Lukewarm air on passenger side?

With winter on its way the heater is definitely needed. If the passenger side blend door actuator goes out it will cause this problem, I assume the driver's side is hot, correct? Here is the location of the blend door actuator so you can swap it out.

The Dual Zone heating and A/C system has two blend door actuators, one for the driver side and one for the passenger side.

Here are both the drivers' side and passenger side actuators so you don't get them mixed up. Also, you will need to remove the glove box and some ducting. Check out the images (below). Please let us know how it goes.

Yes, it could be, is the driver's side hot or lukewarm as well? With the engine warm grasp, the heater hoses going into the firewall to check the heat level. Also, check the coolant level of the system when it is cold only. If the heater hoses are not hot here is how to change the thermostat out. Please check out this guide as well:
https://www.2carpros.com/articles/car-heater-not-working

Here is a generic guide to help you step by step with instructions in the diagrams below to show you how on your car.

https://www.2carpros.com/articles/replace-thermostat

Check out the images (below). Please let us know how it goes.