On Mon, 14 Jul 2008 21:14:22 -0500, Don Young wrote:

If the motor is reversable, the fins straight, can I change the wiring
to be only an exhaust fan, i.e., not add any additional wiring? I
might never need this to function as an evaporative cooler again.
It depends if you're willing to get on the roof to flip a switch.

Squirrel cage blowers are mainly centrifugal and will not effectively
reverse the airflow when the motor is reversed, regardless of the fin
configuration. They use leading, straight, or trailing fins but they all
blow in the same direction, from the center to the outside.

duh, uh, you're absolutely right. It won't matter what direction the
fan turns; centripetal force will cause the air to flow to the outlet
as always.

Forget it. Just get a whole house fan and install it somewhere else.