Seen online if got air in system it would cause this.
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2003 Nissan Altima Question: Heater blowing cold air! Changed termostates. No help
Answer #1gmc4me January 09, 2013, 18:36Journeyman
If there is air in the system the waterpump will not pump the coolant throughout. You may have air in the system and need to bleed it out, could be a bad temp./blend door actuator which moves a plastic flap inside HVAC box when you adjust the temp. at the controls, could possibly be a clogged heater core, or your new thermostate could be bad. Especially if it's aftermarket. I've seen a couple new aftermarket thermostats go bad in a week or so after installing them.
Replymikeyb4, January 09, 2013, 18:44Rookie