Equipment installed on this project
Mijas Ducted Air Conditioning Replacement — Daikin to Johnson DC Inverter A++
How Agua Therm replaced an end-of-life Daikin concealed ducted AC system with a Johnson DC Inverter A++ R32 unit in a Mijas villa — keeping the existing rigid ductwork and ceiling diffuser, with full F-Gas refrigerant recovery, deep vacuum and professional commissioning.
The Problem: An End-of-Life Daikin Ducted System
The client, a homeowner in Mijas on the Costa del Sol, had a Daikin concealed ducted air conditioning system installed in the false ceiling void of the principal bathroom, distributing cooled and heated air throughout the private wing of the villa via concealed existing rigid ductwork and a ceiling supply diffuser. After many years of operation under Costa del Sol coastal conditions — long summers, salt-laden humidity, autumn lightning storms — the unit had reached the end of its practical service life. The homeowner reported intermittent performance, unusual compressor noise, short cycling, and a steadily rising electricity bill.
Original Daikin unit beyond its expected economic service life — repair cost approaching replacement cost
Degraded efficiency: older units running on R-410A (or earlier R-22) refrigerant operate well below modern A++ standards
Spare parts availability declining — discontinued legacy Daikin models have increasingly expensive and slow-to-source replacement parts
Original Daikin wired controller showing intermittent display and lagging response to setpoint changes
Increased outdoor compressor noise — typical symptom of worn bearings and degraded anti-vibration mounts
Client concerned about EU F-Gas regulation — older refrigerants are being progressively phased out across the EU
The Solution: Johnson DC Inverter A++ — Existing Ductwork Retained
Agua Therm specified a complete replacement of the Daikin equipment — outdoor unit, indoor concealed ducted unit, and wired controller — with a Johnson DC Inverter A++ system running R32 refrigerant. The critical decision was to retain the existing infrastructure that was in perfect condition: the existing rigid ductwork inside the ceiling void, the ceiling supply diffuser, the structural penetrations, and the condensate drain run. Only the refrigeration generation equipment and its controller were replaced. This dramatically reduces project time, cost, client disruption, and waste sent to landfill — and extracts the maximum return on the original ductwork investment, which typically represents 30–50% of a complete ducted system's installed cost.
Why Johnson — and Why This Specification for Mijas
The choice of new equipment was not arbitrary. Johnson is a brand widely available across the Spanish HVAC professional wholesale network, with national parts availability and technical support. For this installation specifically, the Johnson DC Inverter A++ range with R32 refrigerant was specified for the following technical and commercial reasons:
R32 has a global warming potential (GWP) of approximately 675, compared to 2,088 for the R-410A in the legacy Daikin unit. The EU F-Gas regulation is progressively phasing out high-GWP refrigerants. Specifying an R32 unit today guarantees compatibility with the next decade of regulation and stable pricing on future top-up charges.
The DC Inverter compressor modulates its speed continuously to maintain the target temperature, instead of starting and stopping like older ON/OFF compressors. This typically reduces real-world electrical consumption by 30–50% compared to the replaced Daikin unit (which was likely pre-Inverter or first-generation Inverter).
Johnson has a national distribution network in Spain. For a permanently occupied or holiday-let villa on the Costa del Sol this is critical — a fault in August is resolved in days, not weeks waiting for imported parts.
The Johnson concealed ducted indoor unit selected has external static pressure adequate for the existing rigid duct network and ceiling diffuser. Duct cross-section and total run length were verified before the model was specified, to guarantee correct airflow and noise levels.
For a pure equipment swap (where ductwork, diffuser and low-voltage cabling stay in place), specifying a quality mid-premium brand with strong wholesale discount allows us to deliver a brand-new A++ system with full warranty at a competitive price point versus a like-for-like new Daikin specification.
The Equipment Installed
Johnson DC Inverter A++ Outdoor Unit
Spec: Variable-speed DC Inverter compressor, R32 refrigerant, A++ energy label, white RAL-painted casing rated for coastal environments, large-diameter front axial fan for reduced sound levels.
