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Q: What causes the heat to change over to cold when van is running? have had everything checked, all working 2005 Chrysler Town & Country

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When I start the van, and turn on the heat/defrost, it will start out warm/hot, then when driving it turns cold, and will not change back to hot, have had it checked at an electrical auto shop, they could not find anything, said it may need flushed, but when I called to see about that, the other place said that flushing wouldn't help it. Can you help? Have had a couple people say that it sounded like the temperature door
My car has an automatic transmission.

Hello - the first task is to verify that the engine is maintaining designed operating temperature so that you have a consistent heat source. This is easily verified by making sure the temperature gauge stays dead center. If it isn’t, you may have a thermostat that is weak, and needs to be replaced in order to keep the engine at operating temperature. With consistent hot engine temperature, check for heat on any function - heat, defrost, etc. If there is heat for some functions consistently, but not for the heater, the heater flap controls are malfunctioning. When the heater goes cold, and all other HVAC functions (defrost) are also cold; either the heater control valve, or the heater control switch is failing to let hot water into the heater core. I would recommend an inspection of the heater by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.

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