why would only the driver side blow heat through the vent and defrost and on the passenger side is blowing cold air?
a diverter or servo motor is malfunctioning~ will have to research on part numbers and mechanisms if you need~
are you hearing any hissing? possibly a vacuum hose is cracked or fallen off~
my 1994 deville was the opposite - warmish on passenger side defrost and cool on drivers side. Turned out to be a problem with an inexpensive plastic " T " that (on my car) is top and center near firewall under the hood. too much hot water was going thru the bottom of the T and not enough going thru firewall to heater core. $20.00 part fixed it!
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