Cheap Thermostat Issues?

[prufrok]

Hello, I replaced an aging thermostat with the cheapest one I could find at home depot that accommodated heating and cooling ( honeywell rth2300/rth221 ). I have it programmed for 18 during the day then 20 in the evening. i notice AFTER it reaches the evening warmer temp it then blows cold air. given the time of year i cant tell if its AC air or just unheated air. is it a dumb thermostat that thinks it not has to cool? is it trying to not let temp go any higher, just a bad one, anything else?

[Admin]

You should probably look outside the next time this happens and see if the air conditioner is running.

Your house may also have an HRV or bathroom fan interlocked with the furnace fan which would cause unheated air to blow throughout the house when they are running.

Make sure the thermostat fan is set to AUTO and not ON.