Heat vents so hot they'll burn to the touch

[Quint Van Deman]

Fellow Comanche flyers--

I've just been through an engine overhaul, and there's one odd squawk hanging around that I'd like to consult the group on.
Regardless on the position of the master heat selector (next to the door), the air that's flowing through the ducts is so hot that it's making the metal vents (where the heat actually comes out when open) so hot that they will burn if even brushed (almost alarmingly hot). While I have not removed the duct inside the cowling to confirm that the master door real is full closing, the cable is connected and appears to be operating normally. Thus as a starting point, can anyone:
A. Offer if this is unusual, or expected
B. If unusual, offer the first couple of checks

My mechanic seems to think that I never noticed this heat before because all the duct work was so full of holes that it let all of the heat escape. Much of it was replaced during the engine overhaul, and he thinks the system is just holding air better & thus conveying more heat, which might be good in the winter, but it's making everything rather uncomfortable this time of year.

Thanks in advance,

-Quint

[fowlerflaps]

Hi Quint. I also notice the same thing on my PA30C. Both the vents under the panel and along side the front seats get very hot to the touch. On a recent flight back from FL last week I was thinking about this and the possibility of it getting so hot that possibly a fire could start.

Chad

[Zach Grant L1011jock]

Normal, and no fires have been reported due to this!
-Zach

[Quint Van Deman]

[Ray B]

Zack, It's hard to believe the vents were designed to be hot when closed. Are they also used as fresh air vents or just for heat? Ray B

[steen]

Many years ago when I first owned my -30B the heater put out heat as you describe and I flew it a couple years, thinking it was normal.
As I went through the plane, system by system, I had time to thoroughly check out the heater and learned that it was cycling off on just the emergency
control temp limit switch and the normal temp control switch was totally inop. The emergency back-up high temp switch was all I had to prevent a
runaway situation.
The switches are easy to check, per the maintenance manual. I would suggest a check if the heater is cycling that hot.
Steen

[Quint Van Deman]

[Zach Grant L1011jock]

Ok,
Now that I get to reread your post, I have a few questions. I see you are talking about a 180 from your other post. I also assume it is a later model 180 based on having master heat lever and separate on off selections for specific vents. Which vents are hot to the touch? Are these the vents under the panel? What about the ducts to the back seat in the sidewall, are they hot too? If this is the case, the firewall heat valve is not sealing all the way. There is always hot air flowing through the heat muff on the muffler, and the firewall valve just diverts it either back into the cowling area or into the cabin. To prove this, disconnect the scat hose from the heat muff to the firewall air valve and go fly. If you see a marked decrease in hot air flow, then you need to work on the air valve box. With the heat on, your situation is normal. All the new ducting work you probably did at overhaul has made your heater much more effective, and will probably melt rubber if someone gets their shoes too close to the outlets.

Zach

[Quint Van Deman]

[Steve Marcozzi]

Just curious from reading your old posts.... what did you ever find out about the cause of your heat problem?

Steve

[Jason Wilkinson]

Hey Steve,

I am obviously not the original poster, but I did have the exact same problem on my 1962 250. In fact my heat problem was so bad that my radio and mode c would cycle off due to heat. The problem was remedied by insuring the firewall heat box valve is completely closing. The fix is very simple (at least it was for me): (1) turn the heater to the off position, (2) remove the cowling, (3) feel underneath the heater box, there should be a large hole under the heater valve, inside that hole you should also feel an actuator flap which seals by angling in toward the fire wall, (4) all I had to do was push the flap fully in the closed position with one hand, while slightly adjusting the linkages to ensure full closure, (5) for good measure, I lubricated the linkage and checked both sides. The heater works great now and is cool in the off position.

jw

[Quint Van Deman]

Hey Steve--

The fix for me was even easier....I disconnected one of the two orange ducts where they enter the cabin. With one sucking ambient air from inside the cowling and one drawing off the muffler as designed the temperature is warm but not ridiculously hot like it was before. As we get into the heart of winter I may reconnect the second one, but for spring/fall flying it was a good keep it simple solution.

Hope that helps.

-Quint

[Daniel Haumesser]

I had the same heat concerns on my 1960 PA-24. Crazy hot air coming from the under-panel vents when turned on. Then I took note of the asbestos looking material wrapped around the heat duct manifold and deduced it was there for a reason. Just a note, if you think those short lengths of aeroduct that connect this manifold to the side ducts arent important, they are. After some work under the panel one day, I left them off because I had more work under there later and figured I'd put them back on at a later time. I suddenly had gear problems. Circuit breaker popping during retract and not resetting. Had to make my first (uneventful) emergency gear extension. Checked things out, reset the breaker on the ground and made an uneventful test flight (things had cooled off under there by then). The next longer flight, same gear problem. Another emergency gear extension two hours from home. I felt that all eyes were on me as I flew back home with the gear sticking out in a most unsexy way. Since reconnecting the aeroduct to the side vents, I have never had another gear problem. Even with the vents in the off position, it was blowing enough hot air into the circuit breaker area to effect the gear operation.

[Quint Van Deman]

Well this came back to bite me, just not in the way I expected.
When I purchased N7406P there was a warped spot in the windshield above the defrost vent. The previous owner claimed it was from a deflector that had been installed backwards but since corrected. After replacing the windshield this year I had a very deliberate conversation with my AP about the same thing occurring again. He assured me it wouldn't...sadly it did. My uber hot heat deformed a brand new (thick style) one piece windshield. I could have dealt with some melted shoe rubber, but this is going to be more expensive. So if you have flaming hot heat...beware & learn from my pain.

-Quint