AP doesn't follow the heading bug

[MooneyBob]

My Century IIB doesn't turn to the heading bug setting. In the HDG position it just turns right. It looks like it works fine in NAV and OMNI modes. Where should I start to look? 

[jetdriven]

A loose pin or wire in a connector between the DG and the radio coupler, or between the radio coupler and the console. You need he horizon to be level for this test. Usually we have a drill mounted vacuum pump we hook up to the vac hose under the cowl.  Turn the autopilot on and move the heading bug left 90 degrees to the current heading. The yoke turns right as you say. Then give all the connectors a good wiggle and shake.  When you find the right one, it starts to turn left.  The connectors are blue, circular and about 1/2" in diameter, with pot metal shrouds on them that lock them together. 

The Cehtury is a good autopilot. The split pin connectors are the downfall. I just hooked up GPSS to mine and it flies RTF GPS approaches and holding patterns, etc like the 737. 

Edited July 2, 2017 by jetdriven

[N201MKTurbo]

Look at the connectors on the DG and radio coupler. I would start by just reseating them. You can test it on the ground by moving the heading bug left and right of the center. The yoke should move in the other direction to correct to the bug. 

[sgrooves]

I had that issue with my aspen/stec55x combo. Just a slow turn to the right regardless. Turns out the ACU was bad. Luckily it was replaced under warranty, labor still was $$.

[AH-1 Cobra Pilot]

I had similar problems with my Century III AP, except it was in the NAV mode; the heading bug worked fine.  Eventually, everything went, except the Altitude Hold and Pitch.

My Avionics Guy replaced/fixed the pins, now all is well.