6.  
Connect a voltmeter from open side of combustion air pressure switch terminal to ground to determine if the switch is closed, which would be indicated by a full voltage reading on the meter.  If a full voltage reading is not obtained, the combustion air supply is either inadequate or the switch is defective or improperly adjusted. Make necessary corrections.

21-40-00 Page 21-51 Revised: February 28, 2002
7.  
Observe the manometer connected to the ventilating air pressure tap, which should show a reading of 1.1 inches of water (minimum) at rated voltage.

8.  
Observe the manometer connected to the combustion air tube tap, which should show a reading of 1.5 inches of water (minimum) at rated voltage.

9.  
Open the power supply switch and reconnect the terminal lead disconnected in preceding Step 5.

10.
Close the power supply switch and turn on the fuel supply.  The heater should light within five seconds (may require slightly longer for air to be purged from fuel lines on the first trial).

11.
Observe operation of duct switch, which should control heater operation according to the switch setting.

12.
If the duct switch fails to control the temperature according to the setting, place the control lever in high “H” position and notice the control variation.  A high reading of 250°F ±10° should be obtained (reading will vary in different applications).

13.
Connect a jumper across the terminals of the duct switch to make it inoperative and observe action of the cycling switch.  The cycling switch should cycle to control the outlet air temperature at approximately 250°F (nominal). This is a function of ambient temperature and airflow conditions.  If operation is within a range of 190°F to 290°F, the switch is operating normally.  If the switch is out of range, it can be reset in the same manner as described for the duct switch, except that no control lever or indicator stop are used. If adjustment fails to restore proper temperature range, replace the switch.

14.
With duct switch still jumped, place a jumper across the cycling switch terminals to check operation of the overheat switch.  Block the ventilating air outlet and notice if the overheat switch shuts off the heater. It should open at between 300°F and 400°F.  (This is also a function of ambient temperature and airflow.) After the switch shuts off, remove ventilating air restriction; remove jumpers from cycling and duct switches and press firmly on the overheat switch reset button until it “clicks.” The heater should light and operate.

15.
Shut down the heater and check all components visually to make sure no damage has occurred to any of them.

16.
Remove heater and other components from the test setup and install it in the airplane.

INSPECTION OF FUEL NOZZLE ORIFICE. (Refer to Figure 21-18)
1.  
Loosen the four screws and rotate the blower and motor housing to disengage the ventilating air blower from the end of the heater jacket.  It is not necessary to disconnect the electrical connections to remove the nozzle.

2.  
Remove the fuel shroud cover by removing the screws.  Remove solenoid and elbow.

3.  
Reach inside the inlet end of the jacket assembly with a 3/4 inch open-end wrench and, while holding the fuel-tube fitting of the jacket, use a 3/4 inch deep socket to remove the nut, washer and gasket and lower fuel shroud box.

4.  
Remove the two screws and carefully withdraw the nozzle holder and valve assembly from the 
combustion head assembly.

5.  
Carefully unscrew and remove the spray nozzle from the nozzle holder.  Remove the gasket.

6.  
After cleaning the nozzle, reinstall the parts removed in essentially the reverse order from removal.  Be sure to hold the fuel-tube fitting when tightening the nut to avoid damage to the fuel tube.

21-40-00 Page 21-52 Revised: February 28, 2002
1J2

HEATER HOURMETER.
REMOVAL OF HEATER HOURMETER.
1.
Remove the screws which secure the nose cone and lower the nose cone to gain access to the heater. The hourmeter is located on top of the heater, secured to the ignition assembly. (Refer to Figure 21-2.)

2.  
Note the position of the wires on the rear of the hourmeter, then disconnect the wires.

3.  
Remove the screws which secure the mounting clamps to the ignition assembly and remove the 
hourmeter from the aircraft.

INSTALLATION OF HEATER HOURMETER.
1.  
Position clamps on hourmeter as indicated in Figure 21-23.

2.  
Secure first clamp to ignition assembly bracket using screw MS35206-242.
　
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