Cabin heater seems to always be engaged

[UteM20F]

Our F model is warmer than comfortable after 20 minutes of flying, even on a cold (35F degree) day, without engaging the cabin heat.  We had an A&P check it out and he said the cabin heat 'door' seemed to be working properly.  We bought the plane last January, but didn't fly it April - September as it was in the shop getting all new avionics.  We'd like an answer before the hot weather comes.  Any ideas if this is normal, or if not, what a solution might be?  

Thanks,

Ute

[carusoam]

Ute,

not normal…

next…. Put thermocouple in the heat outlets in the cabin…

If heat is coming in… it will show up there first.

 

Depending on the year of your plane… the heat system has slide gates or butterfly valves…  newer Mooneys got the butterfly valve…

Either way you can look to see for yourself if they are closing all the way…

Slide gates have a tendency to stick about nine months after being lubricated during the annual…

 

if you have the butterfly valve… there is a good chance that the silicone rubber seal inside is no longer sealing… allowing hot air to by-pass into the cabin…

expect to be cutting a piece of silicone rubber for a perfect fix… 

or cleaning and lubricating the slide gate for a perfect fix…

Speaking of heating system….   Always good to have a good CO monitor as well….

PP thoughts only, not a mechanic…

Best regards,

-a-

[Ragsf15e]

9 minutes ago, UteM20F said:

Our F model is warmer than comfortable after 20 minutes of flying, even on a cold (35F degree) day, without engaging the cabin heat.  We had an A&P check it out and he said the cabin heat 'door' seemed to be working properly.  We bought the plane last January, but didn't fly it April - September as it was in the shop getting all new avionics.  We'd like an answer before the hot weather comes.  Any ideas if this is normal, or if not, what a solution might be?  

Thanks,

Ute

Pretty easy to open the mixing box and have a look.  Let’s just say the control cable and butterfly valve that mix warm air with cold isn’t exactly a swiss watch. My ‘68 F has that box under the cowl on the copilot side, high up near the top and aft near the firewall.  Likely your heat isn’t shutting off enough.

[Guest]

1 hour ago, UteM20F said:

Our F model is warmer than comfortable after 20 minutes of flying, even on a cold (35F degree) day, without engaging the cabin heat.  We had an A&P check it out and he said the cabin heat 'door' seemed to be working properly.  We bought the plane last January, but didn't fly it April - September as it was in the shop getting all new avionics.  We'd like an answer before the hot weather comes.  Any ideas if this is normal, or if not, what a solution might be?  

Thanks,

Ute

The flapper door should have a seal which closes tightly against the short tube in the firewall shut off valve.

[jetdriven]

F models had the slide gate feature like the early 201s which basically didnt seal off. They leaked hot air. The 1979 and later style with a flapper valve work great when you add a thin sheet of silicone rubber On the flapper to seal against the tube.  

[DCarlton]

2 minutes ago, jetdriven said:

F models had the slide gate feature like the early 201s which basically didnt seal off. They leaked hot air. The 1979 and later style with a flapper valve work great when you add a thin sheet of silicone rubber On the flapper to seal against the tube.  

Yeah mine has the slide gate.  I removed it last year, buffed off the corrosion, primed and reinstalled.  Seems like I remember having to adjust the angle of the cable too.  It works a bit better.  

[Guest]

That contradicts with the IPC for F models, never trust what’s written

[Ragsf15e]

2 hours ago, jetdriven said:

F models had the slide gate feature like the early 201s which basically didnt seal off. They leaked hot air. The 1979 and later style with a flapper valve work great when you add a thin sheet of silicone rubber On the flapper to seal against the tube.  

I think there’s a Year cutoff, not a model.  My ‘68F has the butterfly valve that is on @M20Doc’s diagram, not the slide valve.

I do think the ‘67s had the slide though.

[UteM20F]

Mine is the '67.  Thanks all of you for the great info, especially the pics.  This community is awesome!

I'll look at it next time I'm there and see if I can understand what you are telling me, specifically how the silicon piece will work.  I'm definitely not good with mechanical things and seldom would trust the work that I am able to do, but I do want to be able to explain the issue to our mechanic properly.

And I also agree that we need to invest in a CO monitor, especially with the flaky heating system.  

Thanks again,

Ute

[carusoam]

Ute,

Find @DanM20C…. I think he posted the latest discount code for one of the best CO monitors around…

Many Mooneys are carrying a Sensorcon or two…

My 65C had a pair of slide gates for cold and hot air… on the engine side of the FW…. Not too hard to get too…

Much easier with the help of your mechanic…

+1 for all the great MSers sharing their great knowledge….

One day… you will be one too.  

Best regards,

-a-

[AIREMATT]

If you do have the butterfly, check the pivot hinge bar. It is a different metal that disintegrated in mine and prevented the butterfly from even reaching the shutoff port to close the heat off. If you don’t get it fixed before the warm weather, it will be very uncomfortable in flight…

[Utah20Gflyer]

I had this issue on my 1968 G model which has the flapper.  The silicone washer had come off so it was just metal on metal which didn't seal very well.  I found the silicone washer in the duct.  After cleaning everything up and getting the silicone washer back in place the problem was solved.  

[cliffy]

You might want to read the Inflight Engine Fire Check List

First item is shut off the Cabin heat  

If you can stop the heat you may have a real problem in an emergency. 

It needs to be fixed

[AIREMATT]

4 hours ago, cliffy said:

 

If you CAN’T stop the heat you may have a real problem in an emergency. 

It needs to be fixed

I think you meant can’t…

[UteM20F]

If you CAN’T stop the heat you may have a real problem in an emergency. 

It needs to be fixed

Thanks guys.  I completely agree with your thinking.  We're buying the CO monitor and our A&P is coming, hopefully this weekend.  I hope I can report that it is completely resolved very soon.  

Ute

[Pinecone]

Also, cabin heat is a major place where CO comes into the cabin with an exhaust leak.

You REALLY want to be able to turn it off.