Well, I would not drive without aux fan. It works always with AC but also suppose to start with a very engine temp. I really would install one. By the way, check if the fuse box has a fuse for the auxillary fan. If it does not, you probably do not need it.
1985 190D 2.2l Sold-to Brother-in-law
1996 Mustang 3.8l -"thinks it's a sports car"
1988 Grand Wagoneer - Sold (good home)
1995 Grand Cherokee Ltd -"What was I thinking??!!"