REMOVAL OF HEATER. (Refer to Figure 21-2)
1.  
Ascertain that all heater controls are off.

2.  
Remove the screw in the nose, lower nose cone to gain access to heater.

3.  
Disconnect the heater outlet duct from the heater manifold by removing the attachment screws.

4.  
Remove the clamp from the intake valve control cable and disconnect the control cable from the intake valve.

5.  
Note the hookup of the electrical leads to facilitate reinstallation.  Disconnect the leads from the heater terminal block.

6.  
Disconnect the fuel supply line at the heater by removing the cover of the fuel line connection shroud and disconnecting the line from the solenoid valve.

21-40-00 Page 21-21 Revised: February 28, 2002
7.  
Disconnect the fuel and water drains from the bottom of the heater and allow them to slide down.

8.  
Disconnect the combustion air blower inlet hose from the blower assembly by removing the cotter key and clevis pin at the blower.

9.  
Loosen the clamps from around the heater and remove the heater from the airplane.  The exhaust shroud should remain in the airplane.

10.
With the heater removed, the necessary maintenance may be performed as required.

INSTALLATION OF HEATER. (Refer to Figure 21-2)
1.  
Ascertain that all the heater components are on the heater.  Position the exhaust tube shroud on the tube mounting flange located in the nose section.

2.  
Position the heater over its mounting brackets and ascertain that the exhaust tube extends into the exhaust shroud. Lower the heater to its mounting brackets.  The exhaust tube should extend out the bottom of the nose section.

3.  
Move the heater slightly to obtain the best fit of the exhaust tube shroud and heater.  Place the heater clamps around the heater and mounting bracket flanges and secure.

4.  
Connect the combustion air blower inlet hose to the combustion air blower assembly on the heater and secure in place with the clevis pin and cotter key.

5.  
Connect the fuel and water drain lines to the bottom of the heater.

6.  
Connect the fuel supply line to the heater and cover over the fuel shroud and secure with two screws.

7.  
Attach the intake valve control cable to the intake valve and install the clamp.

8.  
Connect the electrical leads to the heater terminal block on the heater as shown in Figure 21-2.

9.  
Check the operation of the heater.

10.
Lift the nose cone up and secure with appropriate screws.

THIS SPACE INTENTIONALLY BLANK

21-40-00 Page 21-22 Revised: February 28, 2002
1H20
HEATER ELECTRICAL SYSTEM CHECKS.
ELECTRICAL CHECKS.
These tests are listed as an aid in isolating open circuited or inoperative components.
— Note —
The schematic wiring diagrams (Figures 21-7, 21-8 and 21-9) show, in addition to the heater circuitry, the aircraft control circuit.  For the purposes of this manual, the circuitry shown in these illustrations will be utilized to describe voltage checks.
It must be assumed that power, which is furnished through the heater circuit breaker is present at the HEATER SWITCH at all times.  Always check the circuit breaker before performing voltage checks.
Figure 21-7. Wiring Diagram 21-40-00 Page 21-23 Revised: February 28, 2002
Figure 21-8. Primary Power Circuit 
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Page 21-24 
Revised: February 28, 2002 
1H22 

Figure 21-9. Starting Power Circuit VENT BLOWER POWER CIRCUIT CHECK.
1.  With the HEATER SWITCH in the FAN position, voltage (14 volts nominal) should be present at the following locations: (Refer to Figure 21-8)
A.  Terminal No. 6 on the heater terminal strip if the air valve is open.
B.  From terminal No. 6 of the heater terminal strip through the radio noise filter to the ventilating air motor.
C.  Electrical ground circuit for the ventilating air motor is provided from terminal No. 5 of the heater terminal strip. Ventilating air motor is inoperative when the landing gear is up or air valve is closed.
21-40-00 Page 21-25 Revised: February 28, 2002
HEATER POWER CIRCUIT CHECK.
1.  With the HEATER SWITCH in the HEAT position, voltage should be present at the following locations: (Refer to Figure 21-9)
— Note —
Power for the ventilating air blower is the same as described, except that power is now supplied through the HEAT side of the HEATER SWITCH.
A.  Terminal No. 1 of the heater terminal strip if the air valve is open.
B.  From terminal No. 1 of the heater terminal strip through the radio noise filter to the combustion air motor and to terminal No. 1 of the overheat switch.
　
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