Deicersdo not inflate. Pneumaticpressure gaugein green.
Deicers inflate slowly (Inflation time -6 + .5 seconds.)
Systemdoes not achieve operatingpressure. (Leak testshowsno sign.)
Cause
Open circuit breaker.
System connection looseor wire broken.
Timernot functioning.
Deicervalvesnot functioning.
Linesblockedor not connected.
Linespartiallyblockedor notconnectedsecurely.
Deicervalve not functioning.
Systempressure not beingreached.
Deicerpuncture.
Inflationtime inadequate; timer not functioning
properly,solenoid valve
not open for six seconds.
Remedy
Pushcircuitbreakerto reset.
Tightenor repair as required.
Test and replaceif required.
Makeelectricaltest. Check for sticking poppet.Clean.
Blowout lines and inspect connections.Makeair leakage test.
Blowout linesand inspect connections.Makeair leakagetest.
Testor replace as required.
Check pneumatic system performanceto manu-facturersspecifications.
Repairper specification orreplace.
Testandreplaceas required. Cleanor replacevalve.

EFFECTIVITY:

040-999
30-10-00Jan 10/90

PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. Airfoil-DescriptionandOperation(continued)
CHART 1 (Sheet 2 of 2)
FAULT ISOLATION (PNEUMATIC AIRFOIL DEICER SYSTEM)

Fault  Cause  Remedy 
Deicersdeflateslowly.  Pressureregulatorsettoo  Readjustpressure 
low.  regulator. 
Linespartiallyblocked.  Inspectandblowout 
lines. 
Overboardlinefrom  Inspectandblowout 
controlvalvepartially  lines. 
blocked. 
Leakagein system  Leakcheckandcorrect 
plumbing.  leaking. 

EFFECTIVITY: 040-999

Jan
10/90 30-10-00
PIPER AIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL

A. Airfoil -Description and Operation (continued)
1. Operationalcheck.
Check pneumatic deicing system on the ground at least every 100 hours including a visual inspectionof the deicer boots.
With one engine operatingat 80% Ng, turn on deicing system. The pressurewillfluctuateas tubes
inflate and deflate. Checkpneumaticpressuregauge.If pressure is satisfactory, check operation
of deicers for a malfunction andlook for tubes which leak or fail to inflate and deflate properly.
Repeat procedure forother engine.
2. Electricaltest.
With engines off, turn airplane battery switch on.
(a) DeicerValves. Check valves beneath center floorboard aft of Fuselage Station 154.00. Turn system switch on. One valve must actuate immediately for 6 ± 0.5 seconds with an audible click which can be felt if a hand is placed on valve. The other valve must actuate 6 ± 0.5 seconds after the first and remain actuate for 6 + 0.5 seconds. If either valve does not function, follow instructions below:
(1.) Disconnect wires at valve. Attach test light or other suitable test equipment to connector and reactuate system switch. If test equipment does not indicate complete circuit, completethe following checks: (a.) Check circuit from timer to valve connector to ground. (b.) Replace timer (refer to PA-42-720 (Advanced Trainer) Parts Catalog).
(2.) Use an ohmmeter to check valve for an open circuit. If valve circuit is open, replace valve.
3. Pressureleakage test. (Figures 1 and 501)
(a)
Removeappropriate floor panels to gain access to deicer solenoid valves under floor at Fuselage Station 157.00, near center of fuselage.

(b)
Disconnect pressure/vacuum line from outboard boots valve. Connect test apparatus to line (shown in Figure 501).

NOTE: Use only clean and oil-free shop air. Shop air source must be capable of applying at least 18 psig.
(c)
Attachshop air to test apparatus with control valve closed. Adjust regulator until19 psig registerspressuregauge (number 1) ahead of control valve.

(d)
Slowly open control valve to inflate outboardwingdeicer boots.

(e)
Allow system to stabilize and close control valve. With pressuretrapped in system, check pressuregauge (number 2) downstream ofcontrol valve. Ensure leakageratedoes not exceed3 psig per minute.

(1.) If system does not hold required pressure, use soapy water to find leaks. (2.) If connections leak excessively, tighten as much as possible. Replace as necessary. Do not use thread sealants on threaded fittings.
EFFECTIVITY:

040-999
30-10-00
Jan 10/90

PIPER AIRCRAFT PA-42-720 (Advanced Trainer) MAINTENANCE MANUAL
A. Airfoil -Description and Operation (continued)
3. Pressure leakage test. (Figures 1 and 501) (continued)
(f)
Relieve pressure in system by slowly opening fitting at test apparatus.
　
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