As Matt pointed out, the TRH.12m.c fan died yesterday.  To avoid further possible damage to the fan, I've logged in and set the fan duty cycle to 0, which hopefully will effectively turn the fan off.  If we get a warm day, I'll try to turn it back to 40% to see if the fan restart.

BTW, the process to change the duty cycle is:

ssh cu

rs 4

control-U (enter TRH settings menu)

DUT 40

EXT (exit TRH settings menu)

control-c (exit rserial)

exit (exit ssh session)