TM 10-5410-228-24
1.15 ELECTRICAL SYSTEM Continued.
When the NBC FAN switch A4S15/16 is first positioned to "ON", A4PG1 switch contacts H and J are closed
and relay A4K8 energizes. A4K8 contacts A1 and A2 close applying 24 VDC to light NBC PRES LOW lamp
A4DS29 (red), and sound NBC audible alarm A4LS1. Positioning NBC FAN switch A4S15/16 to "ON" also
interrupts the 24VDC path that keeps A1SV6 energized. A1SV6 de-energizes and closes forcing all
hydraulic system fluid flow through the NBC FAN motor increasing its speed to over-pressurize the ABS.
When using INTERNAL power, A1SV9 remains energized (closed) and the recirculation fan remains in
operation. When using EXTERNAL power, A1SV9 de-energizes (opens) and the recirculation fan is shut
down to aid in keeping the NBC FAN turning fast enough to keep the ABS over-pressurized. A4DS29
remains "ON" and the alarm continues sounding until A4PG1 reaches 0.5 iwg (normal). At this point,
A4PG1 switch contacts H and J break contact and relay A4K8 de-energizes opening contacts A1 and A2,
turning "OFF" A4DS9 and audible alarm A4LS1. The audible alarm can be muted by pressing NBC ALARM
switch A4S10 to "ON". While A4S10 is positioned to "ON", the audible alarm is turned "OFF" and the
ALARM MUTE lamp A4DS9 lights (blue). A4PG1 does not have a hi-set point to reduce NBC FAN speed
when over-pressurization is achieved. Over-pressurization is controlled by positioning flaps over holes on
ABS ambulatory and TALP inner and outer doors.
NOTE
When using external power (10 kW TQG), under NBC conditions, cooling capabilities are
locked out. Relay A4K11 de-energizes and keeps Solenoid valve A1SV4 de-energizeD
(CLOSED) to enhance NBC performance.
a. INTERNAL POWER, STATIC Mode, NBC Off. When Cool is selected, A4S17-B pin 17 routes 24
VDC to the coil of 60 second time delay relay A4TD3. A4TD3 energizes after 60 seconds of COOL
operation giving the Air Conditioning function time to build high side refrigerant pressure. HPS1
contacts A and B are closed until high pressure is sensed and route the 24 VDC through relay
A4TD3 closed contacts 1 and 4, and A4S1-B contacts 26 and 25 to the coil of A4K11. A4TCU applies
a ground to A4K11 to energize it when actual air temperature is warmer than referenced by A4R1
(static mode) or A18R1 (mobile mode). When A4K11 is energized its contacts A2 and A1 close and 24
VDC is applied to A1SV4 which reroutes hydraulic fluid through refrigeration compressor motor.
The same 24 VDC is applied to RSV3 to open refrigerant line allowing refrigerant fluid to flow. If
the low pressure side of refrigeration function has not built up low pressure at the end of 60 seconds
of operation, LPS1 contacts A and B apply 24 VDC through A4TD3 closed contacts 8 and 5 to light
REFRIGERANT PRESSURE LOW lamp A4DS6. If low pressure is normal LPS1 changes position
and contacts A and C apply 24 VDC to the coil of A4K11 to keep it energized. If the high side re-
frigerant pressure rises too high HPS1 changes position and contacts A and C apply 24VDC to light
REFRIGERANT PRESSURE HIGH lamp A4DS5. When actual air temperature is less than desired
temperature, A4TCU removes ground from A4K11 and the relay de-energizes shutting down the
cooling function. Operation cycles on and off to keep the temperature in the ABS relatively constant.
If NBC operation is activated when INTERNAL power is used the cooling function operates as stated
above.
b. When EXTERNAL power is used without NBC the cooling function operates as stated above with
one exception. Relay A4K15 energizes and its contacts A2 and A3 open which interrupts the 24 VDC
keeping RSV1 energized. When RSV1 de-energizes, the high rate of cooling changes to a lower rate
(cooling is not as effective). This aids the lower capacity Auxiliary Hydraulic Pump keeping the
remaining portions of the CBPS in operation. Relay A4K15 also energizes when MOBILE mode is
selected to reduce the output of cooling function during MOBILE mode.
If NBC is selected when using EXTERNAL power, the cooling function becomes inoperative since the
24 VDC path to energize cooling relay A4K11 is interrupted.
Applies 24 VDC to light REPL FILTER lamp A4DS21 (red) when return oil differential switch A1DPS1 is
activated.
