RJ150-30 / Operations and Maintenance Manual
Mobile Aircraft Air Conditioner
Trailer Mounted, Cool Mode Only
______________________________________________________________________________
JANUARY 20, 2004
SECTION 1 - 1
PAGE 21
(6) Air Flow Switch:
The Air Flow Switch (AFS) is mounted on the evaporator housing and
senses the air pressure from the blower. The AFS is normally open (NO)
and ensures adequate airflow is available to support heating and cooling
operations and serves as an interconnect for energizing the compressor or
heat stages. If airflow is lost or falls below the AFS pressure setpoint, the
switch opens and disables heating or cooling circuits. Once adequate
airflow is re-established, the PCA functions are once again enabled.
4. PRE-CONDITIONED AIR CONTROLS:
The unit pre-conditioned air (PCA) cool system controls are set up and tested at
the factory and should not require field adjustments under normal operating
conditions. If adjustments are required, refer to Section 2-4, Adjustments and
Tests. Air conditioner cooling and heating controls are located in the Electrical
Controls Box. (See Figure 7)
A. Cooling Air Flow Volume:
The cooling airflow rate is controlled by the cooling damper control
potentiometer (P1) and is factory set to 70% open (100% = fully open). This
setting may be adjusted as required by local environmental conditions by
setting the cooling damper control potentiometer (P1) to the desired setting.
(See Figure 7) Generally, lowering the setting (i.e., closing the damper)
results in cooler air, but may also result in loss of adequate airflow pressure
across the Air Flow Switch (AFS). Additionally, a reduced airflow may result
in system "icing" and loss of compressor efficiency.
NOTE
Adjusting the cooling air flow rate potentiometer (P1) will affect the cooling
performance of the unit. The normal operating range for P1 is 50-80% open.
The factory setting (70% open) is highly recommended to provide optimal
cooling efficiency.
B. Refrigeration System Defrost Cycle:
The refrigeration system controls include a defrost time delay relay (TDR-1) to
ensure efficient sustained cooling system operation. (See Figure 7) The
defrost timer includes a defrost cycle timer (upper dial) which controls the
frequency of the defrost cycle. This timer is normally set for a defrost cycle to
occur every hour of operation. The defrost cycle duration timer (lower dial)
controls the length of each defrost cycle and is normally set for 1-1/2 minutes.
During the defrost cycle, TDR-1 removes power from the contactor (MC2) and
shuts down the compressor motor(s). The blower motor (M1) continues to
operate during the defrost cycle and will force ambient air over the evaporator
