Okay, I'm not genius on any of this but I noticed something weird in your diagram and thought I would bring it up. On relays 1 and 2 you have the power (+) going to the 87 terminal and return (-) going to the 86 terminal. It's different on relay 3, i.e. reversed. I'm not sure if this amounts to a hill of beans but thought I would mention it. It seems like the left fan is not getting power (from your explanation) and running the power through your diagram is where I saw the above explanation.