DMax Heater Issues: Defrost Flap & HVAC Troubleshooting

Had a similar issue with my 2005 D-Max back then. The symptoms match exactly what I experienced, poor heat and constant windshield fogging. The blower motor seemed to work, but air distribution was completely messed up. Took it to my workshop where they found a loose connector affecting the air distribution flap motor. The temperature regulation was going crazy because of this faulty connection. Total repair was 95 Euro, mainly labor costs for tracking down and fixing the cable connection. Been working perfectly since then, no more heater core issues or fogging problems. These systems can be tricky to diagnose without proper testing equipment. What's your current mileage and have you noticed any strange sounds from behind the dash when changing temperature settings? Also, when did you first notice the heating problems, was it gradual or sudden?

Thanks for the detailed response. I'm at 20697 KM since my last major service. The ventilation system problems started about two weeks ago pretty suddenly, one morning the climate control just wasn't responding normally. And yes, I'm definitely hearing some clicking sounds behind the dash when adjusting temperature settings, especially when switching between defrost and normal modes. The blower motor seems to run fine, but the air flow is really inconsistent. Based on what you're describing, I should probably have them check those flap motor connections first before assuming it's a bigger heater core issue. I was worried I'd need the whole HVAC unit replaced. Did your mechanic have to remove the entire dash to access those connections, or was it accessible from underneath?

Yeah, those symptoms are nearly identical to what I experienced with my D-Max. The sudden onset and clicking sounds pretty much confirm what I suspected, it's most likely the flap motor connection issue. The good news is my mechanic didn't need to remove the entire dash. They accessed it from underneath through the lower dash panel. The air circulation problems and inconsistent temperature were happening because the flap wasn't moving properly to direct airflow where it should. When the connection is loose, the HVAC unit can't properly control air distribution, which explains both the poor heating and windshield fogging you're experiencing. Quick tip, while they're in there checking the connections, have them inspect the entire air distribution system. My mechanic found some debris that had worked its way into the housing over time, which was also affecting the flap movement. Since you're at 20697 KM, it's about the same mileage when mine started acting up. These connection issues seem to be a common wear point in these models. The repair should be pretty straightforward, mine was back on the road the same day with perfect heat output and no more strange noises.

Thanks for that helpful insight. Glad to hear they can access it through the lower dash panel, that should keep labor costs down. The clicking noise from the dashboard panel makes more sense now, knowing it's likely just a connection problem affecting the air circulation system. I'll definitely have them do a full inspection of the distribution system while they're working on the flap motor connections. After dealing with this windshield fogging and weak heat output for two weeks, I'm ready to get it sorted. The climate control issues are really starting to get annoying, especially since the blower motor seems fine but the air just isn't going where it should. Going to schedule the repair for next week. Really appreciate everyone's input, helped me avoid potentially unnecessary heater core replacement costs by identifying the more likely culprit. Will update once it's fixed.