Using The Ammeter; Deicer System 50 Hour Inspection - Piper PA-44-180 SEMINOLE Maintenance Manual

USING THE AMMETER.

Whether in flight or during ground testing, the ammeter can be used to indicate the general nature of most
electrical problems. The troubleshooting chart is primarily based on the use of the ammeter and assumes that the
user does understand all normal operating modes of the system.
When troubleshooting, first use the "ammeter test" and "heat test" to determine which
circuits are involved. Use circuit diagram for assistance to check voltages or
continuity.
HELPFUL TIPS.
1. If the ammeter reading drops to one-third normal current, this indicates that one heater circuit is open.
2. Excess current reading on the ammeter always indicates a power lead is shorted to ground. Thus, when
trouble of this nature is found, it is vital that the grounded power lead be located and corrected.
3. A considerable number of timers that have been returned for repair proved to be fully workable when tested.
Accomplish the test described in "Timer Test" before concluding that the timer is defective.
4. Defective wiring in propeller mounted components may be indicated by normal current readings in ground
checkouts (propellers not rotating) but low current with propellers rotating at cruise RPM.
INSPECTION.
50 HOUR INSPECTION.
1. Lock brakes and operate engines at near takeoff power. Turn deicer system switch ON and observe deicer
ammeter for at least two minutes. Ammeter needle must rest within the shaded band, except for a "flicker,"
approximately every 90 seconds, as the step switch of the timer operates. Any movement of the needle
other than the normal 90 second flicker indicates a short or open that must be located and corrected.
2. With engines stopped, turn deicer switch ON and feel deicers on propellers for proper sequence of heater
operation. The deicers should cycle ON for 90 seconds, then OFF for 90 seconds and repeat. Temperature
rise should be noticeable and each heater should warm for about 90 seconds. Local hot spots indicate
surface damage of deicer heaters requiring replacement of deicer.
3. Remove spinner dome and engine cowling. With assistant observing deicer ammeter and with deice r
switch ON, flex all accessible wiring, particularly the deicer wire harness, leads from slip ring assembly,
and the firewall electrical connectors and their wiring. Any movement of the ammeter needle other than the
"90 second flicker" of cycling indicates a short or open that must be located and corrected.
PIPER AIRCRAFT
PA - 4 4 - 1 8 0 / 1 8 0 T
AIRPLANE MAINTENANCE MANUAL
— Note —
2E11
3 0 - 6 5 - 0 1
Page 30-31
Revised: May 15, 1989