It has dual heating and cooling. The air is on

DTC B1340 Air Mix Door #1 Movement Problem !
The heater and A/C programmer supplies voltage to an internal motor that drives the air mix door. The heater and A/C programmer monitors the air mix door position feedback from a sensor on the motor. If the air mix door is requested to move but the feedback voltage does not change, the heater and A/C programmer will store DTC B1340. If the air mix door feedback indicates that the feedback is near the hot or the cold extreme, the DTC will not set. Evaluate the operation of the air mix door through self diagnostics as described in the test description.
Test Description
Perform the Diagnostic System Check before continuing with the diagnosis of this DTC.
A Scan Tool allows for the direct control of the air mix door by observing the following conditions:
• The air mix door position feedback value
• The value`s difference from the air mix door commanded position value
These readings indicate a fault internal to the heater and A/C programmer in the air mix door sensor feedback.

Did you perform the Diagnostic System Check?
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Go to Step 2
Go to Diagnostic System Check
2
With the engine running, connect a Scan Tool .
Turn the dual zone to OFF (passenger temperature offset at 0 or OFF).
Exercise the suspect actuator using the temperature control on the control assembly.
Is the door being commanded (COM) to the proper high and low values?
COM High 100 %
COM Low 0 %
Go to Step 3
Go to Step 4

If you are unfamilier with this , i suggest you take it to a ASE certified repair shop or the dealer .

There has to be a blockage in the duct work to that side of the vehicle.

First....buy a drivers side air flow actuator at a auto parts place for dual zone heating/cooling.
(NAPA etc will have it.....or the dealer)
Open the glove compartment.....all the way....you may have to take the screws out at the bottom......look in at the heater assembly....look over to the left....you will see the two air flow actuators.
Look at the part you have and match it to the part on the heater assembly.
The actuator that is closest to the engine is the drivers side control.
Replace it.
Try your controls and check for heat and cooling on both sides.
The stepper motor in these actuators goes bad on quite a few...but over look that.....you have a great car,good for many miles of trouble free driving.

Do you have dual zone heat and cooling controls?
If so......the drivers side air flow control unit on the heater assembly is not working.
It is mounted on the heater assembly and can usually be accessed through the glove compartment to change it.
The stepper motor on these units fails often.
This should be the problem on your car 99%...if you have a separate heat/cooling control for driver and passenger areas.

Hello. The side that is not operating properly has a bad temp door actuator located up under the dash. I am assuming this vehicle has driver/passenger(dual)climate control heat and cold settings. This is a very common problem on these vehicles. Hope you find this information useful!

The thermostat adjustment control may need to be replaced. Also check the hose on the back for cracks, clogs, or missing.

I had the same problem when i was working on my 1999 Buick Regal and had to disconnect the battery. I didn't reconnect in the same way that I disconnected the battery from the terminal and noticed that the driver side had no heat or air but the passenger side did. I then disconnected the battery again and reconnected it the same way and now have heat and air on both the driver and passenger side. Hope this helps. Good Luck!

Most likely the blend door motor is defective.

Is it leaking antefreeze?
The thermostat might be gone or needs a bigger thermostat
It could be a vaccum leak for the drivers side blowing cool air and the passenger side blowing warm air
Does it have dual air control switches one for drivers side and one for passengers side?