Front AC blower fan only works on when thermostat is set to higher temperatures, and slows to a stop when set to colder temperatures.

After working through some overheating issues that seem to be a result of air in the coolant hoses, I have come across and issue with the front climate control system. Part of my troubleshooting for the overheating involved setting the climate control temperature to full heat and low fan. The system seems to operate fine at this setting. This afternoon on my way home from work, I turned the air to a colder setting. I get cold air for a brief period, maybe 30-45 seconds. Then over the course of about 30 seconds the blower fan slowed down until coming to almost a complete stop.

If I set the thermostat back to warmer temperatures, after about 30 seconds, the fan will start to speed back up. This happens even with manual fan speed operation. This is not a result of leaving the system in auto mode, and only adjusting temperature. I am able to replicate this problem by switching back and forth between hot and colder temperature settings.

Could this by-product of overheating caused by low coolant/air in the system? Any ideas on next steps for fixing this?

 

You also have the output location set to manual too and to just one such as dash vents? Because the fan can certainly sound different when being output to different locations. HVAC operation is independent of the cooling system other than using coolant for heat.

 

That is correct. Changing the output location has no impact. There is a noticeable slow down to a stop of the blower fan when temperature settings or set to cold.

 

If you have access to a good code reader* that also can show live values it might help. From experience I know that you can get a lot of telemetry from the car, like temperatures and fan rpms but also position of the blender doors. I don’t have a better idea where to start, unfortunately.



*) I have an IIDtool but there are probably others