Sounds like the blue car has a bad monovalve. This is a common issue, and there is lots of info on repair if you search the forums. When the rubber seal fails, the monovalve stays open, and hot water goes to the heater which causes the cold AC to get warmer. Not sure why you still have cool air inside. Anyway, the fix is a new monovalve kit. Inexpensive, and a pretty straight forward job as it is accessible. You need to pinch rubber hoses with visegrips so coolant does not come out. The top of the valve body has a connector that comes off, and the plate is removed with 4 screws. Remove it slowly and note the position of the parts and the wavy spring washer. The solenoid is usually Ok, but the sealed valve assembly is what gets replaced. Make sure the heavy metal ring component goes back right, as I think it has a notch. Kit is available from online parts guys. Original part is Bosch, but many others are around.