PIPER SENECA II SERVICE MANUAL
a. Deicers: The deicers contain special heater wires protected by fabric plies and by oil and abrasion-
resistant rubber. The side of the deicer cemented to the propeller has a dull finish whereas the air
side finish is “glossy.”
Dual element deicers have a separate lead for the inboard and outboard heater and a third lead
which is a common ground. These leads are so marked. An unmarked ground can be identified by
using an ohmmeter across the three possible pairs of leads. One pair will show twice the resistance
of the other pairs. The latter are the “hot” leads and the lead excluded from the pair that shows
twice the resistance of the other pairs is the ground lead.
Single element deicers have only two leads; one input and one ground.
b. Slip Rings, Brushes and Brush Blocks: To transfer electrical power to the rotating deicers, a brush
block assembly is mounted to the engine by means of a bracket and has brushes which are spring-
loaded to press against the revolving slip rings.
c. Timer: The timer is a sealed unit. If found inoperative, it must be replaced as an assembly - no field
repairs are authorized
d. Ammeter: The ammeter is designed for each particular system and it is therefore important that the
correct replacement part number be used if replacement should be required. In the event of low
aircraft battery voltage (very possible in ground checks), the ammeter readings will be lower than at
full voltage. Provided the ammeter needle reads in the shaded range on the scale (full aircraft
voltage), current flow is considered as normal.
e. Switch: The switch-circuit breaker is mounted in the switch and circuit breaker control panel.
14-5. DEICER SYSTEM OPERATIONAL CHECK.
a. Chock the wheels and operate the engine at near takeoff power.
b. Turn deicer system switch ON and observe deicer ammeter for at least two minutes.
c. The ammeter needle must “flicker” approximately every 34 seconds as the step switch of the timer
operates.
d. With engines stopped, turn deicer switch ON and feel deicers on propellers for proper sequence of
heater operation.
e. The starting point is not important but the sequence is vital and must be: Right Outboard, Right
Inboard, Left Outboard, Left Inboard Heaters, in that order.
f. Temperature rise should be noticeable and each heater should warm for about 34 seconds.
g. Local hot spots indicate surface damage of deicer heaters and should be repaired.
14-6. TROUBLESHOOTING.
Troubles peculiar to the deicing system are listed in Table XIV-IV at the end of these instructions, along
with their probable causes and suggested remedies.
XIV - ACCESSORIES AND UTILITIES 01/01/09
3A10
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