Cessna 150M - Fuel Quantity Indicating System; Trouble Shooting

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15
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40
. FUEL QUANTITY INDICATING SYSTEM.
15-41. DESCRIPTION. The magnetic type fuel quan-
tity indicators are used in conjunction with a float-
operated variable-resistance transmitter in each
fuel tank. The full position of float produces a mini-
mum resistance through transmitter, permitting
maximum current flow through the fuel quantity indi-
cator and maximum pointer deflection. As fuel level
is lowered, resistance in transmitter is increased,
producing a decreased current flow through fuel quan-
tity indicator and a smaller pointer deflection.
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15-41A. REMOVAL AND INSTALLATION OF FUEL
QUANTITY TRANSMITTERS.
a. Drain fuel from tank. (Observe precautions in
Section 12.
15-42.
TROUBLE SHOOTING.
b. Remove access plate above fuel tank for access
to transmitter.
c. Disconnect electrical lead and ground strap from
transmitter.
d. Remove screws attaching transmitter and care-
fully work transmitter from tank. DO NOT BEND
FLOAT ARM.
e. Install transmitter by reversing preceding steps,
using new gaskets around opening in fuel tank and
under screw heads.
f. Service fuel tanks. Check for leaks and correct
quantity indication.
NOTE
Ensure transmitter is properly grounded in
accordance with Section 12.
TROUBLE
PROBABLE
CAUSE
REMEDY
FAILURE TO INDICATE.
No power to indicator or trans-
Check fuse and inspect for open
mitter. (Pointer stays below E. )
circuit.
Replace fuse, repair
or replace defective wire.
Grounded wire. (Pointer stays
Check for partial ground between
above F.)
transmitter and gage. Repair or
replace defective wire.
Low voltage.
Check voltage at indicator.
Correct voltage.
Defective indicator.
Substitute known-good indicator.
Replace indicator.
OFF CALIBRATION.
Defective indicator.
Substitute known-good indicator.
Replace indicator.
Defective transmitter.
Substitute known-good transmitter.
Recalibrate or replace.
Low or high voltage.
Check voltage at indicator.
Correct voltage.
STICKY OR SLUGGISH
Defective
indicator.
Substitute known-good indicator.
INDICATOR OPERATION.
Replace indicator.
Low voltage. Check voltage at indicator.
Correct voltag
ERRA TIC READINGS. Loose or broken wiring on Inspect circuit wiring.
indicator or transmitter.
Repair or replace defective wire.
Defective indicator or trans-
Substitute known-good component.
mitter.
Replace indicator or transmitter.
Defective master switch.
Replace switch.
15-16
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