Heater problem RENAULT Trafic III Van (FG_)

Your issue with the 2014 Renault Trafic Mk3 blowing hot air on the passenger side and cold on the driver side, and reversing when the AC is on, is most likely caused by one of two common problems:

1. Faulty Blending Flaps (Blend Door Actuators)
- The blending flaps inside the HVAC system control air mix and direction for driver and passenger sides.
- If a flap or servo motor is stuck, misaligned, or broken, it can cause uneven heating/cooling distribution.
- Symptoms match your description where one side blows hot air and the other cold.
- Check for any fault codes from HVAC system if you have a diagnostic tool.
- Sometimes flaps can be repaired or replaced individually, but it usually requires removing the dashboard or glovebox panel.

2. Blocked or Faulty Heater Matrix (Heater Core)
- The heater matrix (heater core) transfers heat from engine coolant to the cabin air.
- If part of the matrix is clogged or partially blocked, it can cause uneven heating.
- Coolant flow may be restricted on one side, resulting in cold air there.
- Flushing or replacing the heater matrix can resolve this.
- Warning signs also include reduced heating output overall and coolant leaks near the firewall.

What to Do Next:
- Start by checking blending flap servo operation and related fuses.
- Use diagnostic tools to check for HVAC error codes.
- Inspect coolant levels and ensure proper circulation.
- If flaps are fine, consider flushing or inspecting the heater matrix for blockages.
- If unsure, seek professional inspection as both repairs can be labor-intensive.

In summary, uneven heat on driver and passenger sides often points to blending flap faults or heater matrix problems. Diagnose the flaps first and clean or replace the heater matrix if needed.