TM 10-5410-228-24
1.15 ELECTRICAL SYSTEM Continued.
When sensor HOLS3 senses extremely low hydraulic fluid level in the reservoir, relay A4K17 energizes and
hydraulic system shuts down. 24 VDC is applied to two DANGER LEVEL indicators (A4DS26 on the Rear
Control Panel, and A17DS3 on the ECV dash). Indicators light red and two audible alarms (A4LS3 on the
rear control panel and A17LS1 on the ECV dash) sound. Pressing an Override switch (A4S11 on Rear
Control Panel or A17S2 on ECV dash) mutes the alarms and lights override indicators (A4DS25 on Rear
Control Panel and A17DS4 on ECV dash). This allows hydraulic functions to continue by energizing A1SV1
or A1SV2 through diode A4D8 (bypassing the open contacts A2 and A3 of relay A4K16 and open contacts A2
and A3 of relay A4K17.
Air circulated through the ECU and hydraulic fluid are sensed for overheat conditions. Air temperature
switch A1TS1 senses the temperature of air as it circulates through the ECU. Hydraulic fluid temperature
switches A1S4/S5 (integral switches), sense the temperature of hydraulic fluid as it circulates through the
hydraulic system.
24 VDC from Heat/Cool circuit breaker A4CB1 is used as main power source for heat and cool function
control. It is applied to ECU Temperature switch A1TS1 through cables 1A4W6 and 1A4A1W1. If air
temperature inside the ECU is above 200 F, A1TS1 opens and 24 VDC application is interrupted. From
A1TS1 24 VDC is applied to Hydraulic Oil Temperature switches A1S4/S5, If the hydraulic fluid
temperature is below 212 F, A1S4 is closed and the 24 VDC is returned back to the Rear Control Panel
through cables 1A4A1W3, 1A4A1W1, and 1A4W6 where it is applied to ESS Mode switch A4S17-A pin 11
(common connection). A4S17-A applies the 24 VDC to the heat or cool control functions as selected.
NOTE
Temperature switch A1S1, located above the heater elements in the ECU, remains closed as
long as air temperature stays below 200 F. If air temperature rises above 200 F, the power
for operating the heat or cool stages is interrupted or will oscillate ON and OFF. The
temperature switch does not impact system operation when system is set for vent mode.
If the hydraulic fluid temperature is higher than 212 F, A1S4 interrupts the 24 VDC to A4S17-A pin 11 and
reroutes it to light Hydraulic Oil High Temperature lamp A4DS10 on the Rear Control Panel. This will
suspend the heat or cool function and allow the system to attempt to cool the hydraulic fluid below 212 F.
When the hydraulic fluid cools to less than 212 F the heat or cool function resumes operation. If the
hydraulic fluid temperature rises above 230 F, A1S5 closes its contacts and 24 VDC from A4CB2 is applied
through A4S17-B and A1S5 to light Hydraulic Oil Overheat lamp A4DS32 and sound A4LS3 audible alarm.
The only way to mute the alarm is to shut the system down by switching the ESS MODE switch A4S17 to
the "OFF" position.
If A4K18 is de-energized (STATIC mode), 24 VDC from A4S17-A pin 11 is also routed through A4K18 closed
contacts D2 and D3 to rib fan switch A4S13 contact 8. This provides the 24 VDC source for RIB FAN
operation and control.
There are two basic CBPS mission profiles, "MOBILE" and "STATIC". The profiles are selectable on Rear
Control Panel using Mission Profile switch A4S8.
a.
MOBILE Mode. When A4S8 is in the "OFF" position, 24 VDC is supplied from A4CB3
through closed A4S8 contacts 8 and 5 to light A4DS11 "MOBILE" lamp and CBPS system operates in the
"MOBILE" profile mode. 24 VDC from A4S8 contact 5 is also supplied through A4TB1 pins 4 and 5,
connected by diode A4D3, to cooling relay A4K11 contact B2 for cooling function control. With A4S8 in the
"OFF" (MOBILE) position, contacts 10 and 7 also close and 24 VDC from A4CB2 through A4S17-B contacts
21 and 22, A4K16 contacts A2 and A3, A4K17 contacts A2 and A3 to A1SV1 through cables 1A4W6,
1A4A1W1 and 1A4A1W3. A ground is supplied to the opposite side of A1SV1's coil through the same cables.
This energizes (opens) A1SV1 while A1SV2 de-energizes (closes) during mobile mode operation reducing
hydraulic fluid flow through the hydraulic system. 24 VDC from A4S8 contact 7 is also applied to coil
contact X1 of relay A4K18, mobile profile relay, during mobile mode operation. Relay A4K18 energizes
during MOBILE mode to switch heat/cool thermostatic control from A4R1 on rear control panel to A18R1 on
the Control Box Assembly.