Role: Provides cooling and heating capacity. Direct replacement for the legacy Daikin outdoor unit on the existing patio anti-vibration feet (inspected and re-rubbered).
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Johnson Concealed Ducted Indoor Unit
Spec: Low-profile ceiling-void chassis, centrifugal fan with adjustable external static pressure for rigid ductwork, single-phase electrical supply, condensate drip tray with optional pump.
Role: Generates the conditioned airflow and pushes it into the existing rigid duct network. Sized to fit the ceiling void footprint left by the original Daikin unit.
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Johnson Wired Wall Controller
Spec: Backlit blue LCD display, capacitive touch buttons: mode (M), fan speed, setpoint up/down, time scheduling, eco mode, power. Vane SWING control, screen lock.
Role: Wall-mounted wired controller in the corridor — direct replacement for the small-display legacy Daikin controller.
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New Copper Refrigerant Lineset and Flared Connections
Spec: New refrigeration-grade copper tube, manual eccentric flaring tool (45° flare angle) suitable for R32, brass cone nuts, torque-wrench tightening per manufacturer table.
Role: Connects the indoor unit to the outdoor unit. Lineset is fully renewed — the legacy Daikin lineset is NEVER reused, to prevent contamination of the legacy mineral oil being incompatible with the POE oil used in R32 systems.
The Installation Step by Step — 16 to 17 April 2026
The replacement was completed across two working days following a strict protocol that guarantees compliance with F-Gas regulation, integrity of the new system, and zero damage to the existing infrastructure being retained.
Recovery, Strip-Out and Preparation
- 1Initial inspection: confirm condition of the existing rigid ductwork, verify ceiling diffuser, check condensate drain and existing electrical supply.
- 2Complete electrical isolation of the legacy system at the main consumer unit — labelled and verified with multimeter for absence of voltage at the terminals (visible in the photo of the team working on the open outdoor unit).
- 3F-Gas compliant refrigerant recovery from the legacy Daikin system per EU Regulation 517/2014 — refrigerant is recovered into a certified, weighed cylinder and handed over to a licensed waste contractor. Refrigerant is NEVER vented to atmosphere.
- 4Open the bathroom false ceiling to access the legacy indoor unit. The photos show the existing false-ceiling sheet carefully opened around the diffuser to avoid damage.
- 5Strip-out of the legacy Daikin wired controller — disconnect control cable, mark polarity for reuse on the new Johnson controller.
- 6Strip-out of the legacy indoor unit: disconnect copper pipework, disconnect control wiring, disconnect condensate drain, lift the chassis out of the ceiling void with two operatives.
- 7Strip-out of the legacy outdoor unit on the patio — electrical disconnection, refrigeration disconnection (recovered), sack-truck removal.
- 8Clean the ceiling void and final inspection of the rigid duct and diffuser condition — both confirmed in perfect condition, ready to mate to the new equipment.
Installation, Commissioning and Handover
- 1Position the new Johnson indoor unit in the false ceiling — the photos show two Agua Therm technicians lifting the chassis onto its mounting blocks before final positioning. Anchored to the slab using threaded rod and chemical anchors.
- 2Connect the new indoor unit to the existing rigid duct via a certified flexible canvas connector — the canvas connector dampens fan vibration transmission from the centrifugal fan into the rigid ductwork and ceiling structure, eliminating structural noise.
- 3Reconnect condensate drain to the existing run — verify fall and water-test the discharge before continuing.
- 4Install the new Johnson outdoor unit on the patio anti-vibration feet — existing feet inspected and reused after verification, with new rubber pads fitted.
- 5Run new copper lineset: refrigeration-grade annealed copper tube, individually insulated with regulation-thickness elastomeric foam.
- 6Manual flare of all four connections (indoor gas, indoor liquid, outdoor gas, outdoor liquid) — visible in the photos. Flares are made with a calibrated eccentric flaring tool and visually inspected: the flare face must be smooth, bright, and free of cracks. Cone nuts torqued to manufacturer specification with a torque wrench.
