A system that’s sat unused, or only used for heating, through the winter can develop small problems that only show when it’s asked to cool hard. Spring, before the first warm spell, is the time to check. It leaves room to book a service or repair before engineers get busy in a heatwave.
None of these checks involve opening the casing or touching the refrigerant side. If in doubt, leave it to an engineer.
Check 1: clean the filters
With the system switched off, lift the front panel of the indoor unit (it usually hinges up) and slide out the filters. Hold them up to the light. If they look grey or fluffy, rinse them gently under lukewarm water or vacuum them, let them dry completely away from direct heat, and refit. The manufacturer’s user manual shows the exact steps for your model.
Clean filters are the simplest thing you can do for performance. Blocked ones restrict airflow, cut cooling and can make the indoor coil ice up. Our step by step guide to cleaning filters has more detail.
Check 2: test run in cooling mode
Switch on in cooling mode and set a temperature a few degrees below the room temperature. Give it some minutes to settle, then check:
- the air from the indoor unit feels noticeably cool;
- the outdoor unit’s fan is turning and you can hear the compressor running;
- there’s no error code or flashing light on the indoor unit;
- there are no new rattles, grinding or squeals from either unit;
- there’s no musty smell that doesn’t clear after a few minutes.
If the air isn’t cool, the outdoor unit doesn’t start, or an error code appears, note it down and call us. Our guide to air conditioning not cooling explains common causes.
Check 3: clear around the outdoor unit
Winter leaves, plant growth, a new shed or garden furniture can all crowd the outdoor unit. It needs open space around it to move air; the manufacturer’s installation manual sets out the minimum clearances. Clear away leaves and debris (with the power off at the isolator), cut back plants, and make sure nothing is stored against the front grille.
Look at the fins on the coil. If they’re clogged with dirt or flattened in places, mention it when you book a service: an engineer can clean the coil and straighten fins properly. Don’t use a pressure washer, which can flatten fins and force water where it shouldn’t go.
Want it done properly? AirCon Doctor installs, repairs and services air conditioning and heat pumps across London and the South East, from our base in East Grinstead. We’re an F-Gas certified company and NICEIC approved. Get a fixed-price quote.
Check 4: check the condensate drain
After the test run, look at where the condensate pipe comes out, usually on an outside wall or into a drain. Once the system has been cooling for a while, it should be dripping or running a little. Make sure the outlet isn’t blocked by leaves, soil or a plant pot, and isn’t discharging somewhere it causes a problem.
Indoors, watch for any drips from the indoor unit. If you have a condensate pump, it should run quietly from time to time. A pump that’s silent when there should be water, or running all the time, needs a look. Our guide to leaking water covers the causes.
Check 5: book a service if it’s due
If your system hasn’t been serviced in the last year, book one before summer. A service cleans the coils, fan and drain tray, checks the refrigerant circuit’s performance and the electrics, and gives you a record. See what an annual service includes. Our annual service is £95 to £150 + VAT.
For businesses, check whether any system is due a legal F-Gas leak check. Systems with 5 tCO2e or more of refrigerant need one at least every 12 months. It’s easier to fit that in during spring than in July.
Bonus: get the settings right
- Check the timer and clock are correct after any power cuts over winter.
- Replace the remote’s batteries if the display is faint.
- If you have an app, make sure it still connects to the unit.
- Close blinds on sunny windows during the hottest part of the day so the system has less to do.
- Pick a moderate set temperature and leave the system running steadily rather than switching it on and off.
Our heatwave tips cover getting the most from your system when it’s really hot.
Quick answers
When should I get my air conditioning ready for summer?
In spring, before the first warm spell. That leaves time to book a service or repair before engineers get busy.
Can I clean the outdoor unit myself?
You can clear leaves and debris around it with the power off. Coil cleaning and anything inside the casing are best left to an engineer.
My unit blows air but it isn’t cold. What should I do?
Clean the filters and check the outdoor unit is running. If it still isn’t cooling, call an engineer: it could be a refrigerant, sensor or electrical fault.
Related services
More advice
- Air Conditioning Annual Service: What’s Included and Why It Matters
- How to Clean Air Conditioning Filters: Step by Step Guide
- Air Conditioning in a Heatwave: How to Get the Most from Your System
- Air Conditioning Not Cooling: Causes and How to Fix It
- All advice
This guide is general information, checked against the sources linked on 30 October 2026. It isn’t legal, tax or financial advice. Rules, grants and product ranges change, so check the current position before you rely on it.