Hello,
Our heater works usually for about 30-45 min in flight. Then it stops. A restart even after a while is without success.
Back on the ground the heater works fine again. The failure cannot be reproduced on ground.
Therefor I run cables from all five switches (cycling-, duct flow-, pressure-, flame sensor- and overheat-switch) to the cockpit to figure out which one of the five switches is responsible for the stop.
But the mastermind plan did not work out. The heater stops but even though on all five switches are 12V. So there are only three possibilities left: Magnetic fuel valve, electric fuel pump or the ignition.
Has anybody a good idea to narrow down the problem which of the three components it might be?
Best regards
Christian

Christian,

What electric fuel pump are you referring to? There isn't one for the heater to my knowledge.

Ja, in our Comanche there is one. The electric fuel pump for the heater is mounted in the nose compartment on the fire wall. It is a magnetic pump which runs continuously as long as the heater switch is on. It only stops pumping when the backpressure is too high to move anymore when the magnetic valve from the heater stops the fuel flow.

Christian,

Was that installed with a field approval or STC? I have never heard of this and Piper did not certify the aircraft with that pump installed on a Janitrol heater.

Kristin,

might be. It was already there when we bought her.
But my problem is that the heater stops after a while and only when up in the air.
Do you have an idea how to check the magnetic fuel valve?

All the best

Christian

Christian,

This is completely novel, so I am just guessing here. It seems however that any test rig you set up to check the fuel pressure while inflight would be more expensive than just replacing the pump in hopes that solves the problem. You can get a PMA unit from McFarlane for relatively little money.

The "magnetic fuel valve" is a solenoid/regulator that should be open to allow fuel to pass when the Right engine fuel pump is running, or electric pump on, and the heater master is on, with the switch to the heat position. You can pull the fuel line to see if you are getting fuel. Assuming that you are, you can pull the spark plug and see if it will spark under those same conditions. (careful of the fuel). If you do not have spark, I suggest that it will be the ignition vibrator. Perhaps, remove and replace the vibrator, amking sure that it is good and tight in the socket.

If you need reference, I can email you the book.

Hope this helps,
larry

Hmmh, we checked this already. Fuel is coming out of the line. The sparkplug works. Blower motor brushes are ok...
On ground verything works fine. Up in the air, everything works fine for 30-45minutes. Then ist stops und it becomes freezing cold All switches (duct flow, cycling, pressure, overheat, flame sensor) are set to go and have +12V.
My main suspect is the fuel pump. I will replace it since I do not know how to check it online

Best guess is your combustion blower is weak and after time especially at altitude it isn't able to maintain the pressure required for the pressure switch to be made and the heater quits. This might be indicative of failing bearings in the motor etc. Like others have said, there should be no aux pump on the heater, it should get its fuel pressure from the right engine. Any time it is running or the right aux pump is running, you should have pressure to the heater.

Zach

Hello Zach,

I agree. The fuel pump which is installed in our nose is an automotive fuel pump you can find in GM or Honda cars. Not only the pump itself but also the way it is installed is absolutely not aircraft like.
But for some reason some of the guys who owned the plane before had obviously problems with the fuel supply to the heater.

The combustion air blower was not suspicious to me since the pressure switch is always engaged when the heater refuses to work any longer. If the blower motor is weak the pressure switch should run into failure and disengage. But I will keep the proposal in mind on my further investigation.

Next step is to take that automotive fuel pump out to see how it works without that piece.

Many thanks

Christian

You have an igniter and a fuel valve. The valve gets clogged up with carbon and fails to spray the fuel correctly. The igniter gets old and weak. The overheat shutoff might be faulty.
It's time for a proper overhaul.
The basic problem is altitude - less oxygen up there, so the heater stops working.
Hartzell Engines owns Janitrol now - be glad that you don't have a Southwind - it just was whacked with a big A.D. If I was you I was call Harold Haskins and ask him what to do - Harold is a good guy and is the biggest Janitrol overhauler in the USA.