Piper SENECA II Service Manual page 727

PIPER SENECA II SERVICE MANUAL
NOTE
The motor checks described above should be made without the
blower housing attached, for both the ventilating air and
combustion air motors.
b. Test the combustion tube assembly (7) for leaks as follows:
I.
Fashion a scaling plate from approximately I/ 8 inch thick flat stock to seal the combustion
head opening in the combustion tube assembly. (Refer to Figure 13-16.) Use a rubber gasket under the
plate and attach the plate with six screws.
2. Make up seals for all remaining openings, except the one used to connect the air pressure
source. (Refer to Figure 13-16.) 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.
3. 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.)
4. 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.
5. 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.
c. Test the combustion air pressure switch as follows:
I. Connect an adjustable air pressure line that can be controlled in a range of zero to 5.0 psi
(maximum) of water to the switch opening with a water manometer and needle valve in the line ahead of
switch. Switch must be tested in 45 degree position as shown in Figure 13-17.
2. Connect an ohmmeter across the switch terminals to determine the exact instant of switch
closing.
3. Apply air pressure allowing it to build up very slowly from zero. The switch contacts should
close at 0.5
±
0.1 inches of water which will be indicated on the manometer.
NOTE
The switch cover has a differential pressure tap and this opening
must be left open to atmosphere during test.
4. Make several trials to insure switch reliability. Be sure to increase and decrease the air pressure
slowly in order to produce accurate indications.
5. If an adjustment is required, rotate the adjusting screw clockwise to increase settings and
counterclockwise to decrease settings.
d. Test the fuel line and fuel line shroud tube for leaks as follows:
I. Using filtered compressed air, apply 20 psi to the shroud drain port located on the surface near
the threaded nozzle cavity.
2. Immerse the fuel feed and nozzle holder assembly in clean water with the fuel inlet and nozzle
cavity left open.
Revised: 12/08/83
2K20
HEATING AND VENTILATING SYSTEM