I had one of these 6 1/2" fans on my 64 GMC 960. On full it really moved the air around the cab, winter and summer. It has a small rheostat to adjust the speed. If you have a contact for school buses these are virtually a standard option. The company who supplied GM still exists and there prices are out of this world. They wanted close to a hundred dollars for a replacement switch.
The description of the fan states that it's a quiet operation, not when it is on full!