- 7Nitrogen dry pressure test at 30 bar for a minimum of 30 minutes — verified with digital manometer for zero pressure drop (any drop indicates a leak that must be located and repaired before continuing).
- 8Deep vacuum on the refrigeration circuit using a two-stage rotary vane vacuum pump — the testo digital manifold gauge visible in the photos shows the vacuum reading during the process. Target is at least 500 microns (0.5 mbar) held for 30 minutes with no rise — this confirms all moisture and air have been evacuated from the circuit.
- 9Open the outdoor unit service valves — factory-precharged R32 refrigerant fills the complete circuit. If the lineset exceeds the standard pre-charge length, additional refrigerant is added per the manufacturer table.
- 10Final electrical connections: dedicated single-phase supply with dedicated MCB and RCD, communication cable between indoor and outdoor units, control cable to the new Johnson wall controller.
- 11Power up and self-test sequence. Verify cooling mode (photo shows controller in COOL mode at 21°C), heating mode, automatic mode, and dehumidification mode.
- 12Measure supply and return air temperature at the ceiling diffuser with a temperature probe to confirm correct delta-T (typically 8–12°C in cooling mode at a sensible setpoint).
- 13Client demonstration of the new Johnson controller, configuration of time schedule, explanation of maintenance (filters every 3 months) and handover of manual and F-Gas operation certificate.
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Why Keeping the Existing Ductwork Is the Right Decision
A common client question is: "Shouldn't we replace the ductwork too?" For this Mijas villa the technical answer was clear: NO. Here is the reasoning:
- The existing rigid ductwork was in perfect condition: no visible corrosion, no dents, sealed joints, intact external insulation. Properly installed rigid sheet metal duct has a 30+ year service life.
- Replacing the ductwork would have required opening large sections of the false ceiling, damaging the diffuser (which was perfectly integrated into the bathroom design), reinstating plasterboard and repainting — work that would multiply project cost and timeline by three or more.
- Rigid sheet metal ductwork has better acoustic performance and significantly higher durability than insulated flexible duct. Replacing good rigid duct with flexible would be a technical downgrade, not an upgrade.
- Sustainability: every metre of duct that isn't scrapped avoids landfill waste. Selective equipment replacement is the most sustainable option whenever the duct is in good condition.
- The client pays only for what they need: new equipment and installation labour, not an unnecessary structural refurbishment.
F-Gas Refrigerant Recovery: What the Law Requires and What We Do
EU Regulation 517/2014 (F-Gas) and its Spanish transposition under Real Decreto 115/2017 require that any operation on a refrigeration circuit containing fluorinated gas is carried out by an installer holding a valid professional certification (carné profesional) and following a documented recovery protocol. On this Mijas replacement:
The legacy Daikin refrigerant was recovered 100% using a professional recovery unit and a certified recovery cylinder weighed before and after.
Recovered refrigerant was handed over to a licensed hazardous waste contractor, with a delivery certificate filed in the client's project record.
The operation is logged in the F-Gas tracking system with weight recovered, responsible technician, date and refrigerant destination.
The client receives a copy of the F-Gas operation certificate — important for future technical inspections, property sale contracts, and any insurance claim.
Under no circumstances is refrigerant vented to the atmosphere. The administrative penalty for doing so can reach several thousand euros and the responsibility falls directly on the installer.
Installation Results
What Our Technical Team Says
"This kind of replacement is exactly the type of project that delivers the most real value to the client: the old equipment was finished, but the existing duct was perfect. By changing only the equipment we delivered a brand-new A++ R32 system in two days, with no ceiling demolition, no plastering work, and the client ends up with a modern unit on full manufacturer warranty for a fraction of what a complete new install would cost. The skill is knowing when the duct stays and when it doesn't — that takes experience and honesty with the client."
"On every equipment replacement we make a point of checking the electrical installation before powering the new system up. On this Mijas villa we verified the dedicated MCB and RCD were correctly sized for the new Johnson equipment, checked the supply cable cross-section and the earth continuity, and replaced the indoor-outdoor communication cable with a new run. The communication cable is something many installers reuse without thinking, but after years of salt air and UV on the Costa del Sol the conductors can be oxidised and give intermittent faults that are a nightmare to diagnose later."
