How can I check myself whether the unit cools as it should? Is there a simple test?
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Otopeni, house, 12,000 BTU Toshiba in the living room, 4 years old. It feels like it cools slower this summer than last year, but maybe that is just an impression because it has been hotter. I have a kitchen thermometer. Can I check anything myself before calling someone?
What is really happening
The temperature split ('delta T') is the simplest indicator of a split unit's condition. It drops when air no longer passes freely through the evaporator (clogged filters, fins covered in biofilm) or when the outdoor unit can no longer reject heat (condenser full of dust). Evaporator fouling studies show airflow drops 5–7% and fan power rises as it clogs, and a dirty filter alone can cost 5–15% of consumption. One extra test: remove the filters and measure again – if the split rises noticeably, the filters were the problem.
- Settings and room conditions.
- Restricted airflow or dirty components.
- A technical issue requiring measurements.
Do not automatically assume low refrigerant.
- A typical evaporator fouls enough to double its pressure drop in about 7.5 years, reducing airflow by 5–7% and raising fan power by 1–10%. [Lawrence Berkeley National Laboratory / , 2002]
- Replacing a dirty, clogged filter with a clean one can lower an air conditioner's energy consumption by 5–15% (US DOE). [US Department of Energy – Energy Saver, 2024]
- Fouling of the outdoor condenser raises pressure drop and condensing pressure, reducing the split unit's capacity and efficiency. [Science and Technology for the Built Env, 2019]
- The evaporator and condenser coils accumulate dirt over time and should be checked every year and cleaned as necessary (US DOE). [US Department of Energy – Energy Saver, 2024]
What we do on site
- We also measure the temperature split on arrival and write it down as a baseline.
- We visually inspect the evaporator and roller with a torch and the outdoor unit in the yard – in Otopeni, near open fields, there is more dust than in the city.
- Sealed double cover, alkaline cleaner, adjustable pressure wash in place, pan and hose flushed, sanitising, filters washed.
- Condenser washed in place at low pressure.
- Interpret the temperature difference together with airflow, humidity, operating mode and the model documentation. One value cannot establish dirt, low refrigerant or incorrect sizing.
What you can do yourself
- The thermometer test, once a month in summer; note the values.
- Wash the filters and repeat the test before calling anyone.
- Look at the outdoor unit: if the fins are grey with dust, you already have your answer.
What NOT to do
- This description suggests a possible cause that needs checking at the unit. Age, price or symptoms alone cannot confirm the fault, contamination or work required.
- Do not measure with the fan on 'Auto' or after 2 minutes – it gives false values.
Prevention
Annual cleaning and a condenser washed before the season keep the delta T at factory values.
When to call us
Interpret the temperature difference together with airflow, humidity, operating mode and the model documentation. One value cannot establish dirt, low refrigerant or incorrect sizing.
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Sources (4)
The information on this page is educational and based on cited sources; it does not replace medical advice. We do not do repairs, installation or refrigerant circuit work.