When an air conditioner's electricity bill goes up, the first thoughts are that the unit is getting old or the weather has gotten hotter. Yet the cause we encounter most often in the field is much simpler: the unit has not been maintained for a long time. Dust, dirt and small refrigerant leaks build up over time, and the air conditioner has to run longer and harder to deliver the same cooling.
In this article we explain the ways in which lack of maintenance increases energy consumption, the range the increase usually falls in, and what you can check yourself.
Why does a poorly maintained air conditioner use more electricity?
A poorly maintained air conditioner uses more electricity because it does a worse job of taking heat from the indoor space and rejecting it outside. An air conditioner is a heat mover; air must pass easily through the coils and the refrigerant must be at the right amount. When one of these balances is off, the compressor runs at higher pressure and for longer.
The compressor is the part that consumes most of an air conditioner's electricity. So anything that strains it shows up directly on the bill. The problem is not one big failure but small losses that add up.
How much does a dirty filter increase consumption?
A dirty filter increases consumption by reducing the amount of air passing through the indoor unit, and the US Department of Energy (DOE) states that replacing a dirty filter with a clean one can cut consumption by 5 to 15 percent. When airflow drops, the indoor coil cannot absorb enough heat, the room cools slowly and the unit runs longer.
When the filter is badly clogged, the indoor coil can get too cold and ice up. An iced coil lets almost no air through; the unit runs but the room does not cool. At this point the increase in consumption is no longer a measurable loss but wasted energy.
Cleaning the filter is a job a home user can safely do. Turn the unit off and unplug it, open the front panel, remove the filter, wash it with lukewarm water and put it back once it is completely dry. With heavy use, doing this every 2-4 weeks is enough.
How much loss do a dusty coil and condenser cause?
A dusty condenser raises the condensing temperature, causing the compressor to draw more power. As a general rule, every 1 °C increase in condensing temperature raises compressor consumption by about 2-3 percent; the rate varies by unit and conditions.
When the outdoor unit's coil is covered with leaves, pollen, soot and dust, it cannot reject heat. If the fouling is severe, the condensing temperature rises by a few degrees; this alone can mean an increase of more than 10 percent. This fouling happens very quickly on outdoor units placed on rooftops, by roadsides or near construction.
The indoor coil, on the other hand, gets matted over time with fine dust that gets past the filter. This layer cannot be removed as easily as the filter; it requires a chemical wash or cleaning with a suitable chemical. A dirty indoor coil is also a source of bad odor and mold.
How does low refrigerant affect energy consumption?
Low refrigerant reduces the air conditioner's capacity, so the unit has to run much longer to deliver the same cooling. As the amount of refrigerant drops, not enough gets to the evaporator, superheat rises and the compressor is not cooled adequately.
A small leak can go unnoticed for months. The user just says "the air conditioner doesn't cool like it used to" and sets the thermostat lower. This both increases consumption and shortens the compressor's life.
Low refrigerant can only be diagnosed correctly with a manifold pressure measurement and superheat calculation. Working on the refrigerant circuit, searching for leaks and charging is a job only for a licensed, certified technician. The leak must be found and fixed before refrigerant is added; otherwise the added refrigerant is lost again within a few months.
How big can the total loss be?
The total extra consumption of a poorly maintained air conditioner is usually between 10 and 30 percent; if several problems occur together, this rate can rise even higher. The exact value depends on the type and age of the unit, hours of use and the degree of fouling.
Is your air conditioner using too much?
With a measured maintenance visit, let us check pressure, current and coil condition, and report the cause of the efficiency loss in writing.
| Problem | Effect | Who fixes it? |
|---|---|---|
| Dirty filter | Airflow drops, run time increases | User |
| Dusty indoor coil | Heat transfer decreases, odor develops | Technician |
| Dirty outdoor unit coil | Condensing pressure and compressor current increase | Technician |
| Low refrigerant | Capacity drops, compressor overheats | Certified technician |
| Loose electrical connection | Heating, voltage drop, failure risk | Certified technician |
In commercial buildings, these percentages turn into larger sums. In a VRF system with dozens of indoor units or in a chiller, even a few points of efficiency loss make up a noticeable item in the annual budget.
What signs show an efficiency loss?
An air conditioner suffering an efficiency loss usually runs longer, cools the room slowly and becomes noisier than before. These signs alone do not mean a breakdown, but they show that it is time for maintenance.
The most common signs are air from the indoor unit that is not as cold as it used to be, an outdoor unit that almost never stops running, a bill for the same month that is noticeably higher than in previous years, and a heavy odor from the indoor unit. Frost or oily stains on the pipe connections at the outdoor unit point to a refrigerant leak.
When you notice these signs, check the filter first. If the filter is clean and the problem continues, request maintenance instead of running the unit continuously; a compressor that is working under strain both wastes energy and gets closer to failure.
What should you do to save energy?
The way to prevent loss caused by lack of maintenance is regular, measured maintenance. What the user does and what the technician does complement each other.
- What you can do yourself: Clean the filter regularly, keep the area in front of and around the outdoor unit clear, use the thermostat at around 24-26 °C, and keep doors and windows closed.
- What the technician needs to do: Indoor and outdoor coil cleaning, pressure and superheat measurement, leak check, compressor current measurement and a check of electrical connections.
We explained how often maintenance should be done in our article why and how often air conditioner maintenance should be done. If you are curious about the effect of filter type on consumption in fan coils and air handling units, you can also look at our article nanofiber filters and fan coil energy consumption.
At YOİ Mühendislik, during our periodic maintenance visits we measure and record pressure, current and temperature values on every unit. This way efficiency loss is spotted before it shows up on the bill.
Frequently asked questions
Does air conditioner maintenance really lower the electricity bill?
Yes. In a unit with a dirty filter, dusty coil or low refrigerant, consumption usually drops noticeably after maintenance; how much depends on the unit's previous condition.
Is it enough if I clean the filter myself?
Filter cleaning covers an important part, but matted dust on the indoor coil, outdoor unit dirt and low refrigerant can only be fixed by technician maintenance. Both need to be done together.
How can I tell if my air conditioner is low on refrigerant?
Cooling more slowly than before, and frost or oil traces on the pipe connections at the outdoor unit, are typical signs. For a definite diagnosis a technician needs to measure the pressure; do not interfere with the refrigerant circuit yourself.
What other problems does a poorly maintained air conditioner cause?
Besides energy loss, the risk of bad odors, water dripping, icing, noise and compressor failure increases. In the long run, repair costs can exceed maintenance costs many times over.