Written by Industrial Stores Staff 06/26/22
When you get home, you’re glad to have escaped the scorching and stuffy outdoor summer heat. Time for some cool air, at last.
You turn on the AC, sprawl on the couch, close your eyes, and silently thank its inventor.
But there’s an unpleasant smell permeating the room, and you can only trace it to your air conditioner.
What exactly is wrong?
Any of the following conditions can cause your air conditioner to smell bad:
Clogged condensate line
Undrained condensate pan
Dirty air filter
Today, we’ll explore the best solutions and figure out how often your AC needs routine maintenance to remain efficient.
1 - Clogged Condensate Drain Line
An air conditioner works by cooling hot, humid air before fanning it into your home. This cycle causes condensation on the evaporator coil. The condensate drain line channels the resulting water out of the air handler and into the drainage system.
However, constant passage and accumulation of water through the drain line can create favorable conditions for the growth of bacteria, algae, fungi, mildew, and tiny plants. The concentration of this matter culminates in an unpleasant odor.
You can unblock a clogged AC drain line by flushing it with any of these liquids:
Vinegar
Hot soapy water
Peroxide
Expert Tip: Distilled white vinegar is the most effective due to its higher acidity.
Clean the Condensate Drain Line With Vinegar
Step 1. Switch off the AC
Turn the AC off at the thermostat and disconnect the power supply at the circuit breaker.
Step 2. Locate the Condensate Drain Line
Near your AC’s outdoor unit, find a PVC pipe emerging from the AC’s indoor unit, usually mounted on the house wall. Locate a T-shaped vent tee attached to the top of the drain pipe. Remove the cover and examine the blockage.
Step 3. Flush With Vinegar
Add ¼ cup of distilled white vinegar to the blockage. Let it sit still for 30 minutes.
Step 4. Rinse With Water
With a beaker, pour clean water into the pipe, and ensure it allows free flow.
A clogged drain line will leave the drain pan with stagnant water. This will result in a dingy and musty smell.
2 - Undrained Condensate Drain Pan
The air conditioner cools your home by drawing air through its ducts and blowing it over its evaporator coils, which are filled with near-freezing compressed refrigerant.
The mingling of warm and cold air creates droplets on the evaporator coils.
Also known as the AC drip pan, the condensate drain pan collects the water created by the air conditioner’s cooling process by trapping condensate droplets from the evaporator coils.
The condensate drain line empties the drain pan to prevent overflowing and stagnation.
How to Fix a Smelly Condensate Drain Pan
There are typically two different drain pans in an AC unit: the primary and the auxiliary.
The primary pan is permanent and is situated under the evaporator coil inside the handler. The auxiliary drain pan is located beneath the air handler and is removable.
When the condensate stops flowing from the pans through the drain line, the pans will overflow and cause dampness. This will result in an unpleasant musty smell.
You need to have a flashlight on hand to have a clear view of the drain pans.
Step 1. Run the Air Conditioner for About 30 Minutes
This is long enough for your AC to cause flooding on the pans if the drainage system is faulty.
Step 2. Look for Pools of Water and Debris
Look around your AC’s housing and inside the indoor air handler for pools of water. Any water collection is confirmation of a backup.
Step 3. Turn Off the Air Conditioner
Turn off the AC at its thermostat and disconnect the electricity supply to the entire air conditioning system.
Step 4. Remove the Access Panel
Some AC covers have screws, while others are held in place with hooks. If there are screws, remove them with a screwdriver.
To prevent hooks from breaking, release them while pushing the cover inwards with one hand. When you have loosened them all, pull the cover away from the unit.
Pull or turn the control knobs with your fingers. Next, simultaneously push the front cover upwards and gently pull it away. Finally, unhook it at its top and pull it completely off the air conditioner.
Step 5. Inspect the Drain Pan
With a flashlight, check your drain pan for flooding or algal growth. Look out for holes and cracks as well. They can cause leakage and bacterial infestation.
Step 6. Clean and Seal the Drain Pans
Clean both pans with a soft towel and soapy water. If the cracks are not large, seal them with waterproof sealant. But if they are serious, request a quote for a high-quality pan replacement or call an HVAC professional for advice.
3 - Dirty Air Filter
If your AC’s air filter remains unreplaced or unserviced frequently, it will end up with deposits of:
Dust
Insects
Pet hair
Bacteria
Dust mites
Pet dander
Even without humidity, this combination is likely to produce a stench hazardous to your health.
That’s why you need to regularly clean or replace your AC filter with a high-efficiency brand.
How to Replace Your AC Filter
If you’re not sure about the location of your filter or how to access it, ask your HVAC technician to show you. Alternatively, you can read the AC manufacturer’s technical manual.
Expert Tip: Always wear gloves and a mask when handling an AC air filter to protect yourself from contamination and inhaling toxic substances from the filter.
Step 1. Turn Off the Power
Turn the AC off at the thermostat and at the main switch.
Step 2. Remove the Old Filter
Slide or pull the filter out of its slot.
Step 3. Check the Filter’s Condition
After getting it out, check if it's clogged. Is it covered with a murky veneer? If you hold it to the light, is it allowing any of it to come through? If not, it’s time to clean or replace it.
Expert Tip: In places with high humidity or smog, you’ll need to clean or replace your AC filter more frequently.
Step 4. Clean a Reusable Filter
If your air filter has a MERV rating of 1 to 4, it’s reusable. Some reusable filters can be cleaned by washing while others by vacuuming. Check the user’s guide for precise instructions on how to clean it.
Step 5. Insert the Cleaned or New Filter
Insert the filter in its slot, aware of the arrow indicating the airflow direction. Ensure the arrow points away from the return air duct but toward the air handler.
This table will help you see the differences between disposable and reusable air filters.
How To Prevent Bad Smells From Your AC
Maintain your AC’s efficiency by cleaning the drain line, pan, and air filter every month.
If your AC seems to miss the efficiency mark even after taking the above steps, call an HVAC professional to appraise it.
Expert Tip: Always turn off the AC and the main electricity supply to protect yourself and your AC.
Enjoy Quality HVAC Service Always
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Frequently Asked Questions
How can I know if my AC's filter is washable?
Washable filters are usually identified by their metal frame and have a maximum MERV rating of 4. Unlike disposable filters, they allow tinier substances such as smoke and pet dander to pass through, reducing their effectiveness.
Why is my AC smelling like car exhaust?
Exhaust fume smell from an AC may signify a leak of fluids such as refrigerant. To avoid toxicity, turn off your AC at once and contact your local HVAC for a professional assessment.
Where can I check if my AC smells like rotten eggs?
The smell of rotten eggs is mostly a sign of a natural gas leak in your home. And if it becomes more perceptible when you turn on your AC, then the gas is making its way into your air conditioning system.
Turn off your gas supply at once, vacate the building and call the fire department.
A dead pest in your AC’s ductwork or attic is also a likely reason. If you spot a dead animal along your ventilation system, call pest control to help with safe disposal.
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