The most popular season in Michigan is summer. According to a survey of residents, it's followed by fall, spring, and winter. The extreme cold and sub-freezing temperatures might be the reason winter ranks last on the list. Thankfully, a working HVAC system can ensure you're comfortable regardless of the temperature outside. It should provide proper ventilation to reduce humidity and regulate indoor temperatures. It also helps to remove contaminants in the air to maintain indoor air quality. f your HVAC fan won't turn off, these functions can be compromised. Certain signs will indicate if this is the case. It's important to know what they are, why they may be happening, and how to fix the problem.