Defroster is there such a think

[FlyboyKC]

I have a 1968 M20G and was noticing behind the glareshield there are all these holes which look like they are for airflow for a defroster type function for the windshield. However, I don't have any separate controls and when I have the cabin heat on it doesn't seem like is any airflow going to the windshield. I was just curious if there was supposed to be and things to look at maybe I am missing.

Thanks for any comments.

Neal
 

Edited February 20, 2016 by FlyboyKC

[takair]

You need to close off the other vents to force the hot air into the defogger.  Barely works on the ground when you would really need it.  Have been thinking of adding a blower to cover this.  

[Hank]

Look under the panel on both sides, there should be a tube ~1-1/2" that blows hot air into both foot wells. There's a knob to turn that will close these; when closed,cabin heat blows through the defrost vents. Nothing much comes out unless you pull the cabin heat knob. Sorry I don't have a picture.

[FlyboyKC]

Thanks, I will take a look. I think on my last flight I did close the floor vents and had the cabin heat on, but I will have another look just in case I missed one.

[carusoam]

There are many parts of that system that get old over time.  Hoses, air valves, controls, and that kind of thing...

It is pretty easy to find and update, or lubricate.  Don't be surprised to find an old hose has come off or kinked so air no longer flows through it.

More modern Mooneys include a fan in the system to improve the airflow to the window.

Best regards,

-a-

[TWinter]

If you look in the POH there is a section that gives the exact combination of where the vents etc need to be positioned either opened or closed to get the defrost benefits. Doesn't work great, but they do have a combination that is supposed to be the defrost combination. There also a brief warning in there about directing too much heat on the windshield.

 

 

-Tom

[N201MKTurbo]

I have found that even in the worst icing conditions, the defroster will clear a half inch high strip of your windshield....

[Mooneymite]

7 minutes ago, N201MKTurbo said:

I have found that even in the worst icing conditions, the defroster will clear a half inch high strip of your windshield....

Given enough time....

[Shadrach]

I renewed all of the ducting behind my panel at last annual. I detailed the routing and ensured all passages were in the open position. The difference has been night and day.

[Shrobby]

I also finished a annual and Don Maxwell found the two vents were also coming apart. Each vent has like 5 holes to disperse air. They are held in by four rivets. I would have those checked.

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[Shrobby]

Here is where they are.

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[FlyboyKC]

Well I solved my defroster issue. I replaced a scat house going to one side and that didn't work. So I unplugged it from the junction box and hooked up my shopvac blower and air moved out of the defroster. So I little stumped I decided to poke my finger in the hole (lets keep this at a rated G level) and felt something rubbery like a flapper valve. So I took off the larger scat hose and found the pictured rubber disc just kind of laying against the opening and blocking my defroster hoses. I have no idea what this goes to. My defrosters work good now, and the planes cabin heat seems to be a little more equally distributed. 

 

Any thoughts on the rubber disc?

[N201MKTurbo]

That is item 12 in the IPC. It is a rubber seal that goes in the air Box in the engine compartment. It must have come loose and been blown into the inside air box.

 

 

 

Edited March 6, 2016 by N201MKTurbo

[Mooneymite]

Wow!

Ain't Mooneyspace great? I'd have NEVER known that.  

 

[carusoam]

That appears to go between two steel discs, providing a seal.  See if you have all the parts to put it back.  This way the airflow will get closed off during the warm months...

The 65C used slide gates in that location.  They would get rusty and become a little challenging to slide....

Best regards,

-a-

[KyleKJ90]

I know this may seem a little off-kilter, but I found what I believe to be the best method to keep foggy windows at bay during taxi (at least in my case) was to open the overhead air scoop and turn pull the cabin heat knob fully out/HOT. Despite the below freezing temperatures, the fresh air coming from the overhead vents didn't seem that cold and combined with the lukewarm air coming from the lower vents, the windows seemed to clear up slowly but surely. It definitely keeps my windows clean until I'm ready for departure if I open them before closing the door and starting up. Definitely would close those bad boys on the takeoff roll though! Try it out sometime and see what you think.