I am currently dealing with the 2nd occurence of a UNIT OVERTEMP error on my IFD-540. 

My saga begins with a massive avionics upgrade project for my aircraft.  My new avionics stack from top to bottom is:

The 1st occurrence happened after 6 flights and 4.5 hours of flight time from installation of my new to me, factory refurbished unit.  The 1st error was UNIT OVERTEMP (36).  The fix for this permanent error is a trip back to Avidyne and a thorough inspection for any damaged or failed components; only with that clean bill of health, then the error flag is reset and the unit returned to the customer (me).

After the repaired/returned IFD-540 was reinstalled in my aircraft and and installation configuration settings made and returned to service by the shop, I picked up the aircraft and made a successful 11 minute flight to my home airport.  No issues.

I went to my airport with the plan to upgrade databases and check and/or restore some personal setups on my IFD-540.  All of this was done with ground power and the engine not running on a 76 F degree day, while in the hangar.  After 20 minutes of my electric Master On, Avionics Master On, and PMA450a, Lynx NGT-9000+, and IFD-540 ON; my IFD-540 displays a red UNIT OVERTEMP (6) error again.  I have a support ticket opened with Avidyne technical support currently and am being instructed that the IFD will again have to be returned to Avidyne.

Has anyone else had this issue?  Is this a unit or installation issue causing my problem?

I just want to fly and have my airplane whole and healthy.

Gring wrote: Did you check to see that both the internal fans are running at the appropriate speed (~10k rpm)

Yes,  see my photo of the fan speeds and internal temps.

Also, pics of the internal temperatures.

I just got off of the telephone with Avidyne Technical Support.  After reviewing the units 1st trip back to them and repair actions taken, plus seeing the error, fan speeds, and internal temps, they are thinking that a temperature sensor itself may be bad, and falsely causing the error.  They have seen a temperature sensor fail like this, but it is infrequent.  This still requires a 2nd trip back to Avidyne to correct the issue and reset the error.

We fly in Arizona.  Intense sun, ground ops with air temperatures in excess of 100 deg F (but cruise at altitude to keep the air temps below 80).  Have never had any overheat problems with our IFD 540.   We do not have a cooling fan, although a small (7/8" SCAT) duct brings outside air to the back of the stack.

I'll have to look at the temps the next time I'm doing a warm flight.

What was the ambient temp?

Also, what kind of aircraft, and are the side edge vents unobstructed?

Overheat has not been much reported here, that I recall, and there are a lot flown in areas far hotter than Switzerland.

* Orest

Overheating is an issue that has occurred to a number of IFD owners and in my case to both boxes on the same flight at 16000ft. Cabin temperature was comfortable, so it must have been installation related which means they aren‘t as tolerant and flush mounting requires extra ventilation from the back.

* Orest

I did fly it to the Bahamas in March with no issues, and just got back from a flight to Salmon ID. On the return trip to MN we landed in Gillette WY, it was HOT, Ipad overheated but no issues with the IFD.

Anything I should do proactively?

There are other TB owners here that have not experienced my problem. Might be dependent on where in the stack the boxes have been mounted and what other boxes are below or above them. It is clear that flush mounting deteriorates the heat dissipation through the side vents of the bezel.

Well, it looks like you are not having a problem. You could just keep an eye on the annunicated temp, directly or by checking the logs - -  but you are not even getting a warning. 

* Orest 

If you want to proactively do something check whether your ram air duct is correctly attached to the left hand naca vent and the plastic stub at the back of the avionics stack.