The units are approx. 4 years old and I've given up on the installer to troubleshoot and repair issues. I am relatively handy and thought I'd give it a try myself. I have two AUC1D120A9601A units twinned together. They operate as 1 unit and utilize a single-blower to supply forced air to my home. I will refer to them as F1 and F2. I attempted to start up the unit last weekend, and found that only F1 was running. F2 had a 3-flash LED error code. I followed the troubleshooting tree in the Installers guide, and all checked out okay. I decided to start swapping some parts (with spares and or between F1 and F2 to confirm what I suspected was an IFC failure). I changed the pressure switch and the inducer - no change in performance. When I swapped the IFC boards, the LED fault moved from F2 to F1, and now only F2 would run. I ordered and installed a new IFC (CNT2891) for F1. When I removed the IFC board from the bracket for F1, I found a burn mark on the bracket and back of the board. It is located above the HUM-H stake-on (where it looks like there could be a stake-on but there is not). I felt pretty confident I found the problem. Upon starting up the unit, F1 (with the new IFC board) ran as expected... but once again I had the 3-flash LED fault code on F2. I didn't have the heart to pull the board on F2 and see if it has a burn mark, but my guess is there's some type of short in my wiring and it is shorting the board on F2. Not sure I can explain how the fault moved from F2 to F1 when I swapped the boards though. Can you suggest where I might look to solve the problem? I'm already in for $150 for the IFC, and I'm going to guess I need another one as well. Thanks in advance for any/all advice...

i have an american standard furnace when i call for heat the blower is the first thing to come on and it wont shut off also the circuit board light does not blink it just stays solid red please help