TEMPERATURE CONTROL - TROUBLE SHOOTING
1.  General
A.  Temperature control trouble shooting provides a method for isolating faulty regulating components of automatic temperature control and failures or malfunctions in the manual temperature control system.
B.  Each component used during manual control is also used during automatic control. It is practical to check for problems in the manual system, therefore, before checking the automatic system.
C.  Trouble lights and a temperature indication selector system on the overhead panel provides assistance in trouble shooting the temperature control system. For example, the mix valve, whose position is set by temperature control, governs cabin air temperature. The 190-degree duct overheat thermal switch cuts out temperature control and drives the valve to full cold when a duct overheat condition exists. Should the thermal switch fail closed, temperature control will be lost. At the same time the duct overheat light will come on. Since the duct overheat switch and the supply duct temperature bulb are located in the same duct a supply duct temperature selection when the overheat light comes on will confirm that a duct overheat condition exists or will call attention to a faulty duct overheat circuit.
D.  Lack of temperature control may be caused by malfunctions in the mix valve, duct overheat relay, pack overheat relays, or in either of the relay circuits as well as in the automatic temperature control regulating components. Accurate cabin temperature changes may not be provided by the cabin temperature sensor and bulb if airflow is restricted by an excessively dirty air grille or duct and outlet tubing.
E.  Trouble shooting, therefore, consists of two steps. First check operation of manual temperature control then check the automatic system. If it is determined by watching airplane instruments that manual control is functioning properly only the regulating portion of automatic control need be checked.
2.  Equipment and Materials
A.  Ohmmeter
CAUTION:  AN OHMMETER CONTINUITY CHECK WILL DAMAGE THE FOLLOWING TEMPERATURE SENSORS BEYOND REPAIR.
(1)  
Cabin Temperature Sensor

(2)  
Passenger Cabin Duct Anticipator

(3)  
Passenger Cabin Duct Limit Sensor

(4)  
Control Cabin Duct Anticipator

(5)  
Control Cabin Duct Limit Sensor

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3.  Prepare to Trouble Shoot Temperature Control
A.  Provide electrical power.
B.  Supply pneumatic power.
C.  Check that all air conditioning circuit breakers are in (closed).
D.  Check that following circuit breakers on panel P6 are closed.
(1)  
MASTER CAUTION (all except FUEL, if installed)

(2)  
INDICATOR LTS, MASTER DIM BUS (9 places)

(3)  
DIM & TEST (1 place)

E.  Move AIR TEMP selector to PASS CABIN, then SUPPLY DUCT positions and check that readings on temperature indicator are approximately the same.
F.  Move R PACK (L PACK) switch to ON.
G.  Check that PACK TRIP OFF and DUCT OVERHEAT lights are off and press-to-test to assure proper light operation.
H.  Move temperature selector to MANUAL WARM and check that mix valve moves toward warm by observing mix valve position indicator.
I.  If mix valve moves to warm, move selector to MANUAL COOL and check that valve moves back to full cold. If mix valve does not move in response to selector setting, check per trouble shooting chart.
J.  If mix valve moves in response to manual temperature selection, or if, after a difficulty has been corrected in manual temperature control system, automatic control still doesn't operate correctly, trouble shoot automatic temperature control system.
4.  Trouble Shooting Automatic Temperature Control System
A.  Provide electrical power and perform check per instructions on face of controller.
5.  Trouble Shooting Chart
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K39461
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CONTINUED FROM PRECEDING PAGE CONTINUED FROM PRECEDING PAGE TEMPERATURE CONTROL SYSTEM - ADJUSTMENT/TEST

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