2.
Inspect all wires and wiring harnesses for damage to insulation, damaged terminals, chafed or cracked insulation and broken plastic bands. Individual wires can be replaced by making up new wires from 16 AWG stock and cut to correct length. It is advisable to use an acceptable crimping tool for installing terminals rather than solder for all heater wiring connections. If wiring harness damage is visible, the entire harness assembly should be replaced. If only one or more wires are damaged, cut the cable ties, make up new wires, install them in the harnesses and restore all cable ties and clamps. If heater controls were operating properly at the time of removal, reinstall them.
3.
Inspect all hard parts consisting of bolts, screws, nuts, washers and lock washers. Replace damaged parts.
4.
The combustion air pressure switch must respond to delicate pressure changes and should always be checked and/or replaced at overhaul. (Refer to Figure 21-17)
5.
Replace the vibrator in the ignition unit at each overhaul.
6.
Inspect the ignition assembly (refer to Figure 21-18) for dented case, loose or damaged primary terminal insulator and broken or obviously damaged high voltage lead. Give particular attention to the condition of the spring connector at the end of the lead. If the spring is burned off, visibly eroded or carbon tracked, the ignition assembly should be replaced.
— Note —
Do not attempt a field repair of the ignition unit, as it is a sealed assembly.
7.
Inspect the terminal strip for distortion and cracks and replace it if either condition exists.
8.
Inspect radio/noise filters for short circuits by checking from either terminal to ground with an ohmmeter. An open circuit reading should be obtained.
9.
Inspect the spray nozzle with a magnifying glass for any obstructions in the nozzle orifice and any sign of damage to the slight conical protrusion at the nozzle tip. Use compressed air to remove obstructions and re-examine the orifice to make sure it is open. Exercise care when handling the nozzle to avoid pressing or rapping on the tip face. Do not buff or scrape off deposits on the tip face. After cleaning, it is advisable to store the nozzle in a polyethylene bag until ready for reassembly.
10.
Replace the nozzle at overhaul.
— Note —
The nozzle can be spray tested by installing it in the holder and connecting the fuel tube to a 7 psi fuel pressure source. The conical angle spray pattern should be even and dispersed the same in all directions. Exercise caution to keep atomized fuel away from fire.
11. Inspect the nozzle holder assembly for damaged threads at the fuel-tube fitting and for crimped or cracked fuel line or distorted housing. Check the solenoid for continuity by connecting across each wire lead with an ohmmeter. A reading of between 15 to 40 ohms should be obtained at room temperature. If not within these limits, the solenoid should be replaced.
21-40-00 Page 21-42 Revised: February 28, 2002
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12.
Remove the brushes, one at a time, from the ventilating air blower motor by removing the brush cap and carefully withdrawing the brush from its guide. Remove foreign material from the brush guide and commutator with a stream of filtered compressed air. Check for brush wear. Inspect the commutator for grooved brush track, pitting or burning. The commutator surface should be smooth and medium brown in color. Replace the motor if the commutator or other parts show damage.
13.
Inspect the combustion air blower motor as described in the preceding step.
14.
Inspect the blower wheel for broken or bent vanes and replace it for either condition.
TESTING.
The following tests should be performed as outlined in the succeeding paragraphs:
1. Check ventilating air and combustion air motors for correct RPM and current draw:
A. Connect motor to 12 volt DC power supply. Rotation should be counterclockwise when viewed from the shaft end.
B. Both motors should rotate at approximately 7500 RPM at rated voltage. Current draw is approximately five amperes.
C. If current draw is excessive or if speed is too low, replace the brushes. Recheck both current draw and RPM after brushes are properly run in.
D. If after replacing brushes operation is still unsatisfactory, replace the motor.
— Note —
The motor checks described above should be made without the blower housing attached, for both the ventilating air and combustion air motors.
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