NAVY EE-000-BA-MMA-01 0/7053-AC
AIR FORCE TO 35E9-136-21
backup unit remote status terminal board (TB2), bypassing the PRIME UNIT SELECT switch (S 11) on the
backup unit and enablng the backup unit to operate.
After a fault is cleared, momentarily pressing the FAULT RESET switch (S 12) on the air conditioner control
panel will reset the latching relay (K1) to normal operating status
Low Suction Pressure. If the low refrigerant pressure cutout switch (S4) located at the input port to the
compressor senses low pressure, it opens to de-energize the compressor contactor (K1) and to shut down the
compressor (B 1), and it energizes the low pressure fault slave relay (K 12)
This relay (K12) then acts to de-energize the low suction pressure relay (K9), enabling the fault to be
reported at the remote status terminal board (TB2), closes a circuit which causes the LOW SUC PRESSURE
fault indicator (DS7) to light on the control panel; and energizes the latching relay (K 11) to shut down the air
conditioner and enable the backup unit
Dirty Filter If the airflow through the return air filter decreases to a level that causes the airflow filter switch
(S3) to close (usually caused by blockage of the air filter or failure of the evaporator fan motor B2), the dirty
filter slave relay (K13) energizes.
This relay (K13) then acts to de-energize the dirty filter fault relay (K7), enabling the fault to be reported at
the remote status terminal board (TB2), closes a circuit which causes the DIRTY FILTER fault indicator
(DS5) to high on the control panel, and energizes the latching relay (K11) to shut down the air conditioner
and to enable the backup unit
Fan Motor Overheat. If the condenser fan motor (B3) or evaporator fan motor (B2) overheat, internal thermal
switches (S7 or S6) will open to de-energize the condenser fan motor contactor (K3) or evaporator fan motor
contactor (K2) and shut down the respective fan Both thermal switches (S6 and S7) will automatically reset
when the fan motor housing internal temperature decreases within preset limits.
4.20 HEAT FUNCTION. The principles of operation for the air conditioner, operating as the primary unit while in the
HEAT or AUTO mode of operation, are described m the following subparagraphs (see fig. 4-12).
a. AUTO Mode. All the control and fault circuits described under the cooling function in the preceding paragraphs
apply, in addition to those functions listed m the following subparagraphs.
b. HEAT Mode. When the MODE SELECT switch (S 1) is positioned to HEAT, the following items associated with
AUTO mode are disabled
(1) Solenoid valve (L1) is disabled, stopping refrigerant flow to the primary expansion valve (V5).
(2) Solenoid valve (L2) is disabled, stopping refrigerant flow to the liquid quench expansion valve (V6)
operation of the compressor (B1) and the condenser fan motor (B3)
(4) The COOL indicator (DS2) does not light.
If the return air temperature is below the first stage setting of the thermostat (S2) setting, the first stage heater
contactor (K4) will be energized. This contactor (K4) will cause power to be applied to three of the six 750-watt
heating elements (HR1). In addition, power is applied to the HEAT indicator (DS3) on the control panel, causing it
d. Should the return air temperature fall 1-1/in degrees F below the first stage setting. the thermostat (S2) will
enable added heating by energizing the second stage heater contactor (K5). This contactor (K5) will cause power
to be applied to three additional 750-watt heating elements (HR2).