Air conditioning, serviced so it actually costs less to run.

A £29,000 replacement quote, fixed for under £4,000.

A high-end mixed-use development in East London Docklands had a fault on a Daikin VRV system serving 47 apartments across three blocks — premium towers with a single penthouse on the top floor of each, private lift opening into the flat, full Thames views. The managing agent couldn’t let cooling capacity to those residents drop.

Four contractors had already looked at it. All four offered the same two options: isolate the faulty outdoor unit and lose capacity to the building, or replace the whole rooftop unit — crane hire, scaffolding, weeks of disruption — quoted at £29,000. I was called in fifth, and only heard about the other four at the end of the visit.

The approach was simple. The manager showed me the units and which one tripped the electrics when the fault occurred — that narrowed the suspect immediately. Up to the roof, local isolation, cover off. A thorough look inside found one anomaly: a small black mark on an electronic board. The compressor inverter module is a separate board bolted onto the main PCB; unbolting it revealed a much larger burn across several components underneath, invisible from the front. Fault found.

Resistance and insulation-resistance tests across the compressor windings came back good. It was a two-compressor unit, so I programmed the failed compressor out of the PCB to keep it running on the other one while the part was on order, and sent the quote the same day — with the caveat that full operation could only be confirmed once the new module was fitted, since I couldn’t rule out that the failure had affected the main PCB.

Time on site: under two hours. Repair: just under £4,000 — most of it the inverter module itself — against £29,000 to crane off and replace the whole unit. The four before me weren’t bad engineers; they were parts-replacers without the diagnostic depth for inverter-drive electronics on a large VRV. That gap is real, and diagnosis-led repair on commercial systems is the strongest part of what I do.

The faults I see most — and fix.

Most air conditioning faults fall into a handful of recurring patterns. After years of service and repair work, the list looks like this:

• Refrigerant loss at flared connections — the single most common failure, usually a slow leak that shows as gradual loss of capacity rather than a sudden stop.
• Condenser coil leaks on outdoor units, occasionally indoor coil leaks (rarer — usually a heat-and-cool unit run on heating in conditions it wasn’t suited to).
• Compressor inverter module failures — the Docklands case is the headline, but these recur on VRV/VRF systems.
• Fan inverter module failures — similar pattern, similar diagnosis.
• Outright compressor failure — usually end of life, often after years on a low charge or blocked airflow.
• Defrost faults in heating mode — a unit that won’t defrost ices up and stops heating; often blamed on the compressor when it’s a £40 sensor.
• Controller and communication faults between indoor and outdoor units, especially on VRF/VRV where addressing and bus wiring matter.
• Condensate pump failures on concealed and high-wall units — a stained ceiling is usually the first sign.
• Capacitor degradation on non-inverter compressors in older VRV/VRF — the compressor draws hard on startup, the cables heat, the insulation melts at the terminals, and you trip the electrics or burn the board. I measure them every visit and quote replacement before they fail.
• Grease- and flour-choked filters in commercial kitchens — one Watford pizza shop had all three units’ filters solid with flour; the owner had spent two years blaming the installer, never having been told to clean them.
• Filters and coils blocked by years of neglect — domestic units run a decade unopened: bad smells, lost capacity, and electricity use that creeps up so slowly nobody notices.
• A flat remote-control battery — sounds trivial, isn’t. I check the remote first because it’s a five-minute fix, and I’d rather tell you that than charge a callout.

What’s in your system — a quick refrigerant reference.

For F-Gas record-keeping, and for understanding what your engineer is working on, here’s a plain reference to the refrigerants commonly found in UK systems. Any system on a phased-down refrigerant has a finite life — at some point the gas becomes unavailable or so expensive that replacement is the rational call, and I can advise on that timeline as part of PPM.

• R22 — older AC, now phased out. It can’t be topped up legally; replacement is the only legitimate path.
• R410A — the workhorse through the 2010s, still widely installed and serviceable; a higher-GWP blend now being phased down.
• R32 — common on newer splits and VRF; mildly flammable (A2L), with lower environmental impact.
• R290 (propane) — newest kit; flammable (A3), with strict installation rules.

Older vehicle air conditioning used R134a, now moving to R1234yf. For the refrigerants in commercial fridges, freezers and cold rooms, see my commercial refrigeration page.

Why I check refrigerant charge by weighing it.

There’s a lot of bad practice around refrigerant, and the part most of the trade skips is this: on a modern system you can’t read the charge off the gauges. Today’s units run inverter-driven compressors whose software constantly modulates them to the most efficient operating point, so the unit sits on part load most of the time. Your pressures, sub-cooling and superheat are telling you the part-load story at that moment — not what mass of refrigerant is actually sealed in the system.

For most fault-finding, inspecting accessible joints for oil staining plus electronic leak detection finds the problem, and that’s standard service work. But where pipework is concealed or at high level and a unit is underperforming for no visible reason, the only reliable answer is to recover the charge, weigh it on a calibrated scale, and compare against the nameplate. If it’s short, there’s a leak — and under F-Gas that leak must be found and repaired before any gas goes back in. Topping up a leaking system is illegal, and pointless: it’ll only leak out again.

Refrigeration too — on the same F-Gas certification.

Air conditioning and refrigeration sit under the same F-Gas certification and share most of the diagnostic skills, so the same engineer who services your AC can handle your fridges and freezers on the same visit. If you run a shop, restaurant, pub, care home or hotel with a mix of both, that’s one contractor instead of two — and I take on home fridge repairs as well.

See my commercial refrigeration page for cold rooms, display fridges and freezers, the faults I see most, and how I price it.

The compliance side, handled.

I’m F-Gas Register certified (FGAS ID FGAS2002910), with the company qualification covering installation, repair, maintenance, servicing and decommissioning of stationary air conditioning, refrigeration and heat-pump equipment — with no upper limit on system size or charge. F-Gas law places legal duties on the operator of equipment containing fluorinated refrigerants: leak checks at set intervals, record-keeping, and proper recovery during repair and decommissioning. I handle that compliance as part of standard PPM, so it’s one less thing on your desk.

Factory-trained on the big three — and I service the rest.

Factory-trained on Daikin, Mitsubishi Electric and Mitsubishi Heavy Industries, and I service and repair any make — Samsung, LG, Midea, Toshiba, Hitachi, Panasonic, Fujitsu and the less common ones too. The diagnostic principles are the same across manufacturers; the difference is knowing where each one hides its access panels, sensors and service ports. The same engineer also covers air-to-water heat pumps — see my heat pump repair page (air-to-air AC and air-to-water heat pumps share most of their technology).

Installs — what I take on.

I do take installs, but within limits. As one engineer I won’t take jobs where the units genuinely need two people to lift safely — for those I either bring in a trusted second pair of hands and quote accordingly, or, if it’s really a job for an install team, I’ll tell you so.

On price, the install market is very competitive — much of it from firms running crews where one lead engineer makes the decisions and the rest fit at lower rates, which I can’t match as a single engineer doing the whole job. What I offer instead is the same engineer designing, installing and commissioning end to end, which matters most on awkward sites and on systems that still need to perform years later. Every install is quoted individually.