Air conditioning has quietly stopped being unusual in British homes. Heat pumps brought reversible systems into ordinary houses, a run of hot summers did the rest, and a lot of people now own a piece of equipment they have never had serviced because nobody told them it needed it.
Then it stops cooling properly, somebody rings a number, and a price appears with no explanation attached. This is a short guide to what the work actually consists of, so you can tell the difference between a service and an invoice.
The difference between a clean and a service
Most of what gets sold as an air conditioning service is a clean. That is not an insult — cleaning is genuinely most of the job — but the two are not the same, and the gap between them is where people overpay.
A clean means the filters come out and get washed, the indoor unit is wiped down, and the outdoor unit gets a rinse. It takes twenty minutes. It is worth doing and you can do most of it yourself.
A service means somebody puts gauges on the system. They check the refrigerant pressures against what the unit should be running at, measure the temperature difference between the air going in and the air coming out, chemically wash both coils rather than rinsing them, clear the condensate drain line, and check the electrical connections for heat damage.
The second one tells you whether the system is working. The first one tells you it looks clean. If a quote does not mention pressures or a temperature differential anywhere, you are buying the first one.
Why coils matter more than filters
Filters are the part everyone knows about, because they are the part you can see.
Coils are the part that decides whether the system works. The indoor coil is where heat is pulled out of the room air; the outdoor coil is where that heat is dumped. Both are dense arrays of thin aluminium fins, and both load up with a fine layer of dust, grease and — outdoors — whatever the weather brings.
A coil with a visible film on it is already costing you. The system compensates by running longer to hit the same temperature, which you pay for on the electricity bill long before you notice the room is not as cold as it used to be. This is the single most common reason a system “stops working well” with no fault code and nothing obviously broken.
A proper coil clean is a foam chemical wash, left to lift the deposits, rinsed through, with bent fins combed straight afterwards. A hose on the outdoor unit is not the same thing.
The refrigerant conversation
Here is the one piece of knowledge that will save you the most money.
Refrigerant is not consumed. It circulates in a sealed loop. A system that is low on gas has a leak, and a system with a leak will be low again.
So any quote that offers to “top up the gas” without first finding the leak is selling you the same job twice. The correct sequence is: pressure test to locate the leak, repair it, pull the system into vacuum to remove air and moisture, then weigh the new charge in on scales. Weighed, not guessed — overcharging a system is as damaging as undercharging it and is a genuinely common cause of compressor failure.
If somebody connects a bottle, watches a gauge, and disconnects, you will be calling them again.
Reading a quote
A few things separate a real quote from a number plucked from the air.
It names the parts. “Repair” is not a line item. “Replace capacitor” is.
It says whether diagnosis is charged separately, and whether it comes off the bill if you go ahead.
It carries a warranty on the work, with a stated length. Ninety days is a normal floor for a repair.
It does not change at the end. A quote that becomes a different number when the invoice arrives was never a quote.
And one counter-intuitive flag: be suspicious of the cheapest number. A call-out priced below what the labour alone costs is a door-opener, and the margin has to reappear somewhere — usually as an unnecessary gas top-up, or a part replaced that did not need replacing.
Nobody publishes prices, and that is the problem
Ask three companies what a coil clean costs and you will get three versions of “it depends.” It genuinely does depend — on the size of the unit, how accessible it is, what parts are involved — but the ranges are entirely knowable, and a company that works on these systems every day knows exactly what they are.
It is worth seeing what transparent pricing looks like, because once you have, opaque pricing stops feeling normal. In Dubai, where cooling runs most of the year and the servicing market is correspondingly mature, some operators publish their full price list openly rather than quoting blind — a split-unit service at AED 120 to 250, a chemical coil clean at AED 150 to 300, a typical repair at AED 200 to 800, each with what the number includes written next to it. You can read the whole thing: here is a worked example of AC service costs in Dubai published as a plain price list rather than a quote request.
The figures are not transferable to the UK — different labour rates, different market, different climate load. The format is. A company willing to print its ranges and explain what moves a job within them is telling you something about how it will behave when it is standing in your hallway.
A sensible maintenance rhythm
For a domestic system in the UK:
Wash the filters every couple of months through the months you use it. Takes five minutes, needs no tools, and prevents most of the gradual decline people put up with.
Keep the outdoor unit clear. Half a metre of space on the intake side, nothing leaning against it, no shrub growing into it.
Get a proper service once a year, ideally in spring before you need it rather than in July when every engineer is booked.
Call somebody when the behaviour changes — longer run times, a smell when it starts, water where water should not be, or a noise that is new. Changes in behaviour are cheap to investigate and expensive to ignore.
The short version
An air conditioning service is a measurement job, not a cleaning job. If nobody puts gauges on your system and nobody tells you the numbers they found, you have paid for a wipe-down.
Ask what the quote includes and ask whether the price can move. Ask what happens if it fails next month. The answers will tell you most of what you need to know before anyone touches the equipment.