21.
Slide the ventilating air blower motor out of the blower housing with the motor bracket assembly and blower wheel attached. Loosen the set screw in the blower wheel and slide it off the end of the motor shaft. Then remove the motor bracket assembly, fasteners and ground bracket.
22.
Remove the screw and lock washer to free the capacitor assembly (18) with attached leads.
DISASSEMBLY OF COMBUSTION AIR BLOWER ASSEMBLY. (Refer to Figure 21-19)
1.
Remove the combustion air blower inlet adapter by removing the screw.
2.
Remove screws; then separate the outer housing from the inner housing and free the motor leads and capacitor from the inner housing.
3.
Loosen the set screw in the blower wheel and slide it off the motor shaft.
4.
Remove the two hex nuts, lock washers and flat washers and slide the inner housing off the motor through bolts. The spacer will drop out.
5.
Install new motor brushes. If the motor commutator is badly worn or if the motor is defective in any respect, it must be replaced.
CLEANING OF HEATER COMPONENTS. (Refer to Figure 21-18.)
— CAUTION —
DO NOT ATTEMPT TO BUFF OR SCRAPE OFF ANY DEPOSITS ON THE FACE OF THE SPRAY NOZZLE. THE FACE OF THE NOZZLE IS VERY SUSCEPTIBLE TO DAMAGE FROM MISHANDLING. CAREFULLY REPEAT CLEANING PROCESS USING ONLY A BRISTLE BRUSH AND REPEATED APPLICATIONS OF SOLVENT TO LOOSEN ANY STUBBORN DEPOSITS.
21-40-00 Page 21-39 Revised: February 28, 2002
21-40-00 Page 21-40 Revised: February 28, 2002
1I14
1.
Clean individual metal parts (except those parts containing switches and electrical wiring) and the combustion tube assembly by immersing them in dry-cleaning solvent, such as Stoddard solvent (Federal Specification P-D-680). A bristle brush should be used to assist the cleaning process if foreign accumulations are stubborn to remove.
2.
Use compressed air or lintless cloth to dry the parts, unless sufficient time is available for them to air dry.
3.
Wipe electrical components with a clean, dry cloth. If foreign material is difficult to remove, moisten the cloth in carbon tetrachloride or electrical contact cleaner and clean all exterior surfaces thoroughly.
CLEANING AND INSPECTING THE COMBUSTION TUBE ASSEMBLY. (Refer to Figure 21-18)
1. Slight scaling and discoloration of the combustion tube assembly is a normal condition for units that have been in service up to 500 airplane hours. The slight scaling condition will appear to be mottled and a small accumulation of blue-gray powder may be present on the surface in certain areas. This condition does not require replacement of the combustion tube assembly unless severe overheating has produced soft spots in the metal.
— Note —
This assembly should be inspected prior to cleaning in order to prevent the removal of visible evidences of damage.
2.
Look inside the exhaust outlet to determine if the combustion tube appears to be heavily scaled or mottled. Deformation is more difficult to detect visually but can usually be observed by looking straight through the combustion tube assembly and sighting along the outer surface of the inner combustion tube. An assembly that has been obviously deformed should be replaced. Slight deformation will not affect heater operation unless it is extensive and localized enough to reduce the flow of ventilating air through the heater more than 10 percent. Inspect the sensing tube for clogging. If it is clogged, it must be cleaned. Disconnect at switch and clean tube by blowing air through it. If combustion by product residue has collected in the exhaust end of the tube, it may be necessary to clean the tube with a wire.
3.
The combustion tube assembly may be cleaned by either of two methods:
A. One method is to soak the combustion tube assembly overnight in a solution of Kelite No. L23S cleaning solution (1 to 12 parts by volume). The solution should be maintained at a temperature of between 190° F and 210° F. After soaking overnight, rinse the combustion tube assembly thoroughly in water to remove all traces of the Oakite solution. In order to reach all areas of the combustion tube assembly, it is advisable to let it stand in the rinsing water for as long as 1/2 hour while occasionally agitating it to circulate the water. All openings should be left open during this operation. Be sure to dry the combustion tube assembly thoroughly after cleaning by blowing with shop air.
B. A second method of cleaning is what is commonly known as hand "tumbling." Insert shot or other metallic particles through the exhaust outlet opening; then close all openings and shake the combustion tube assembly vigorously while rotating it and changing from end-to-end frequently. Be sure to pour out all of the particles and loosened material; then with all openings uncovered, direct a stream of compressed air into the combustion tube assembly from first one opening, then the other. Make sure all loose material is removed.
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