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A.  Open LEFT AUTO TEMP CONTROL circuit breaker on load control center circuit breaker panel P6-4.
B.  Unfasten and remove padded ceiling panel to gain access to temperature sensor.
C.  Peel open insulation blanket around temperature sensor.
D.  Disconnect electrical connector from temperature sensor (Fig. 401).
E.  Remove two screws attaching sensor to sensor bracket and remove sensor.
3.  Install Control Cabin Temperature Sensor
A.  Install sensor electrical connector.
B.  Position temperature sensor to bracket and secure with two fasteners.
C.  Open OVERHEAT circuit breaker (P6), remove limit switch electrical connector from left pack valve, then close OVERHEAT circuit breaker.
NOTE:  If airplane pneumatic system is pressurized disregard C.
D.  Close circuit breaker opened in 2.A. and check that all other air conditioning system circuit breakers are closed.
E.  Provide electrical power.
F.  Position L PACK switch to ON.
G.  Position control cabin temperature selector to an AUTO position which will drive the mix valve to the cold position then switch selector to OFF.
NOTE:  If cabin temperature is below approximately 65°F (18.3°C) it will be necessary to provide warm air to sensor.
H.  Hold control cabin temperature selector to MANUAL WARM as required to reposition valve from full cold.
I.  Return temperature selector to position selected in G. and check that mix valve returns to full cold.
J.  Hold temperature selector to MANUAL WARM and check that valve moves toward WARM, then return selector to OFF.
K.  If connector was removed from pack valve limit switch in C., open OVERHEAT circuit breaker, install connector, then close circuit breaker and check that mix valve drives to COLD.
L.  Position L PACK switch to OFF.
M.  Seal insulation blanket by pressing open ends together.
N.  Install ceiling panel.
O.  Remove electrical power if no longer required.
Aug 15/80 21-61-61 Page 401 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

Control Cabin Temperature Sensor Installation  504 
21-61-61  Figure 401  Aug 15/68 
Page 402 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

AIR MIX VALVE POSITION INDICATOR CONTROL UNIT - DESCRIPTION AND OPERATION
1.  General
A.  The position indicator control unit (printed circuit card Al located in P5-17 module) provides regulated voltage and circuit adjustment for position indicators used in the temperature control system. See figure 1.
B.  Power to the control unit is from 28 volt dc bus No. 2 on load control center P6-4.
C.  Regulated current then passes from the control unit to two different position transmitters. Each transmitter is mechanically linked to a valve so that as the valve moves the resistance of the transmitter in the circuit to the position indicator varies. As the resistance varies, so does current, and a corresponding change is induced in the position indicator. A zener diode between power and ground prevents a fluctuating power source from affecting position indication.
D.  The position transmitters (potentiometers) driven by the mix valves provides a voltage proportional to the mix valve position and is sent back to the P5-17 module. The printed circuit card Al in the module contains calibration for this voltage. This voltage is registered on the appropriate mix valve position indicator. The indicators are calibrated by positioning the mix valve transmitter on the mix valve and adjusting the potentiometers in the P5-17 module.
E.  The adjustable potentiometers are numbered R2 and R3 and provide adjustment for indicator pointer sweep of passenger and control cabin mix valves.
F.  The P5-17 module is located in the forward overhead panel. Refer to Position Indicator Control Unit Adjustment/Test for location of adjusting screws.
501 
Aug 15/69  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-61-71 Page 1 

Air Mix Valve Position Indicator Control - Schematic  501 
21-61-71Page 2   Figure 1 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Aug 15/69 

AIR MIX VALVE POSITION INDICATOR CONTROL UNIT - ADJUSTMENT/TEST
1. General
A.  The position indicator control unit is the key link between position indicators and valve position transmitters. Whether a valve, indicator, or a control unit is being replaced, a check should be made to determine that valve position and indicator reading are the same.
B.  There are two variable resistance potentiometers to be adjusted during maintenance. The potentiometers, numbered R2 and R3, are to be adjusted in conjunction with the valve transmitter. (See figure 501.) Transmitter adjustment is typical for each valve.
　
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