You probably do not give much thought to your HVAC system until it stops working. When your air conditioner gives out on the hottest day of the year or your furnace refuses to turn on in the middle of winter, those are the times you worry about your HVAC system.

Waiting until your air conditioner blows hot air or your furnace runs cold is counterproductive and expensive, so why not be proactive about your HVAC performance? Your HVAC system is designed to keep your home comfortable no matter how hot or cold temperatures get. These systems rarely fail in a surprising way. Most of the time, your HVAC system will give you ample notice that it is about to give up the ghost. Here are some HVAC warning signs you should never ignore.

Unusual Odors

If your HVAC system is running the way it should, you will barely notice it. You might hear a small noise as the furnace kicks on or the air conditioner gets going, but the HVAC system should be pretty unobtrusive.

The presence of unusual smells should be cause for concern, so pay attention and use your nose as a diagnostic tool. The smell of decay, for instance, could be caused by a rodent or other small animal that died after getting trapped in your pipes or ductwork. Leaking fluids could cause the smell of exhaust, and a burning odor could be the result of a compromised AC compressor or fan. If you smell the gunpowder, you could be looking at a blown circuit board or a bad fan motor. Sometimes the most dangerous system malfunctions are not accompanied by an offensive smell. Bill Leech, a founder of Summit Heating and Air Conditioning, encourages homeowners to, "install and test carbon monoxide sensors on a regular basis."

If you detect any of these smells, you should turn off your HVAC system right away. Allowing your HVAC system to run in a compromised state will make the damage worse, and that could mean a bigger repair bill for you. Call a professional HVAC technician to diagnose the problem and set things right.

Strange Noises

If your HVAC system is running smoothly, it should be quiet. If you hear strange noises, you should investigate them to find the source of the problem.

If your HVAC system has been in place for some time, you probably know which noises are normal and which ones are new. Abnormal sounds like rattling, clanging, banging, thumping and screeching should always be cause for concern, and a reason to call an HVAC technician for professional service.

Excessive Dryness or Humidity

Your HVAC system is designed to keep your home comfortable, but it also helps control indoor humidity levels. A sudden spike in humidity or excessive dryness should always be cause for concern, so pay careful attention to the early warning signs.

You may think that it is normal for your indoor air to dry out in winter, but excessive dryness could mean your HVAC system is not functioning the way it should. Air that is too dry could mean that excessive moisture is trapped in the HVAC system, and that could lead to the growth of dangerous mold and mildew.

You should never ignore the warning signs of a failing HVAC system. If you spot any of the issues listed above, your next call should be to an HVAC professional. If you catch the problem early, it could be simple and easy to fix. If you wait too long, you could be looking at a big repair bill and significant issues with the comfort of your home.