21-61-0  May 15/79
Page 502
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.

(m)  
Check that indicator on mix valve reads full cold.

(n)  
If the position indicator on the forward overhead panel does not align with either the full hot or full cold index mark, adjust the mix valve position transmitter. Refer to Air Mix Valve Position Indicator Control Unit.

CAUTION:  DO NOT USE OHMMETER FOR CHECKING THE POSITION TRANSMITTER. THE TRANSMITTER IS A SENSITIVE VARIABLE RESISTANCE ELEMENT WHICH WILL BE DAMAGED BEYOND REPAIR IF SUBJECTED TO AN OHMMETER CHECK.
(4)  Test Automatic Control
(a)  General
1)  Testing the automatic temperature control provides a check that the sensing devices in the regulation system, the temperature selector, the temperature regulator, and the mix valve are functioning properly.
2)  The range of cabin temperature selected lies between 65°F (18°C) and 85°F (30 °C). The cabin temperature sensor will be approximately ambient temperature. It is necessary therefore to provide a slightly different method for checking the system when ambient temperature is below 65°F or above 85°F. Step (c) describes the test requirements determined by ambient temperature and assumes that inside the cabin the temperature is approximately ambient.
(b)  Position the mix valve to midposition.
1)  Move the temperature selector knob to manual warm while observing mix valve position on the indicator. When the mix valve reaches approximately its midposition, move the selector knob back to OFF.
2)  When ambient temperature is below 65°F (19°C) apply a controlled heat source to the cabin temperature sensor and set it at approximately 75°F (24°C). When ambient temperature is above 85°F (30°C) apply a controlled cold air source to the cabin temperature sensor until it's temperature is approximately 75°F. If ambient temperature is between 65°F and 85°F proceed with step 3).
NOTE:  The temperature scale in the automatic temperature range of the temperature selector covers 20°F (11.1°C) from 65°F to 85°F and each index mark is 5°F (2.8°C) separated from the adjacent index mark.
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Aug 15/69  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  21-61-0 Page 503 

3)  Move temperature selector knob until pointer is at approximately the same temperature as the temperature of the sensor then make fine adjustment with knob such that mix valve stops its movement.
NOTE: While making fine adjustment observe mix valve position indicator. If reading on indicator shows the mix valve moving toward hot turn the selector knob counterclockwise. If valve is moving toward cold, adjust knob clockwise. The null setting on the selector should be within + 1.5°F (+ 0.83°C) of sensor temperature.
(c)  
Move temperature selector knob counterclockwise from the null position approximately 2°F (1.1°C) and check that the mix valve moves toward COLD.

NOTE:  2°F movement on the selector scale corresponds to just less than half the distance between index marks.

(d)  
Return mix valve to intermediate position per step (b).

(e)  
Move selector clockwise approximately 2°F (1.1°C) and check that the mix valve moves toward HOT.

(f)  
Return mix valve to intermediate position per step (b).

(g)  
Remove the cabin duct temperature limit sensor from the main distribution manifold.

(h)  
Apply heat to the cabin duct temperature limit sensor probe and check that the mix valve drives to full cold.

(i)  
Allow the sensor to cool until it may comfortably be held by bare hand, then reinstall in main distribution manifold.

(j)  
Reposition the mix valve per step (b).

(k)  
Check that when the DUCT OVERHEAT light is pushed, it comes on, and when it is released, it goes out.

(l)  
Remove the 190-degree duct overheat thermal switch from the main distribution manifold.

(m)
Heat the 190-degree duct overheat thermal switch until the DUCT OVERHEAT light and the MASTER CAUTION and AIR COND annunciators comes on.

NOTE:  The 190-degree duct overheat light should come on at a probe temperature of 190 +5°F, (88 +3°C).

(n)  
Check that the mix valve drives to full cold.

(o)  
Depress MASTER CAUTION light (either) and check that both MASTER CAUTION lights and the AIR COND annunciator light on the lightshield go out and the DUCT OVERHEAT light on the overhead panel remains on.

(p)  
Push AIR COND annunciator and check that MASTER CAUTION lights and AIR COND annunciator light come back on.
　
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