Air conditioning servicing: what a proper visit covers

What actually degrades

Filters

They capture dust before it reaches the evaporator coil. As they load, airflow drops. Reduced airflow over a cooling coil makes the coil colder, which can ice it up, which reduces airflow further – a feedback loop ending in a unit that blows almost nothing and then trips. Filters are the single biggest determinant of performance and they are user-cleanable on almost every unit.

The indoor coil

What gets past the filters lands on the coil fins, along with condensation. Dust plus permanent moisture becomes a damp mat that restricts airflow and provides a biological growth site – which is where the musty smell comes from. It needs proper cleaning with a suitable coil cleaner, not a wipe.

The condensate tray and drain

The same growth blocks drain lines. When the drain blocks, the tray overflows – down a wall from a wall unit, or into the ceiling from a ducted or cassette unit. It is the most common cause of visible damage from air conditioning and it is entirely preventable.

The outdoor coil

Leaves, grass cuttings, pollen and general debris clog the fins. A blocked condenser cannot reject heat, so pressures rise, efficiency falls and the compressor runs hotter. In a Norfolk garden in autumn this happens quickly.

Refrigerant charge

A sealed system should not lose refrigerant. If it is low, there is a leak – and topping up without repairing it is both wasteful and not permitted.

What a service should include

1. Filters removed, cleaned or replaced.
2. Indoor coil inspected and cleaned properly with a suitable coil cleaner.
3. Condensate tray cleaned, and the drain line cleared and flow-tested, not just looked at.
4. Condensate pump checked, cleaned and tested where one is fitted.
5. Outdoor coil cleaned and the clearances around the unit checked.
6. Fan motors and blades inspected – an unbalanced outdoor fan is a common noise complaint.
7. Operating pressures and temperatures measured, with superheat and subcooling assessed to confirm the charge.
8. Electrical connections checked for tightness and signs of heat.
9. Controls and both modes tested, including the heating changeover.
10. Refrigerant type and charge confirmed and recorded.
11. Findings recorded in writing.

Note that a service visit is not the same as an F-Gas leak check. Where a system’s CO2e requires statutory leak checking, that is a separate obligation with its own frequency and its own records – see F-Gas compliance.

Refrigerant and the law

Two things follow for any owner, domestic or commercial:

• Only a qualified person may handle refrigerant, and the business employing them must hold company certification. Both are required – employing qualified engineers is not sufficient on its own. This applies to domestic splits as well as commercial plant.
• Topping up a leaking system without repairing the leak is not permitted, and deliberate release is an offence.

Domestic splits are usually below the charge threshold that triggers mandatory periodic leak checking, but the handling and certification requirements apply regardless of size. It is a fair question to ask any contractor.

What you can do yourself

1. Clean the filters monthly in heavy useLift the front panel of the indoor unit, slide out the filters, rinse in warm water, and let them dry completely before refitting. Never refit a damp filter.
2. Keep the outdoor unit clearNo leaves piled against it, no shrub growing across it, nothing stacked in front. Clear airflow on every face.
3. Brush the outdoor fins gentlyWith a soft brush, in the direction of the fins. Do not use a pressure washer – it bends the fins and drives debris in.
4. Run it briefly in winterTen minutes of cooling once a month through the off season keeps the compressor oil circulating and the seals from drying, and confirms it still works.
5. Use the self-dry functionMany units have one. It runs the fan after cooling stops to dry the coil, which substantially reduces the musty smell problem.
6. Watch for waterAny dripping from an indoor unit is a drainage problem and should be dealt with before it stains a ceiling.
7. ListenNew rattles, buzzes or changes in pitch from the outdoor unit are worth reporting rather than getting used to.

Frequency

Coastal exposure deserves a note in this county. Salt-laden air corrodes aluminium fins and steel casings, and units within a few miles of the coast visibly age faster. More frequent cleaning of the outdoor coil genuinely extends their life.