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Heating & Air Conditioner Odors

Posted on AC Repair, AC Tips, The Cooler Blog, Tips October 17, 2013

Believe it or not, odors in the heating and cooling systems are very common. There are many different types of odors and causes, but there are five general categories. Odor problems can be as serious as a gas leak or as simple as a dirty air filter. Unusual odors can indicate a serious problem and should never be ignored.

  1. Electrical Odor – usually caused by parts overheating like indoor blower motors. With mechanical failure, the motor overheats and the wire insulation and motor windings start to melt, causing the odor. Sometimes loose electrical connections cause wires or plastic relays to overheat. A very dirty air filter can cause the odor. If the airflow is restricted enough, it could cause electric resistance heaters to overheat and burn-out. Check your air filter. If it is not blocked, shut the equipment off at the breaker (if possible), and call for service.
  2. Burning Odor – similar but worse than an electrical odor. Sometimes it’s accompanied by smoke, caused by parts or wiring burning-up. Debris such as plastic that got caught in the ductwork can lead to melting on the electric resistance heaters or heat exchanger. Check your air filter. If it is not blocked, shut the equipment off at the breaker (if possible), and call for service.
  3. Gas Odor – If you smell gas and suspect a gas leak, then open the windows, leave the house immediately, and call the gas company. If you smell an odor that resembles gas coming out of the supply vents, it usually is burning dust that settled on the heat exchanger during the summer months. If the odor isn’t coming from the vents, try to pinpoint where the smell is coming from. If it is gas, it usually would be from a leak in a pipe fitting or at the equipment itself. Gas explosions are very rare and carbon-monoxide for the most part is odorless. If you can’t locate the source of the odor, call the gas company.
  4. Oil Odor – usually caused by one of two things; an oil leak/drip or an oil burner that is not working properly. Check the burner itself, the oil tank, filter and oil line. If there are no signs of an oil leak then it is most likely a burner problem. If you notice rumbling, banging sounds, or an oil odor while the burner is running, call for service immediately. One other common problem today is that new houses are insulated so well and are built so tight that they run out of combustion air, causing odor problems.
  5. Damp & Musty Odor – almost never due to a problem with your equipment. It’s usually related to an outside water source getting into the house. Check for air leaks in the return ducts. Check for water damage to the ducts or air handler itself. You should consider having your ducts cleaned. Run a dehumidifier and see if the odor goes away.


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