Sometimes the moisture can build up because a drain is clogged. A technician can clean that out and get things draining again. If the vapor coming out of the vents has a sweet, syrupy smell, it could be caused by a hole in your heater core. The heater core is the part that helps heat the cabin in colder weather.
A leak in the heater core can lead to vapor when the a/c is running, they share a chamber. This is mostly likely condensation, but a coolant leak is possible.
Absolutely normal. Once you have your A/C going, the air in your vents is going to be cool and dry. By turning the A/C off, you allowed the vents to be filled with warm, humid outside air. Turning the A/C back on will force the humid air to condense rapidly... the result is the fog coming from your vents.
The cause of sweating vents is simple. Air that's humid enough finds a surface cold enough. When vents start beading up with water--or worse, dripping--either the humidity is too high or the vent is too cold. It's not hard to figure out which of those two is the culprit. Just find the dew point of your indoor air.
Sometimes it can be caused by water accumulating in the vent system after it condenses. That water can wind up at the bottom of a vent, and when you turn on the blower motor, it can cause what looks like steam or vapor to come out of the vents.
It is common for the white fog to form when cold air collides with warm air (that's highly humid). This can be likened to when you go out on a cold day, and your breath is visible.
A drip or two of water leaking from under your car is normal, but if it is increasing in frequency and volume, your car needs to be checked.
A warning sign that your car's condensate drain might be blocked is when you notice the water leaking inside your vehicle. If you find your car's floor getting wet with water whenever you turn your car's air conditioner on, then it's time to check your condensate drain.
The purpose of the drain hole in air conditioners is to allow condensation to escape. However, over time, dust and debris can build up causing a blockage. This leads to backed-up condensation in the air conditioner which then gets released as a mist or fog from the AC vents.
Running the Car Heater with the Air Conditioning On
Running your car's heater with the air conditioning on might sound counterintuitive, but it works wonders for drying out the interior. The heater warms the air, helping to evaporate moisture, while the air conditioning unit dehumidifies the air by removing humidity.
“The odorless steam coming from the vent is possibly excess water accumulating in the heater box, which may indicate the drain hole is restricted and needing cleaned.” Dave Carney, president of Hillside Auto Repair in Torrance, said the problem usually occurs in older cars.
The AC Condenser Coils Need to Be Cleaned
Over time, these coils can become clogged with dirt, dust, debris, plant matter, and more. This build-up of contaminants can prevent the coils from doing their job properly, resulting in humid air being blown into your home instead of cool and dry air.
When your car sits outside, especially overnight, condensation can build up inside of the exhaust system. Starting your car will warm that condensation, turning it into steam. As the exhaust system warms up, the condensation will disappear, and the white steam along with it.
To clean your car's AC, turn off the engine, and let it cool. Clean or replace the air filter, wipe vents with detergent, vacuum debris, and spray cleaner. Run AC to circulate the cleaner.
Typical unclog ac drain line costs can range anywhere from $75-$250. In the case that the evaporator coil needs replacing, you are would pay between $400 to $950.
Freon Leak
A lack of cold air blowing through your vents could have a number of culprits, but the simplest and most common explanation is a lack of refrigerant. Many times, this is caused by a Freon leak due to a failed O-ring, seal or hose. Discovering these leaks early is important.
The condensation collected by your air conditioner carries the dust and debris into your drain line and your drip pan. Eventually, the drain line can clog, causing water to back up and eventually leak. The same thing can happen in the drain pan: dust can clog the drain, causing the pan to overflow.
If you suspect that your condensate drain is blocked and feel confident in identifying the right parts under the bonnet, you can gently unblock it by locating the condensate drain hose (usually at the read of the engine on the passenger side) and squeezing or maneuvering it to release any debris or blockage.
When you see water leaking inside your vehicle, it is a sign that there is a blockage in your car's condensate drain pipe. You will frequently find the car floor getting wet as the condensate pipe drain's water inside, and the blockage prevents it from draining water outside the car.
If the air temperature near the appliance is below the dew point, this causes water vapor to form in the air and condense into water droplets, thus causing the fog or smoke. A dirty air filter or low fan speed may aggravate the condition.
Worried about that fog or the mist you see coming from your AC? Don't worry—it usually doesn't mean there's something wrong with your air conditioner. The mist is just condensed water vapor that forms when cold, dry air comes into contact with humid, warm air (we'll explain this in more detail later on).
Sometimes it can be caused by water accumulating in the vent system after it condenses. That water can wind up at the bottom of a vent, and when you turn on the blower motor, it can cause what looks like steam or vapor to come out of the vents.