Hi everyone . Have cascadia 2015 with1.5m kms . Air conditioner stoped working and it was running really good . Reached in yard checked codes and found SPN876 FMI1 ( but there were no engine lights on dash).
Asked mechanic and he said looks like AC compressor . I decided to drive it for another day . So today LOW VOLTAGE sign came up on dash . Alternator was charging only 11.8 .
Had extra alternator in bunk , so changed it In rest area . After 45 minutes I was back on the road . And found air conditioner started working. Guessing ac compressor wasn’t getting enough voltage from faulty alternator .
Thought it could be helpful for someone else in future .