The cooling/heating system temperature control lever for the driver's side on the dash must be held down tight in order for cool air, rather than heated hot air to come out the vents.
Rheostat is bad you need a new control module. As you slide the control it makes contact with a resistor that changes resistance depending on location. If it is working by forcing it then its either loose on the inside and the forcing is making contact or the resistor is bad and forcing it just past its normal rest spot is getting it into a good section of resistor. Either way its broken and needs replaced.
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