2005 Pacifica, intermittent heat.
 

Hi guys.

My parents have a 2005 Pacifica. Lately, they've been having an issue with intermittent heat. The fan works in all settings. They've reset the system, that didnt work. Brought it up to the dealership, no codes showed up. Coolant is full.

Some times it'll cook them out of the car, then suddenly blow ice cold air. Then all of a sudden start working again.

Think it is some kind of a valve or electronic piece having an issue?

Thanks, Matt