2006 Murano Heater Problem



the heater is malfunctioning in my 2006 Murano SE that has dual driver/passenger temperature controls. After starting the vehicle from a cold soak and after the engine temperature gage shows the engine has warmed up, the heater blower comes on but blows cold air. This continues for some time (~15 minutes) and then the heater will start blowing warm-hot air. The problem is worse at colder tempaeratures. But the heater will often blow hot air after warm soak start-up. Could the problem be as simple as changing the engine thermostat, or is it a problem with the heater controller or something else? Thanks.