Fuel Control Components - Piper TWIN COMANCHE PA-30 Service Manual

PIPER TWIN COMANCHE SERVICE MANUAL
b. If there is voltage at terminal No. 6 and the combustion air blower does not
run, remove the heater and return it to the shop for installation of a new com-
bustion air blower motor.
c. If there is voltage at terminal No. 6 and the combustion air blower runs,
the trouble is caused by ignition failure or lack of fuel. To differentiate between
these possibilities,
check voltage at terminal No. 7 of the terminal strip. Loss
of voltage at this point will indicate a defective flame detector switch.
d. If there is voltage at terminal No. 7, turn off the heater switchand discon-
nect the igniter wire from terminal No. 7. Connect anammeter in series between
terminal No. 7 and the igniter wire, then turn on the heater switch. The igniter
should draw approximately 10 amperes.
If there is no current draw, either the
igniter or preheat resistor is defective.
If current draw is normal and there is
voltage at terminal 4A of the relay, it can be assumed that the fuel control valve
shut-off solenoid is defective and the valve must be replaced.
13-38. RUNNING CIRCUIT CHECK. If the heater starts properly, burns for a
short time and then goes out, or develops some other type of malfunction, it can
be assumed that the starting circuit is operating properly and the difficulty is in
the heater control system. The elements which affect heater operation, after
starting, are as follows:
a. Starting safety devices.
b. Fuel control components.
c. The combustion air supply.
13-39. STARTING SAFETY DEVICES. Failure of the flame detector switch to
transfer will be indicated byfailure of the ventilating air blower to start after the
heater has burned for a short time. The fuel safety valve will shut off fuel after
about two minutes, but the igniter will continue to be energized and may burn out
before the condition is detected, since it is not designed for continuous operation.
In all cases where the heater ignites normally and then goes out, it will be
necessary to differentiate between the flame detector switch and the safety valve.
First, reset the flame detector switch as directed in Paragraph 13-29, prime the
safety valve, and make another trial start. If the heater goes out again, check
wiring from the heater terminal strip to the safety valve and then replace the
flame detector switch if no defect is found in the wire. If the valve primes when
the heater switch is in the PRIME position but fails to prime automatically when
the heater is burning, the defect will be found in the wiring between the safety
valve and terminal strip, or between the terminal strip and relay on heaters so
equipped.
If the heater burns for less than one minute and then goes out, the
safety valve is not holding an adequate charge of fuel and must be replaced.
HEATING AND VENTILATING
Issued: 12/29/72
4 B9