The output of the TQG and input AC power to electrical heater stages are both connected to the common side
of A4S1-A. Anytime the TQG is connected to the LMS and its output transferred to the LMS, the 3 phases of
208 VAC are individually supplied to separate sections of circuit beakers A4CB5 through A4CB8 regardless
of POWER MODE selector position.
Four relays, A4K1 through A4K4, and four switches, A4S2 through A4S5, control the application of AC
power from circuit breakers A4CB5 through A4CB8 to the four heater elements. Each of the relay coils are
grounded through Temperature Control Unit, A4TCU. The TCU decides when to apply ground to energize
the selected heater stage as a result of comparing actual air temperature from thermistor A1RT1 and
desired air temperature from A4R1. A heater stage is selected when its corresponding switch is positioned
to ON. For example, heater stage one is selected by pressing A4S2 to ON. This applies 24 VDC from A4S17-
A pins 11 and 12, HEAT selected, to A4S1-B pin 4. With EXT selected, the 24VDC is applied through A4K6
normally closed contacts 13 and 14, NBC OFF, through A4S2 contacts 1 and 8 to the X1 coil connection of
Re-circulation fan circuit control relay A4K6 will be energized under NBC conditions when
NBC switch is pressed or chemical sensor connected to A9J2 senses contaminants and causes
chemical sense relay A4K7 to energize.
Electrical heaters are disabled in NBC mode when powering the CBPS on EXTERNAL power because relay
A4K6 is energized. The Temperature Control Unit provides a ground to X2 coil connection of A4K1 when
actual air temperature is less than the desired setting on A4R1 energizing A4K1. This closes A4K1 contacts
B1 to B2 and C1 to C2 applying AC power to the heater stage 1 element. While relay A4K1 is energized,
HEATER ON lamp A4DS1 is ON. As soon as the actual air temperature reaches the desired temperature
setting, the Temperature Control Unit disconnects ground to relay A4K1 and it de-energizes. HEATER ON
lamp A4DS1 turns OFF and AC power is disconnected from heater stage 1 element. Circuitry for all four
stages of electrical heat operate the same way.
Voltage regulator A4VR1 is mounted on the Temperature Control Unit. A4VR1 provides regulated 24 VDC
for the switching operations in the Rib Pressure gage A4PG2 and NBC Differential Pressure gage A4PG1.
24 VDC from A4CB2 is applied through A4S17-C, ESS Mode switch to A4VR1 pin 1. A4VR1's output at pin
2 is applied to pin A on A4PG1 and A4PG2. This is the only application of regulated 24 VDC.
Three Hydraulic Oil Level Sensors (HOLS), HOLS1, HOLS2, and HOLS3 are mounted on the hydraulic
reservoir. HOLS1 is higher on the reservoir than HOLS2 and HOLS3. HOLS3 is positioned near the bottom
of the reservoir and HOLS2 is positioned between HOLS1 and HOLS3. Together, HOLS1 and HOLS2 are
used to sense a CAUTIONARY level of hydraulic fluid. HOLS3 is used to sense an extremely low level of
When sensor HOLS1 senses low hydraulic fluid level in the reservoir, 24 VDC is applied to time delay relay
A4TD1. If sensor HOLS2 senses low hydraulic fluid in the reservoir, 30 seconds or less after A4TD1 is
activated, relay A4K16 energizes. This opens the electrical path keeping A1SV1 (in MOBILE mode) or
A1SV2 (in STATIC mode) energized (open) and the hydraulic system shuts down. 24 VDC is applied to two
CAUTION fluid level indicators (A4DS19 on the Rear Control Panel and A17DS1 on the ECV dash).
Indicators light yellow. Pressing an Override switch (A4S12 on the Rear Control Panel or A17S1 on the
ECV dash) lights override indicators (A4DS18 on Rear Control Panel and A17DS2 on the ECV dash) and
allows hydraulic functions to continue by energizing A1SV1 or A1SV2 through diode A4D7 (bypassing the
open contacts A2 and A3 of relay A4K16.
Operating the CBPS system with extremely low hydraulic fluid level in the reservoir could
cause extreme damage to hydraulic equipment. The CBPS system should be operated only
during emergency situation preventing death to personnel when extremely low hydraulic
fluid level exists.