I have MBP 2017 (MPXT2) bought about 3 months ago.
I noticed that when it heats enough, only right fan starts blowing away hot air. On the other hand the left side is not that hot and it is probably ok that I have never seen left fan working. I wonder is it expected behaviour for new MPB 2017 or the left fan is probably broken? I do not even know what can heat the left side because the GPU is built-in.
Update: Used Macs Fan control as suggested. It shows only one fan.