Cabin Heat Cooking Avionics

[DualRatedFlyer]

Has anyone ever noticed that their cabin heater causes the avionics above the main heat outlet to cook?  

Had the heat rolling this past week on a flight down south and happened to touch the side of my 430 and it was extremely hot.  My GTX-345 is below it and I was able to reach under the panel and touch its metal baseplate and it was also extremely hot. 

On the return trip I opened my left eye fresh air inlet (beside pilots left knee) and pointed it up towards the avionics which appeared to help a little.  The biggest difference was when I turned off the cabin heater.  With the heat off the avionics are no longer scalding. 

When its on, I can feel warm air coming out above the top of the center floor vent where the throttle quadrant is.  I believe its venting behind the plastic finish around the center floor vent up into the avionics deck.  

 

Has anyone experienced this before?  Not sure what it looks like behind the plastic center console trim.  Looks like I may be taking it off to figure out how to better seal it up. 

[steingar]

Now that you mention it, my radio started loosing frequencies very recently.  I bet it started when I started using cabin heat, since that only began recently.

[neilpilot]

Do you have an avionic cooling fan.  If you do, check to see if the fan's inlet can be relocated to lower inlet air temp.

[DualRatedFlyer]

Not sure- Its a fairly new aircraft to me, and I saw no mention of one in the maintenance records.  For reference, its a 1974 M20F.  

Would the cooling fan be visible under the dash?

 

Edited November 27, 2017 by DualRatedFlyer

[Marauder]

Not sure- Its a fairly new aircraft to me, and I saw no mention of one in the maintenance records.  For reference, its a 1974 M20F.  
Would the cooling fan be visible under the dash?
 

More likely what is happening is one of the SCAT tubes is off and blowing on your avionics. The tubes may be black or orange. The one I would look for is the one that goes to the defroster panel for the windshield. It is a bear to get on and it may have fallen off.


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[Marauder]

I have a 75 F.


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[DualRatedFlyer]

@Marauder - here is a photo I snapped while working on another project a few weeks ago.  The view is below the panel on the co-pilot side looking up.  Would the orange tube on the right be the scat tube going to the defroster? 

 

It feels like the air is coming out somewhere above the cream colored "Alt Static" knob on the bottom left.  Not sure if the plastic trim behind the alt air knob is directing all the heat directly up.  The metal trays were so hot I couldn't keep my hand on them for more than 5-6 seconds.  I cringe to think what the heat is doing to my avionics insides. 

 

[cloud116]

I have a 75 F and had the same concern. I Noticed the housing along my right leg would get extremely hot when I pulled out the heat knob. Then I started mixing cabin air with the blast furnace that results from pulling out only the heat knob. The center console cooled down nicely and I still get plenty of heat in the cabin.  

Given the other posts, I’m gonna see if the defrost hose is disconnected. In any event, the above solved my problem. 

[Marauder]

2 hours ago, DualRatedFlyer said:

@Marauder - here is a photo I snapped while working on another project a few weeks ago.  The view is below the panel on the co-pilot side looking up.  Would the orange tube on the right be the scat tube going to the defroster? 

 

It feels like the air is coming out somewhere above the cream colored "Alt Static" knob on the bottom left.  Not sure if the plastic trim behind the alt air knob is directing all the heat directly up.  The metal trays were so hot I couldn't keep my hand on them for more than 5-6 seconds.  I cringe to think what the heat is doing to my avionics insides. 

 

I am looking at the thread on an iPhone and don’t see the picture you posted. The tube I am thinking about is the one that goes up to the glareshield in front of the pilot side. It is about an inch in diameter. 

Here is a picture of the tube  

 

Here is where it attaches  

[DualRatedFlyer]

@Marauder not sure why it didn't work.  I've added it as an attachment this time.  I think we're talking about the same tube.

 

@cloud116 My wife has been complaining of cold temps in the back seat and I found that by mixing the heat and vent it eliminated the negative pressure draft coming in from the rear seat vents and more evenly distributed the heat (advice I found in another forum on this site).  In addition to mixing I pointed the pilot vent on the avionics, so not sure what effect mixing has alone.  Sounds like you've had good luck.  

Even after the mixing the 430 and 345 feel hotter than I think they should.

[N201MKTurbo]

You might consider putting some fiberglass insulation between the air box and the radios.

[Yetti]

There should also be a radio cooling tube. Clear plastic 1 ".  Coming from copilot side vent. Top of vent. Check for obstructions

[kpaul]

FWIW most of those boxes get very hot even with cooling.  In my work planes - PC-12s, the 430W get blazing hot as does many of the other components we have installed.  Also we regularly operate in locations where the ground air temp is 55°C (130°F) and I have yet to have one shut down or have reduced functions due to heat.  The GTN 650 in my Mooney gets hot, but I have not noticed increased heat with the heater pulled, although I never run full hot with no fresh air mixed in, I do not currently live in an area that requires that much heat.

 

[Hank]

15 minutes ago, kpaul said:

although I never run full hot with no fresh air mixed in, I do not currently live in an area that requires that much heat.

 

Even when I lived along the Ohio River, I never ran full Heat with no Cabin Air mixed in. Usually they were both pulled most of the way at startup, reduce heat NLT initial climb, then after leveling off, remove coat and push heat in until ~1/3 out with Cabin Air at least half out.

[DualRatedFlyer]

12 hours ago, N201MKTurbo said:

You might consider putting some fiberglass insulation between the air box and the radios.

This a good idea.  Going to give it a try

[DualRatedFlyer]

1 hour ago, Yetti said:

There should also be a radio cooling tube. Clear plastic 1 ".  Coming from copilot side vent. Top of vent. Check for obstructions

Will give this a look this weekend.  Thanks for the suggestion. 

