* Electrical Short Circuit: This is the most probable cause. The smell of smoke strongly suggests overheating wiring within the climate control unit itself, possibly in the blower motor resistor, the control module, or other wiring harnesses connected to it. A short circuit could occur while the system is running (drawing power) or even after it's switched off if there's a residual charge in a capacitor or a fault that persists even with the power off.
* Overheating Blower Motor: Though less likely to cause smoke *from a vent*, a seized or severely worn-out blower motor could overheat and melt its own wiring or surrounding components, potentially leading to smoke.
* Overheating Resistor: The blower motor resistor regulates the fan speeds. If it fails, it can overheat and burn, causing smoke.
* Other Electrical Component Failure: There are many other electrical components within the climate control system (relays, fuses, etc.). A failure in any of these could potentially lead to overheating and smoke.
* Something caught in the blower: While less likely to produce smoke *from* a vent, a highly flammable material lodged deep within the system could ignite and cause smoke. This is less likely given your description of smoke coming from the vent specifically.
What you should NOT do:
* Don't continue to use the climate control system. This could worsen the damage and potentially cause a fire.
* Don't try to diagnose and repair the problem yourself unless you have significant experience with automotive electrical systems. Working with electrical systems without proper knowledge and safety precautions can be very dangerous.
What you SHOULD do:
* Immediately disconnect the battery's negative terminal. This will prevent further damage and reduce the risk of fire.
* Have the vehicle inspected by a qualified mechanic. They have the tools and expertise to safely diagnose and repair the problem. Do not attempt to use the climate control system until it's been fixed.
* Describe the situation clearly to the mechanic. Tell them about the smoke, when it happened (running and off), and the location (specific vent).
Ignoring this could lead to a much more serious and expensive repair, or even a fire hazard. Professional help is necessary.
