I have a 2007 grand caravan heater gauge goes up 3/4 of
the way. Has not overheated. Blows out cold air. Began
to heat only passenger side. Replaced thermostat and
radiator cap. Still no heat. Ran air conditioner motor runs
heat runs help
Purge the air out of the system and make sure the radiator is full of coolant. https://www.youtube.com/watch?v=zUpXgAJ1gjU
Plus also check your mode control doors for the HVAC unit it may not be switching or you have a broken door inside the heater box itself.
Heating only on one side would likely indicate that one of the sliding controls of the "dual zone temp control" has failed. Unfortunately, this is a $600-$650 part - dealer only. You should be able to find a used one somewhere for $40 or so. This is very easily replaced, if you are at all mechanical - ten minutes. I just replaced one. The passenger side controls the rear heater temp, so check to confirm that that is being heated. Sometimes you can slide the failing slider back and forth a few times and find a spot somewhere that will still give some heat to get by for a while, but not forever.
https://www.ifixit.com/Answers/View/94848/fan+w orks+but+no+heat+comes+into+cabin.+Troublesho oting+ideas Is s know issue with the flap blender door. 2001- 2007
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