It is an in-line duct fan.
Thanks for all the replies. I appreciate it. I would buy a new fan if I could. I will eventually. I am also way too afraid of messing my light up to take it apart.
I am going to hook the 4" up to the duct work for the veg room and the 6" up to the duct work for the flowering room. Does anyone know if this will work, since the duct work for both rooms meets and goes into one line of duct? Maybe this will help. I am also going to get a computer fan to help pull in more cooler air. I just need a solution for a month or so until I can afford a bigger fan.

P.S. - what signs should I look for concerning damage to my plants from the heat? I haven't noticed any yet, but it has only been in the 90's for one day of 18 hours. They still look as healthy as ever.