All of these recurring and unexplained faults were found to be inverter software issues. However, the compressor drop out fault could also be a loose high pressure molex plug connection in the control panel.

  These are all faults that will occur with 5 speed units that have version 5 or earlier aoc software and pre-version 3 moc software. These are units manufactured in 2014 and 2015.

 The  5 speed units have an application operating control board (aoc) and a motor operating control board (moc). The aoc board mounts to the bottom of the moc board. The entire assembly is called the inverter kit.

   The release of the version 7 aoc software corrected these issues. The solution was to replace the aoc board with the updated version 7 board. However, this led to another problem that soon surfaced and usually on the hottest days, during peak load conditions.

This problem is only with the units that have the 3 ton inverter: 24a, 25, and 36 model units- 2014, 2015 up to 17th week of 2016.

Code 71 compressor drop out

   This code does not appear in the fault history of the user interface.

It is a local fault that flashes on the aoc board status code led. Removing and restoring power to the condenser or heat pump will clear the fault and get it temporarily up and running.

Version 7 software corrected all of the faults first mentioned, but did not communicate properly with versions 1 and 2 moc boards. (The moc board is the actual inverter, by the way.)

It created a “race condition” (Carrier’s terminology for racing the compressor rpm’s) where it would cause very high head pressures, in excess of 400psig. The miscommunication between the two boards, would cause the moc to report 0 rpms to the aoc. The aoc would in turn make the moc ramp up the compressor rpms, causing these high head pressures. It would eventually either just lock out thinking that the compressor had dropped out, when actually it hadn’t or the compressor would actually overheat and drop out. Carrier has never definitively explained that particular part and which was actually occurring. But, I’ve yet to see a code 71 drop out with open windings, with the exception of units found to be overcharged.

 Enter version 9 aoc software and version 3 moc software. No, they didn’t skip 8. Version 9 includes the unreleased version 8 update.

This fixes the code 71 issue and a few other things.

Replace the entire inverter kit in order to correct this issue. Although I said this is only an issue with the 3 ton inverter on 3 and 2 ton units, the version 9 update does change some things with the other tonnages.

Bottom line:

If you encounter a Carrier or ICP 5 speed unit with any of these faults, or have installed one;

pull up the outdoor unit model number in the user interface.

Lastly, all of the aforementioned faults can each be actual issues that aren’t software related.  However, it is virtually always software related, with the exception being a gross system  overcharge. Overcharge also being the most common problem with these systems aside from software issues.

I hope this helps somebody.