I know it’s a long shot since this isn’t specifically an HVAC forum (I already posted this message on hvac-talk.com and didn’t get much feedback), but I figured I’d try and see if anybody has ever seen anything like this.  Thanks in advance for any replies.

Background: 2-ton Trane XV18 heat pump + TAM9 air handler. Installed January 2019.  Thermostat is an XL1050 that was replaced with a new 1050 in June 2021 (the original stat had a flickering screen and eventually stopped working). Evaporator coil was replaced under warranty in September 2021 due to a leak. Thermostat is connected to wifi so theoretically should be running the latest firmware. System has a Comfortlink II zoning system. System has been working perfectly fine in both heating and cooling modes all winter and so far this spring.

 

Issue: A technician (who I believe to be very knowledgeable) was at my house earlier this week for spring preventative maintenance. Outdoor temperature was about 70. Indoor temperature was about 73. The technician reported that the compressor would not turn on when he put the system into “charging mode-cooling,” which is a particular diagnostic mode used to charge the system or check the charge.  Everything else (indoor fan, outdoor fan, etc.) would turn on in “charging mode-cooling” except the compressor. The tech spent an hour on the phone with Trane tech support, tested various parts of the compressor for shorts, tested the wiring harness, and who knows what else, but could never get the compressor to turn on during “charging mode-cooling.”  Compressor works fine under normal operation and even under different diagnostic modes except for “charging mode-cooling.”

 

Anybody ever seen anything like it?  Where the compressor refuses to turn on in a particular diagnostic mode?  The technician and Trane tech support ended up concluding it was probably either a faulty thermostat or just a software glitch that might be fixed in the next update. Recommended waiting until fall preventative maintenance to see if its still doing the same thing.