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Hi, your vents are vacuum operated. For the vent problem you are going to need to have the vacuum system checked for leaks. Any leakage in the system and the vents will default to defrost. On your erratic temperature control you are going to need to have the temperature sensors in the system checked. It sounds like you may have a fault in one of the sensors and the system cannot regulate properly. On your blower problem you have a shorted electronic blower regulator. When the regulator shorts out it causes the blower motor to run on high, even with the key off.
So, it sounds like I have 3 distinctly different problems. I was hoping this all led to a single problem. Thanks!