Just googled the 99-7803g kit and see the setup. It looks like it has its own climate control panel.

I'm looking at the factory shop manual to give you some electrical tests to try. Is your car a 4 or 2 door? It makes a difference on the pins/wire colors on the air mix motors.

 

Sedan ex-l with dual climate control

 

I'm having a similar problem my ac works on both side & it switches modes fine but the heat doesn't work on my drivers side only. I've replaced the blend door actuator & still nothing. It's like it's not rotating enough to push the heat door up

 

If you remove the blend door and manually push that lever, does the heat work on the driver's side?