[DualRatedFlyer]

21 minutes ago, Hank said:

Even when I lived along the Ohio River, I never ran full Heat with no Cabin Air mixed in. Usually they were both pulled most of the way at startup, reduce heat NLT initial climb, then after leveling off, remove coat and push heat in until ~1/3 out with Cabin Air at least half out.

@Hank I was primary running full heat to try and get the rear seats warm.  Looks like mixing does help move more air more evenly, but even then my avionics still get hotter than id like.  I have heard rumor of scat tubing that runs to the rear seats to deliver heat, but I dont know where the heat exits in the rear and have been unable to find the vents.  

[DualRatedFlyer]

51 minutes ago, kpaul said:

FWIW most of those boxes get very hot even with cooling.  In my work planes - PC-12s, the 430W get blazing hot as does many of the other components we have installed.  Also we regularly operate in locations where the ground air temp is 55°C (130°F) and I have yet to have one shut down or have reduced functions due to heat.  The GTN 650 in my Mooney gets hot, but I have not noticed increased heat with the heater pulled, although I never run full hot with no fresh air mixed in, I do not currently live in an area that requires that much heat.

 

Thanks for sharing.  Looking at the manuals ambient temp ranges for the 430: -20°C to +55°C and -40° C to +70° C for the GTX-345.  I dont think the heater is putting out that kind of heat when blended. 

Still dont get warm and fuzzies knowing the unit is scalding hot - these things cost too much to break. 

A few good suggestions on here will hopefully help mitigate these temps. 

[kpaul]

5 minutes ago, DualRatedFlyer said:

I have heard rumor of scat tubing that runs to the rear seats to deliver heat, but I dont know where the heat exits in the rear and have been unable to find the vents. 

In our Fs you are only getting the heat from the center vent below the T-P-M controls.  I have considered using a tube from the center vent to the back, as it seems that only my daughter gets cold back there.  Once I move to cooler climates I will think about it more.

Here in Florida I occasionally run the heat a little at altitude.  I also occasionally run it just to watch my CO2 detector and check for any leaks/changes.  So far my Sensorcon has not shown an increase in CO2 with the heater on.  

[kpaul]

1 minute ago, DualRatedFlyer said:

Thanks for sharing.  Looking at the manuals ambient temp ranges for the 430: -20°C to +55°C and -40° C to +70° C for the GTX-345.  I dont think the heater is putting out that kind of heat when blended. 

Still dont get warm and fuzzies knowing the unit is scalding hot - these things cost too much to break. 

A few good suggestions on here will hopefully help mitigate these temps. 

I have been surprised as to what the boxes feel like to the touch.  Yes we often test the outer limits of our planes overseas. Nothing like looking at the cockpit temperature and see 65°C prior to engine start.  Not going to miss ground operations on days like that.

[DualRatedFlyer]

6 minutes ago, kpaul said:

In our Fs you are only getting the heat from the center vent below the T-P-M controls.  I have considered using a tube from the center vent to the back, as it seems that only my daughter gets cold back there.  Once I move to cooler climates I will think about it more.

Here in Florida I occasionally run the heat a little at altitude.  I also occasionally run it just to watch my CO2 detector and check for any leaks/changes.  So far my Sensorcon has not shown an increase in CO2 with the heater on.  

Are you saying that there is no scat tubing going to the rear in the F model, or that the flow through this tubing is so negligible that your really only getting heat from the TPM vent?

If I could just get that vent to extend a little further out (anyone have a easy diy mod?).  My wife is always cold, and im always hot.  Wonderful combination when trying to pump heat into the rear. 

[Oldguy]

20 minutes ago, kpaul said:

In our Fs you are only getting the heat from the center vent below the T-P-M controls.  I have considered using a tube from the center vent to the back, as it seems that only my daughter gets cold back there.  Once I move to cooler climates I will think about it more.

Here in Florida I occasionally run the heat a little at altitude.  I also occasionally run it just to watch my CO2 detector and check for any leaks/changes.  So far my Sensorcon has not shown an increase in CO2 with the heater on.  

It is the same in my J. And changing tanks after the heater has been on can be painful if you are not careful and fast. The first time I swapped tanks after running the heater, the lever almost left a blister  on my fingers.

[kpaul]

22 minutes ago, DualRatedFlyer said:

Are you saying that there is no scat tubing going to the rear in the F model, or that the flow through this tubing is so negligible that your really only getting heat from the TPM vent?

Correct there is no tubing going to the rear, just the exhaust vents next to the rear seats that help "pull" the air aft.

22 minutes ago, DualRatedFlyer said:

If I could just get that vent to extend a little further out (anyone have a easy diy mod?).  My wife is always cold, and im always hot.  Wonderful combination when trying to pump heat into the rear

Do you still have the original square flap vent in the front, like the one pictured below?

 

I have since "upgraded" to this which would allow a tube to be attached easier.

 

[DualRatedFlyer]

@kpaul  Wow, I wasn't aware the F didn't have rear vents.  Looks like I can stop looking for them now.  Do you know what model they stopped with?

 

I still have the square vent similar to your picture above. Mine looks more like 3 or 4 fins that close flat instead of a butterfly valve.  I like the "eye vent" idea.  Might have to give that a try. 

[TTaylor]

The F is very cold in the back seats.  I have a box/tube I place between the front seats in winter to help direct the warm air to the rear seats.  We often fly when it is below zero outside.  I am replacing the lower heat vent on our F and have thought of designing a way to attach a scat tube for winter flights.