* Leaking Heater Core: This is the most common culprit. The heater core is a small radiator located inside the dashboard that heats the air blown through the vents. A leak allows coolant (which turns to steam when hot) to escape into the ventilation system. You'll likely notice a sweet smell (antifreeze) and possibly a loss of coolant from the radiator over time.
* Clogged Drain: The AC system has a drain to remove condensation. If this drain is clogged, the water can back up and potentially mix with coolant or seep into the ventilation system, appearing as steam. This is less likely to produce a sweet smell.
* Condensation (less likely with "steam"): In cold weather, condensation is normal. However, significant amounts of visible *steam* rather than just condensation usually points to a coolant leak.
What to do:
1. Check your coolant level: Open the hood and locate the radiator and coolant overflow tank. Check the levels. Low coolant strongly suggests a leak.
2. Inspect for leaks: Carefully examine the radiator, hoses, and connections for any signs of leaks.
3. Smell the air: If you smell something sweet, it's almost certainly antifreeze from a heater core leak.
4. Professional diagnosis: If you suspect a heater core leak, it's best to take your truck to a mechanic. Replacing a heater core is a relatively involved job, often requiring partial or complete dashboard disassembly. Attempting it yourself can be challenging.
Ignoring the problem is risky: Losing coolant can cause engine overheating and significant damage. Addressing this issue promptly is crucial.
