We are now in the winter up here in CNY so this problem wouldn't occur until now. It seems that our furnace is cycling on on and off more frequently than in the past. We installed an AC unit this summer and was wondering now that the evap coil sits atop the frunace in a insulated box, would this cause the unit to retain its heat making the limit switch start another "cool down period" where the fan comes without the burner. I sat and watched the whole operation this morning and that seems to be what I'm seeing. My wife swears something is broken and I say it is just cooling itself off. Any help would be appreciated.:) Plus other than the fan running more than often how could this effect our heating bill? Just increased electricity costs I say.:eek:

If you have a drum type heat exchanger (usually a oil furnace) misplacement of the evaporator coil can cause a problem with heat retention. If the coil sits right on top of the drum it blocks air flow which in turn keeps heat in the furnace. This can cause the high limit to come into action and cause the burner to shut down for a cooling down period. I would have this checked before you continue to operate in this condition.

I have a natural gas fired furnace. I don't know if your answer still pertains to this or not. The coil cabinet was made to go ontop of the furnace. Wich is a tempstar furnace and ac unit.I recently change the thermostat, this also needed to be adjusted (temp swing, temp offset) bumped it up a couple of numbers and it seems to be not running so often.
Thanks for the help

Good deal you probably have found the problem. You never mentioned a new thermostat in your post.

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Originally Posted by hvac1000

Good deal you probably have found the problem. You never mentioned a new thermostat in your post.

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Sorry:o