This time of year we get allot of furnace service calls. Most of them are complaints that the furnace is just blowing cold air. This is typically a safety feature feature that has either malfunctioned, or is working just fine. The main safety feature that does this is called a high limit control, this device keeps the internal temperature of the furnace from getting to hot. If the furnace overheats the limit switch will recognize the problem and shut off the burners leaving the blower on. This allows the furnace to cool back down. On some furnaces if the limit switch is activated for more than three minutes it will lock out the furnace for three hours. The easiest way to diagnose this is to shut the power off to the furnace and turn it back on, of this fixes it for a few moments, than this is the problem.
You can prevent these problems from changing your filter on a regular basis. If you have a one inch thick filter I recommend changing your filter on a monthly basis. (even of the package says longer) If you have gone a long time without changing your filter and this problem persists, you might need a tune up, or a repair. A tune up will allow us to go inside the furnace and clean out the blower, adjust the gas input and make sure everything is running smooth. Good luck, and let us know if we can help out in any way.
