4 Signs Your Central Air Needs Service

Four signs your central air needs service - Appolo Heating

Turning on your central air only to be greeted by a metallic clicking noise or a sudden smell that reminds you of soggy socks that got lost behind the hamper for a couple weeks? What about waking up in the middle of the night only to find that your unit has totally stopped cooling the air and is just blowing ninety degree humid air back in your face? Chances are, if you have air conditioning, you’ve run into a minor problem (or maybe a major one) that was irritating enough to have you calling your HVAC tech to see what gives. So we’ve come up with the four most common signs your AC needs servicing to help avoid having to play the guessing game.

Low Pressure Air/No Air Blowing Out at All

Your AC system should be pumping out a significant amount of air, enough to flow through and cool the whole room. However, if your AC is barely emitting cool air, or isn’t circulating any at all, you’ve got an issue. The most common cause of decreased pressure is a clogged air filter. Your unit can only blow out as much air as it’s taking in and, when you have a dirty air filter or cleaner that can greatly reduce the amount of air it can take in before cycling through and blowing out.

An easy fix would be to make sure you’re changing your air filter on a regular basis. Standard 1” fiberglass filters should be changed every month, while the higher efficient media type air cleaners that are available should be changed every 3 to 12 months dependent upon the manufacturer’s recommendations. Frozen evaporator coils are another issue that could be caused by a clogged filter, a blocked return vent, or a refrigerant leak. Essentially, the coils work by cooling the air that passes over them on the way into your home. However, if they freeze over, the ice will block air from being able to enter and could potentially cause a leak when it finally thaws out (You’ll want to call an HVAC technician for this one). Leaky or blocked air ducts caused by holes or kinks in your ductwork could impact your air flow as well. So if you’ve had recent work or construction done in your home, followed by reduced airflow, that could be your culprit.

Weird Noises

Weird noises coming from your AC system can be alarming, but they’re usually not dangerous. It could just mean you need a new belt, or a stick fell into the fan.

If your AC system sounds like it’s screaming at you (a high pitched, shrill, hissing sound) it could be due to your compressor having too much pressure built up in the system. This can be caused by a number of things and will require servicing.

A knocking or clunking noise is usually caused by something stuck in the unit that the fan is hitting. You won’t want to leave the system running, as it could create damage to the fan. If you are unable to remove whatever is in there, have it serviced before tuning it back on.

In older systems, squealing noises are usually caused by the fan belt on your blower motor being either misaligned or worn out. If you think it might be a metallic screeching noise, that could be due to the bearings in your blower motor or fan wearing out. You’ll want to have those repaired or replaced by a technician sooner rather than later.

Whenever any of the above noises occur, we recommend turning the system off until you can have it serviced, otherwise continuing to allow it to run could be cause for a more expensive repair.

Strange Smells

The air coming into your home should smell fresh, clean, and not much like anything else. If you notice your vents are emitting any weird or foul smells, something is up. This could be caused by something as simple as having a dirty air filter or cleaner, or it could be caused by your ductwork being dirty due to years of dust and dirt buildup that your air filter or cleaner did not prevent. The filter itself should be an easy fix, while cleaning the ductwork will require a professional with the right equipment to do it properly.

If it is a musty or moldy smell, this is not common and could be due to moisture build up that has built up in your ductwork during the non-cooling season if they are installed in an unconditioned space (crawl space or attic), which could have caused mold or bacteria growth. You’ll want to have a professional check it out to make sure there hasn’t been any major water damage and to properly get rid of any mold or bacteria growth that is there. This will require the ductwork to either be cleaned or replaced dependent upon its location and condition.

A burning/overheating smell is most likely indicative of one of the mechanical parts (the blower motor or compressor) overheating, and/or one of the electrical wires getting too hot and beginning to burn. These kinds of smells are usually due to an electrical problem, so you’ll want to make sure the electricity is turned off, and call a professional AC repair technician to look it over.

Although this is unrelated to your AC system, if you notice a sulfurous smell (like rotten eggs), it could indicate a natural gas leak. Most natural gasses are odorless by themselves, but utility providers have been known to add in the smell to alert inhabitants of a possible leak. In this case, it would be best to open your windows, get out of the house for extra precaution, and to immediately call your utility company to take a look.


The air coming from your air conditioning unit should be dry… and so should the area around it. If you notice any leaking or water build up, that’s a sign there’s an issue. Especially if the water is coming from the AC itself, which could signal that refrigerant is also leaking out of the unit (and refrigerant can be dangerous to pets and unknowing family members).

The leak could possibly be just water, which would be cause by a clogged drain tube (the most common cause of leaks in AC units). If you have an older unit, the evaporator coil drain pan may be damaged or rusty and in need of a replacement. By themselves this isn’t dangerous, but they could cause bigger issues with your unit if it isn’t taken care of sooner rather than later.

A dirty air filter / air cleaner or a low level of refrigerant could also be the culprit of a leak, as either of those could cause the evaporator coil to freeze over, making the melting ice responsible for the leak. Low refrigerant levels could also cause the coil to freeze over, and the melted ice could overflow your drain pan.

Chances are, if it’s leaking, something is wrong, and you should have your unit serviced ASAP.

No matter what abnormalities may arise with your central air over the year, it’s important to get it serviced and cleaned by a professional yearly to catch any problems early on. This will keep your system running in A+ condition so when it comes down to one of those boiling hot days in the summer, you’re good to go.

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