GNX 375 heating issue?

[oldguyscanfly]

Recently I was flying from Payson AZ to  Liberal KS. Was at 13,500, and running my cabin heater full on. ATC informed me my altitude reporting was showing me bouncing between 8,000 and 30,000'. I had no indications or messages from the unit of a malfunction. after numerous tries at resetting, no joy, and ATC had me disable altitude reporting. 

I kept trying to diagnose the problem, and began to receive error messages of a altitude reporting fault, and the loss of ADSB. 

I noticed it was fairly warm around the unit, so turned off the cabin heater. Sure enough, in about 15 minutes everything came back, and continued to operate normally the rest of the trip. It felt warm, but I didn't think excessively so. Going to take my IR gun on the next flight to get some good readings.

I also want to take a look at the scat hoses under the panel, make sure nothing has come loose or is somehow directing hot air towards the stack. 

Any other ideas?

Has anyone else had a similar issue?

[carusoam]

OG,

What do you have for...

• Altimeter
• Transponder
• Altitude encoder

Sounds like the heater is somehow disabling the flow of information to your transponder...

Could be as simple as a loose wire...

PP thoughts only, not a mechanic...

Best regards,

-a-

[oldguyscanfly]

The transponder is the GNX 375. It's the all in one Transponder/ADSB/Nav unit. I assume it draws its altitude info from my

G5 PFD, and not the old steam gauge altimeter. I'm going to the hanger tomorrow to do some under the panel gymnastics, see if I see anything.

[tmo]

How are you getting the altitude to the transponder? If via Gray code one of the multiple wires might be loose or have a bad crimp / solder.

[oldguyscanfly]

 

I assume its binary from the G5 unit, but unsure. Have a call out to my Avionics guy. 

[Ragsf15e]

I gotta think one of your heater scat tubes is disconnected or has a hole. I want the heat on me, the electronics can make their own!

Maybe check the defroster tubes?

[carusoam]

The manual for the GNX375...

Has an interesting trouble shooting guide...

If you had a message...

It does have temperature sensing capability...

And seems to be sensitive to temperature...

Section 6-2, near the end...

https://static.garmin.com/pumac/190-02488-01_b.pdf

 

I was looking for some info related to the static port connection when I came across the manual...

Didn’t find anything regarding the plumbing... that may be the install manual...

Pp thoughts only, not a mechanic...

Best regards,

-a-