My heater only blows hot on the passenger side

Does the vehicle have dual zone climate control, where the driver side and passenger side have different control? Sounds like a blend door issue on the driver side. Why did you replace the passenger side, was it blowing hot too when AC was on?

You have actuators which direct the air in the heater/vent/AC system. My first cars used metal cables, then came along vacuum line control and most now use electric control actuators. They control things such as how much air from outside the car come inside, air flow to windshield/floor or dash, control mix of air for temperature adjustment. Your problem more than likely actuator issue. You can try google vehicle year, make, model temperature different from ac vent, when search you can change wording. If vehicle is older and used vacuum lines could have line leak, my 2000 GM van once had vacuum line laying on engine melted line and leaked. My 13 Chrysler, I have changed 2 actuators they are controlled by electric and started clicking when they went bad.

DODGE DART, CHRYSLER 200 CAR BLOWS HOT ON DRIVER SIDE COLD ON PASSENGER OR COLD ON DRIVER SIDE - YouTube

Very possible you have AC Control Head issue. You don't want to guess by putting parts on. Try unplugging control head for a few minutes, then see if it reacts different.

Heater or mode door actuator bad , possibly ! You can look on youtube for videos showing how to change . It can be easy or very hard to replace . You could have it checked for DTC's diagnostic trouble codes stored in the heater control head . dealer only !

Check behind heater control for vacume leak to actuator or use a vac. pump on the actuator to see a difference.

I assume this truck has daul zone heating and a/c, the air blows but is not hot? if this is the case then you may have dissconnected the blend door actuator or it just went bad. this is common that the actuator goes bad,
there are two seperate actuators that control the hot/cold door in the heater box this way the passenger and driver can set there on temp.
the actuator for the drivers side is locted on the drivers side under the dash on heater box, the blower is on the passenger side , you can check connections but i do not think it is that but rather the actuator.

Check operation of passenger side air direction deflector vane in the heater ducting.
You may have a seized vane hinge or faulty actuating servo/control.

you need to change drivers side temp door actuator then disconnect battery for 5 seconds and reconnect after changing the part, turn key on for 60 seconds with touching heater control to allow actuator to program and then it will work.

There is a flap inside the vent. It is controlled by a vacuum controlled actuator. Either the flap is stuck in one position, or the the actuator is faulty. Check vacuum lines to actuator.

As long as you did not have to go into the dash to splice those wires, I would say that you have either a Tempreture door that is Broken, or the actuator that controls the passenger side temp. door is bad. Most likely cause will be the actuator, because they have a very high failure rate. The actuator is located is located on the very top of the a/c-heater box behind the radio and a/c control head. It will be rather hard to change because every thing fits so tight. But if you remove the radio and the A/c control head you should be able to find it. Let me know if you need further assistance.

I’m happy to assist further over the phone at https://www.6ya.com/expert/jonathan_3a3c556b4b17d1d2