It was in the low 50s this morning so I turned on the "Auto" function and set the temp to 70 which usually warms the interior up. Only cool air blew from the vents. We recently replaced the "coolant flow control valve" and had to add some coolant at the time but I never follow up checked it so I'll do that this evening. Any other thing to look at when diagnosing a problem with no heat?
A coolant control valve can get stuck in a position that cuts off coolant flow through the heater core, so that can be a cause. The air mix door can get stuck in a position that cuts off air flow through the heater core, so that can be a cause. For people of typical flexibility, it isn't too hard to peek under the dash and see if the air mix door moves.
Thanks pal. This is my daughter's car and I've been driving it for the past few weeks. She just informed me that it's been doing this for years so I'm gonna guess it's probably not the flow control valve since it's been replaced twice in the last two years and once about 3 months ago. Gonna check the blend door.
also check the heater core lines going through the fire wall. Both should be warm, if coolant is circulating throughout the heater core. If both hoses are warm, I'd look at the blend doors. If one or both lines are cool to the touch; you have no coolant flow. At this point, you'll need to troubleshoot why coolant isn't flowing. Coolant bleed issue, control valve issue, clogged heater core, coolant pump issue. Good Luck....
