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ARMY TM 9-4120-381-14
NAVY EE-000- CA-MMA-010/7053-AC
AIR FORCE TO 35E9-136-31
4-19. AIR CONDITIONER CONTROL - Continued.
e.
Compressor Circuit. Three phase ac power is applied to compressor motor (B2) when contactor (K10) is
energized. The contactor may be energized by cooling thermostat (S14) or by control relay (K18). Contactor
(K9) is wired in parallel with contactor K10, and when energized, applies three phase ac power to condenser
fan motor (B3). Current overloads (K15 thru K17) are integral to contactor (K9). Current overloads (K23. K24,
and S15) are integral to motor (B2). Circuit breaker (CB2) protects compressor crankcase heater.
f.
Time Delay. Time delay relays (K21 thru K22) temporarily disable two fault detection circuits on start-up.
Time delay relay K21 disables evaporator fan failure circuit for 10 seconds to allow the fan to reach normal
operating speed. Time delay relay K22 disables low oil pressure circuit for 60 seconds to allow compressor to
build up oil pressure in the crankcase.
g.
Fault Circuits. Control relays (K1 thru K6) are part of critical fault circuits. If any of five critical faults occurs,
the appropriate relay (K1 thru K5) is energized by the fault-detecting sensor. The relay applies dc power to the
appropriate LED fault indicator and to summary fault relay (K6). These relays remain energized until FAULT
RESET switch (S1 2) is pressed. When energized, K6 interrupts ac power to MODE SELECT SWITCH (S1)
and contactors (K8 thru K11). Loss of ac power causes unit to shutdown heating or cooling operation if a
critical fault occurs. Control relay (K20), when energized, does not cause a complete shutdown of unit
operations. The remote fault signal is generated if K6 or K20 is energized. Control relay K20 will also remain
energized until S12 is pressed. Sensors are provided to automatically shut down the air conditioner as follows:
CRITICAL
SENSOR
CONTROL
FAULT
FAULT
SWITCH
RELAY
INDICATOR
HIGH DISCHARGE
S4
K1
DS3
PRESSURE
LOW SUCTION
S5
K2
DS4
PRESSURE
-
HIGH AIR
S6
K3
DS5
TEMPERATURE
LOW OIL
S7
K4
DS6
PRESSURE
EVAPORATOR FAN
S8
K5
DS7
FAILURE
CONTROL POWER
K19
DS9
4-20. HEATER CONTROL.
a.
The heater section of the air conditioner uses six electric heaters. The heaters are thermostatically controlled
by heating control thermostat (S9) in redundant configuration and (S14) in single configuration.
b.
Single Configuration. When heating is selected by placing MODE SELECT SWITCH (S1) into either the HEAT
or the AUTO position, and the temperature is below the minimum thermostat (S14) setting, the heaters are
activated by energizing heater contactor (K11) and thus closing K11 contactors and applying power to the
heating elements. The elements will remain on as long as the air temperature is below the thermostat (S14)
setting.
c.
Dual Configuration (Remotely Controlled). When heating is selected from a remotely located control panel (air
conditioner MODE SELECT SWITCH in REMOTE), and the temperature is below the minimum heat control
thermostat (S9) setting, the heaters are activated by energizing heater contactor (Kl1) and thus closing K11
contactors and applying power to the heating elements. The heating elements will remain on as long as the air
temperature is below the heat control thermostat (S9) setting.
d.
A safety circuit is provided to ensure that if, for any reason, the heating elements remain on after the thermostat
(S9) or (S14) should have deactivated them, high air temperature switch (S6) will open and activate the fault
circuit (see 4-19 g).
4-34
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