[masraum]

I've got an older (1967) 2 story house in Houston (HOT & HUMID in the summer).
The house is a tract house. Both floors are divided into 4 rooms with stairs in the middle. When you open the windows, especially upstairs, you may not get a fraction of the breeze that you feel outside in the house. It just wasn't designed to have air flow through the house.

I've opened the house when it was 68* outside and 72* inside and actually had the temp go UP inside the house because of lack of air flow.

That's the background.

I've got a regular gas furnace and A/C unit (not a heat pump, no dual level, nothing special) with a 7 day programmable thermostat that will auto switch heat <-> cool.

During the comfortable months, the temp downstairs can stay low enough that the A/C never kicks on, but the upstairs can end up 5-10 degrees warmer.

I'd like to set up a couple of temp sensors (one up and one downstairs) connected to a spare computer and setup a program that says "if the temp differential between the up and downstairs exceeds X, turn the fan on." Assuming that I can work out the temp sensors (easy) and the program (not so easy for me), how would I connect the two without frying anything.

It's my understanding that the green wire is the fan and I just have to join that to power(red wire) to kick the fan on. I assume that proper placement of a few diodes would also be necessary. I'd like to tackle this, and was wondering if anyone of you electronics gurus had any thoughts.

Thanks