Simple question I think, but you guys make the call.

Can the cooling wire (Y) be used to activate the furnace fan?

My neighbor has a Honeywell RTH7400 programmable thermostat used for natural gas heat with fan only (he has no AC). I've already figured out how to turn the fan on manually, and that's OK.

I, however, was wondering if the cooling contact on the t-stat can be used to turn the fan on automatically if I set the t-stat to be a Heat and AC system.

The t-stat is presently set to 'heat only with fan'.
Only reason I ask is 'cause I don't want to ruin anything.

Thanks in advance. I appreciate your input.