What happens during an air conditioning service?

Before the visit

A smooth service starts with a few details. When you book, have these ready:

• the make and model, usually on a label on the side of the indoor unit or the outdoor unit
• how many indoor units there are, and what types (wall, ceiling cassette, ducted)
• where the outdoor unit is and how to reach it
• any symptoms: smells, drips, weak cooling, error codes

In Camden, outdoor units are often on the flat roof of a rear extension, in a lightwell below a converted house, or on a shared roof over a mansion block in West Hampstead. If access is through a neighbour’s flat, a locked roof hatch or a managing agent, sort that before the day. Our Camden area page explains why units end up in these spots.

Step by step

Step	What the engineer does	Why it matters
1. Check operation	runs the unit, notes any fault codes and sounds	gives a baseline before cleaning
2. Protect the room	dust sheets, drip sheet or bag under the unit	coil cleaning is wet
3. Filters	removes, cleans or replaces them	clogged filters cut airflow and cooling
4. Indoor coil and fan	cleans the coil and the barrel fan with suitable cleaner	dirt here causes smells and weak cooling
5. Drain tray and pipe	clears the tray and flushes the drain, tests any pump	blocked drains cause leaks
6. Outdoor unit	clears debris, cleans the coil, checks fixings and mounts	airflow outside affects efficiency
7. Electrics	checks connections, isolator and controls	loose connections cause faults
8. Performance	measures air temperatures and refrigerant pressures	spots low refrigerant or other faults
9. Heating mode	runs the system in heat mode if reversible	checks the reversing valve and defrost
10. Record	notes work done and anything found	warranty and future reference

What a good service is not

A good service is not just a filter rinse and a squirt of spray. It is also not a routine regas. Home split systems are sealed circuits. If the engineer finds the refrigerant is low, that points to a leak, and the right next step is to find and repair it before recharging. Our guide to home air conditioning regassing explains why.

Anything that involves the refrigerant circuit must be carried out by an engineer with an F-gas qualification, working for a company certified by an approved body. The gov.uk list names Refcom, the F-Gas Register (Quidos) and Bureau Veritas. You can ask for the company certificate number before the visit.

Ducted and cassette units

Ducted units hide in a ceiling void, so the engineer works through an access hatch. If the hatch is small, painted shut or above a wardrobe, the visit takes longer. Ceiling cassettes have a grille that drops down for filter and coil access, and most have a built in condensate pump that should be tested. If your system is ducted, see our ducted air conditioning guide for why access matters.

What you get at the end

You should get a short written record, by email or on paper, listing:

• the units serviced
• work done, such as filters cleaned, coil cleaned, drain flushed
• readings or observations, such as pressures and temperatures within the expected range
• anything that needs attention, with a clear explanation
• a suggested date for the next service

Keep it with the installation paperwork. Manufacturers often ask for proof of yearly servicing when you make a warranty claim, and a buyer or tenant may ask for it when you sell or let a flat.

Getting the timing right

For most London homes, one service a year in spring makes sense, before the first hot spell. Systems used for winter heating as well can benefit from a check in autumn too. Our guide to how often to service air conditioning covers frequencies for homes and offices, and our servicing page explains how to book.

Questions worth asking

At the end of the visit, it is reasonable to ask:

• were the refrigerant readings normal?
• is the drain falling properly, or is a pump doing the work?
• is the outdoor unit position causing any problems, such as leaves, sun or poor airflow?
• is there anything likely to fail soon?

Problems a service often finds

On London homes, the most common findings at a yearly service are:

• matted filters that have not been rinsed since last summer
• slime in the drain tray that is close to blocking the outlet
• a noisy or failing condensate pump, often in units on inside walls
• leaves and grime packed into the outdoor coil, especially on flat roofs and in lightwells
• loose wall brackets or perished anti vibration mounts
• slightly low refrigerant, pointing to a slow leak at a joint

Most of these are dealt with on the day. A refrigerant leak needs a separate repair visit, because the leak must be found and fixed before the system is recharged.