Piper SEMINOLE PA-44-180, Maintenance Manual

Page: 148 / 881

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.
2. Test the combustion tube assembly for leaks as follows:
A. Fashion a sealing plate from approximately 1/8 inch thick flat stock to seal the combustion head
opening in the combustion tube assembly. (Refer to Figure 21-16) Use a rubber gasket under
the.plate and attach the plate with six screws.
B. Make up seals for all remaining openings, except the one used to connect the air pressure source.
(Refer to Figure 21-16) Use rubber stoppers as shown. The combustion air inlet tube can be sealed
best with a drilled stopper and clamp. Other openings should be sealed with expansion plugs. The
seal used in the exhaust tube should be formed so that it will not deform the air pressure switch tube
which protrudes into the exhaust.
C. Install plugs and caps in all openings except the one to which the combustion air pressure switch is
attached. (Any opening can be used to connect the air pressure source, however, the combustion air
pressure switch opening is usually the most convenient. The drain opening would normally be
considered a second choice.)
D. Connect a regulated air supply to the opening that has not been plugged and apply a pressure of
between three and five psi to the combustion tube assembly.
E. Submerge the combustion tube assembly in water for several minutes while watching for bubbles
which would indicate leaks. No air leakage is permitted from the combustion tube assembly. No
weld or braze repairs are permitted on a combustion tube assembly.
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
2 1 - 4 4 - 0 6
Page 21-37
Revised: May 15, 1989
1G4
PIPER AIRCRAFT