GTN 750 not talking to KAP 225

[wcooper31]

I just upgraded from GNS 530 + 430 to a GTN 750.  I have a KAP 225 auto pilot.  When plotting a Direct To course with the GPS and then pressing the NAV button on the auto pilot, nothing happens.  I can get the NAV button to work when I use the VLOC to see a VOR or ILS freq, but not in GPS mode.  If I want to fly a GPS route, then I use the Heading Bug and select HDG on the auto pilot and self-correct for wind/drift.  Sarasota Avionics is where the work was done and they are talking with Garmin to troubleshoot. 

Has anyone come across this situation before?

Edited February 28, 2016 by wcooper31

[Godfather]

This sounds like an install or setup issue.  However, I have zero experience installing or wiring up these units.  I'd imagine you have a BK 525 HSI and I'm not sure if the gpss wire runs through that unit or has a direct connection with the AP.  Never had a similar problem with updates in the mooney over the past 15 years (530/430->530w/430w->750/650).  If you said the problem was on approach there is a sequence to enable the approach that IIRC changed from the non waas units to the waas units.

[wcooper31]

Thanks for the reply.  On a ILS approach, everything works fine.  The problem is once I select the CDI to GPS on the GTN 750, then I can no longer use the auto pilot in NAV mode (I must select HDG on the auto pilot and spin the bug on the HSI to follow the magenta line on the GTN 750.  I agree, this must be an install issue, but wondered if someone knows if it is a simple setting that was overlooked or is it something more major than that.  

[Jerry 5TJ]

The GTN750 requires key press activation of autopilot outputs each time before pressing APR on the King 225. (Described in Garmin 750 manual) Does that sequence work on your installation ?   Also if you have G500 and GDL43e the GPSS mode is selected via the G500 HDG button and the King 225 is used in HDG, not NAV mode.   

[wcooper31]

Solution found:  It was a GAMA setting that was not correctly selected when the GTN 750 was installed.  It took 30 seconds to make the fix by going into the 750 and then the GPS worked with the KFC 225.

[carusoam]

Nice Pirep, WC!

It is always good to have the positive results explained.

Best regards,

-a-