PA34 janitrol combustion heater

[aerobat77]

hey!

i,m riding a seneca II for a company and sometimes the heater drives me crazy.

sometimes you switch it on and no warm air comes out during the whole flight. the overtemp warning light is off, fresh air inlet is open, all seems fine, but it does not work...

of course the passengers are not happy with it.

at last leg the whole time it did not work. i tried switching it off and on again inflight, change ram air openenings, nothing.

on the return lag the same- but suddenly the thing inflight kicked in at full power and instant warm air came out .

we said it to our shop but they were not able to find any malfunction, the heater was rebuild one year ago...

any hints?

thanks much !

[411A]

A duff ignitor (or, ignitor box), more than likely.
I would suggest...the cause of the problem be found PDQ, before further flight where the cabin heater is necessary.

[stevef]

I'd be suspicious of one of the following:
1) Combustion pressure switch.
2) Duct switch.
3) Cycling switch.
4) Fuel supply (unlikely).
Easy enough access in a Seneca if I remember rightly.

[rogerg]

I once had a problem like that years ago in an Aztec, however it would work if the gear was down!

[aerobat77]

thanx much guys!

well, it seems we have to bring it back to our shop and tell them that they have to check it again and again until they found the problem. especially the ignitor and ignitor box , further the combustion pressure , duct and cycling switches.

the access to it is indeed very easy in the seneca.

the problem is that one day it works fine, the next it does not work. of course due to murphys law when you are at the shop the heator will work...

i told my boss that on cargo missions we can live with it, but with passengers a heater inop at Fl110 with temperatures below freeze is basicly inaceptable.

[stevef]

Infernal Machines, these combustion heaters. Just as well the pax don't know what's going on behind them. :eek:
My strongest suspicion is that the Combustion Air Pressure Switch is defective. From memory, it's a circular valve about 3" in diameter mounted on top of the heater unit. It measures the differential between inlet and exhaust pressure. I'm a bit rusty but I think if the drop across the diaphragm suggests insufficient airflow, the switch cuts off the fuel supply.
All of the temperature-related switches are easily accessible, so diagnosis by replacement (if you have the spares but not the test equipment) is easy.
It'll be interesting to hear the result.

[mustbeaboeing]

aerobat 77..

With regard to you comment..."I've told my boss that on cargo missions we can live with it, etc etc..."

Maybe worth thinking that one through.....

I presume your location is correct.......Winter coming up. Very cold etc.

Used to fly C404 (Titans) light years ago. They had a similar, possibly same, system you mention.

Heaters would sometimes stop.

Ever seen someone try and reduce power (bring the throttles back) after a couple of hours in an aircraft with no heater.

I realise the Seneca does not have the same range/endurance but it bears thinking about.

[BOAC]

Coked up igniter was the Aztec problem for me - clean it on a turn-round and it was fine.

[aterpster]

BOAC:

Coked up igniter was the Aztec problem for me - clean it on a turn-round and it was fine.

I flew an early Apache a lot when it was fairly new (circa 1959-61). The heater was balky but I always managed to get it to work.

Fortunately, those days were fairly brief.

My recollection, albeit perhaps faulty, is that some of them either caught fire or exploded with aging aircraft so equipped.

[Old Fella]

Janitrol heaters have always been problematic and often, as has been noted, the offending item is nothing more than a fouled ignition plug.

[Oktas8]

Since everyone else has mentioned sensible maintenance actions to take...

If you're stuck with a difficult-to-start heater with all the obvious things replaced, I have had success starting the heater on the ground before it gets cold-soaked airborne. If it won't start on the ground, at least you can make a decision whether to fly without it.

Cheers,
O8

[aerobat77]

ok, we will start with cleaning the ignition plug and see if it helps. when not i will tell the shop to look especially at all switches. in every case i will let you know.

@mustbeaboeing:

you,re right, it maybe a safety issue when you freeze up in the front , regardless if you carry cargo or passengers. but what will you tell the boss? that you will not fly any minute more when the heater is not trustful? the heater is not covered by the MEL...

i think it will be fixed soon, he agrees that its a no go in winter session, and i must say we use especially the seneca in serious conditions, legs of 4 hours are a common business, IFR operated.

we have a turbo seneca and two cheyennes in the company, i fly both types left seat ( commercial we also operate the seneca with two pilots) and its sometimes more a challange than a cheyenne since with the cheyenne you go mostly above the weather and here you deal with things like ice also enroute.

[BOAC]

Memories fade (28 years) but I think the Aztec said 'airborne only'.

Operating in Scotland it was always nice to hear that (not too loud!) 'Pop' as it lit.:)

[Pugilistic Animus]

stills sounds better than the combustion steam boiler EKG describes for the DC-2:\