I have a furnace in my basement where it is cool. My upstairs gets really hot in the summer. I heard a DIY guru on the radio say that some furnaces offer a "fan-only" option so that the furnace can blow cool air from a lower part of the house up through the vents. I called the company that installed mine bu they said it would be $150 to install a switch. The guy I talked to said he has that option on his house and it works great.
Keeping that in mind, last year - having nothing to do with the above - a little 6" rubber hose wore out on my furnace and there was a safety mechanism that prevented the heater/flames from going on but the fan kept going blowing cool air through the house. It took a few days for me to figure it out what the problem was - I just bought a rubber hose from an auto store and it works fine now. My thought is that I could just remove that rubber hose which would shut off the heat/flames but allow the blower to blow. Would that be safe? Or is there any other advice. $150 would normally not be a lot, but times are tight for everyone.