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Troubleshooting Seneca prop de-icing

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paul_sherry

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Just some guidance and thoughts about where to go looking....

Aircraft - PA34-220T Seneca V with 3 blade prop.

On recent flight the prop de-ice seemed to be messing about a bit. Ammeter showing normal on one side (blue band), slightly low on the other - maybe 2-3 amps low. Checked on the ground and all 6 blades getting warm so thought I would watch and wait. Then a flight where switched on prop de-ice. One side showing normal amps, the other showing nothing. I think the 1950's era Goodrich 'clockwork' timed switch is working ok as every 30 seconds or so the ammeter needle goes to normal range then 30 secs later it drops to zero.

So my current thinking is that the timer switch is (probably) working ok and I checked all three blades before it failed - all seemed working. Which to me means the fail point is likely downstream of the timer, but upstream of the three individual heating pads. Because if it was one heating pad then I would be seeing 10 amps rather than 15 (5 amps per pad I seem to recall)

Most likely candidate might be the brush block where the volts/amps gets from the 'fixed' bits to the 'spinning' bits (slip rings).

I haven't had a chance to get the engine cover off yet but I thought I would post here and see what everyone thinks.

Thanks

Paul
 

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