-
cessor will supply power from 3MM-10 to the fuel pump
(FP) and from 3MM−9 to ENCU-44. This signals the
ENCU that engine operation is required. The control
system will then enter the engine start sequence. During
the start sequence the engine is operated in low speed.
Following start, the refrigeration system will then operate
in the mode(s) required for temperature control.
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