Honeywell Thermostat Blowing Cold Air. A dirty air filter blocks airflow over the furnace's heat exchanger, causing it to overheat. I bought a honeywell t5 but when in the heating mode it blows cold air.

4) issues with thermostat wiring. Check the thermostat's display to confirm that there's a call for cooling, usually indicated by the words cool on or a snowflake icon. Most honeywell thermostats blink when in a time delay for the cooling (or heating if it's a heat pump).