Cadillac Catera 98 drivers side heat not working. Passengers heat is good but drivers is just cold air. Defrost is the same way. How can I manually correct this for the winter. The air conditioning broke this last summer.

The water valve is stuck open. Water valve should be off for A/C function.

For each side of the vehicle, there is an air mixing valve buried inside the dash and controlled by an electric actuator. This can be a very complicated problem because the HVAC control system in this car is complicated. First step would be to use a code scanner to see if any error codes (DTC's) are set and proceed from there. If codes are set, you can try disconnecting the negative lead on the battery and then reconnecting it a few minutes later. If that doesn't work, determining the problem and fixing it is a job for a dealership.

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?
--
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 .

you probably have an issue with the 'blend door', a common problem on Caddys-the arm can (and does) break, removing the ability to change from cold to hot air...check first to see if the vacuum line (very narrow) that goes from the top of the engine into the passenger side of the firewall is not disconnected or broken/frayed. The only other possibility beside this or the blend door is the controller itself-they also can fail, or have problems in the circuit boards or vacuum leaks back behind them. Look for the easy one first-the vacuum line is the most common reason.

your heater core is probably leaking

The first issue is to reprogram the blend doors for the HVAC system. You can do this yourself by pressing on the Off/On button and the drivers side temperature control knob at the same time for five seconds. Then release the buttons and you should hear the doors moving as the system reprograms itself. Good Luck.

could be low on freon

the leveling light wont shut off because the compressor is running and trying 2 fill up the rear air shocks that are probably popped

THIS PROBLEM OF NO HEAT IS CAUSED BY A FAILED AC/HEATER AIR TEMPERATURE CONTROL BLEND DOOR OR BY THE MOTORIZED ACTUATOR THAT MOVES THAT DOOR, THESE ARE THE ONLY PARTS THAT CAN CAUSE THIS PROBLEM, WHICH IS COMMON IN LATE MODEL CARS SINCE THE 90'S, THE REAL PROBLEM IS THAT THE DASH MUST BE REMOVED FROM THE CAR TO ACCESS THESE PARTS.

The most likely cause of your problem is the blend doors under your dash. If they are not moving like they should it can cause this type of problem. You can look under the dash to see if there are any linkages that are disconnected. Some of these are very hard to change so you might want to take it to a repair shop unless you are very good with cars.