Passenger side of 2000 eldorado blows cold air and driver side blows hot, told this is due to blend air door motor is out of synch

The most common cause of this is that you have a stuck air temperature control blend door, this can be a motor actuator issue or a jammed door or both (common). To replace both parts you will need to completely remove the dash from the car to access the blend door.

here is a link to a fault finding procedure

Your system is either out of sync on the control, or the air temperature control blend door is not moving due a failure of the door or its actuator motor.

Usually a blend door problem, either the control or the blend door itself.

Usually a blend door problem.
Doors under the dash direct air thru the system.

This problem is likely due to a failed part called the blend door, this door has an electric motor drive, to replace it requires the dash be removed form the car entirely. The blend door is a door that moves back and forth between the AC core and the Heater core to provide cold hot or a blend of air flows from both cores to give the desired temperature. Other issues can cause this and due to the cost or repair a through diagnostic should be done to confirm my guess is correct about the door being the problem.

There are separate blend doors for the passenger and driver's side. The blend doors divert, not block air, so it is unlikely that the blend doors are the problem. Your mechanic needs to check the operation of the re-circ door and if its fault replace it.Thanks. Hope you rate my response

You need to replace the "blend" door actuator motor on the pass side. I recommend getting that from your nearest gm dealer to ensure proper fit. When you adjust the air from cold to warm to hot, the blend door moves to direct the right amount of cold, or warm, or hot air your desire on that side of the vehicle

common problem, you have a bad blend door motor, also be careful sometimes the blend door breaks at the end that goes into blend motor if is then blend door has to be replaced also w/motor hope this helps, ive done a lot of these, good luck.

This is either an out of phase issue or a temperature control blend door or blend door motor actuator problem, it can also be the climate control module in the dash, 1st try disconnecting the battery for 5 min's to re-sync the climate control module, if this fails u will need to find out what blend door is the problem or if they are ok replace the automatic climate control module in the dash