You don't suspect your air conditioner is in bad shape only when it can't turn on. The smell the unit releases when turned on could indicate it's defective. Different defective AC units release different types of awful odours, and each odour suggests a particular problem. So if you notice a horrible smell in the house when you turn on your air conditioner, don't blame your boots, dirty socks, dust bin or the eggs in the kitchen. The unit you just turned on to freshen your indoor air could be the culprit behind that disgusting stench. Here are some of the awful odours a defective AC unit could release and what they indicate: 

The Unit Smells Like 'Gone Bad' Eggs

Although the modern web or mobile apps help you control your AC unit from anywhere, they might also make you lazy — you no longer inspect the appliance regularly to see if debris, leaves or pests are trapped in it. If dead critters, birds, lizards or rats get trapped in the air conditioner, it will smell like rotten eggs. To avoid such an awful experience again, contact an air conditioning technician to pest-proof the appliance. Although you could be tempted to remove the dead animals trapped in the AC unit yourself, you should let a certified technician do it since you might not access the trapped critters or objects.

The Unit Smells Like the Exhaust of Your Car

AC units don't use a combustion engine to run, so you should be worried when the unit releases an odour similar to what your auto exhaust releases when running. Nevertheless, most AC units use fluids that might release exhaust fume odours when heated. Such smells indicate the unit's refrigerant line is leaking, and it could develop more problems if you don't contact an air conditioning expert in good time. Moreover, when the unit's refrigerant is leaking, more hazardous chemicals could circulate in the house and compromise your comfort and health in a big way. Open the windows to enhance ventilation as you wait for a competent air conditioning specialist to come and fix the issue.

The Unit Smells Mildewy or Mouldy

If water accumulates in the unit's drip lines or other components, it will release a musty or dingy odour. For homeowners with ducted AC units, water in the ducts could also cause this unpleasant odour. If you haven't cleaned the filters for a while now, they might be dirty, causing the mildewy odour. Also, if you turned on your AC unit several months ago, a lot of moisture might have accumulated in the filters, and this could also cause the musty smell. But if you call in an AC technician to inspect the unit and clean its ducts, filters and lines regularly, the mouldy smell will hardly find its way into your home.

No matter what might have caused the awful smell from the AC unit, you should never try to fix it yourself. You might get an electric shock or even leave the unit worse than it was. Always let a professional in air conditioning maintenance diagnose the cause of the appalling odour and fix it no matter how minor it might be.