Premium alternative · What we could also have installed
How Airzone could have enhanced this ducted AC installation
This Mijas villa chose a like-for-like ducted replacement: one ducted unit swapping for another, keeping the system as a single zone. That's a perfectly valid decision — and the most cost-effective one when the customer is happy with how the house behaves thermally. But the alternative we considered for this job is worth understanding: Airzone, a Spanish zoning and control system with its head office in Málaga (under 35 km from Mijas), which bolts directly onto ducted units like the newly installed Johnson DC Inverter A++.
As accredited Airzone installers on the Costa del Sol (the system features in our Mijas Airzone Flexa UFH 2025 case study), we know the three product paths that apply to a ducted unit like the one in this home. Each solves a different problem.
A pocket-sized Wi-Fi adapter that connects to the indoor unit via dedicated bus or IR. Keeps the system as a single zone but adds control from the Airzone Cloud app, Alexa, Google Assistant and Apple HomeKit.
Supports KNX, Modbus and BACnet integration for villa-grade home automation.
A factory pre-built motorised plenum that bolts directly onto the ducted unit. Enables up to 8 independent zones, each with its own motorised damper and thermostat. The plenum boxes are manufactured to fit the indoor unit model — including the Johnson DC Inverter R32 range — and bolt up in a matter of hours.
The existing rigid ductwork we retained in this job is ideal for damper-based air distribution.
Main Flexa control board with individual dampers per room, wired or RF thermostats (Lite, Think, Blueface) and optional modules to combine the ducted unit with underfloor heating, aerothermal or DHW. The option for villas that want a single climate brain.
Blueface and Think thermostats hold eu.bac certification for control performance.
Quantifiable benefits of adding Airzone
Why Airzone is a technical fit for this project
The existing rigid ductwork we retained in this Mijas villa holds its shape under an added back-pressure of 5–15 Pa — the exact range introduced by Airzone's motorised dampers. The new Johnson DC Inverter A++ R32 already integrates a modulating EC fan, capable of dynamically compensating for the pressure change when zones close. And the electrical board we installed meets the isolation and cable-section requirements to add a 24 V transformer (the supply that powers the Easyzone central board).
Considering Airzone for your home?
We provide no-obligation technical surveys for Aidoo Pro, Easyzone and Flexa 4.0 on new or existing ducted installations in Mijas, Marbella and across the Costa del Sol.
Request an Airzone quoteSources: Airzone (airzonecontrol.com) · European Building Automation and Control Association — eu.bac · Universidad de Córdoba · KNX Association. Savings figures published by the manufacturer; actual performance depends on the home, occupancy patterns and setpoints.
Coverage: Mijas and the Whole Costa del Sol
Agua Therm provides ducted air conditioning installation and replacement services across Mijas — including Mijas Pueblo, Mijas Costa, La Cala de Mijas, Las Lagunas, Calahonda, El Chaparral and Riviera del Sol — and across the entire Costa del Sol from Estepona to Málaga city. We work in villas, penthouses, apartments and commercial premises. Every project starts with a free site survey and a detailed written quotation. Subject to site survey.
Agua Therm installs and replaces ducted air conditioning systems in Mijas Pueblo, Mijas Costa, La Cala de Mijas, Las Lagunas, Calahonda, El Chaparral, Riviera del Sol and across the Costa del Sol.
Frequently Asked Questions — Ducted AC Replacement in Mijas
Manufacturers, Standards & Official Sources
On this installation we work exclusively with internationally recognised manufacturers and in full compliance with current European and Spanish regulation. For full transparency and verification, we link below to the official sources for each manufacturer of equipment or instrumentation used on this project, as well as the applicable legal texts:
International parent group of the Johnson air conditioning brand. Official A++ DC Inverter R32 range specifications.
Spanish subsidiary of Daikin Industries. Technical information, manuals and official service network for the original Daikin equipment replaced.
German manufacturer of the digital manifold gauge and vacuum equipment used for the nitrogen pressure test and deep vacuum on the refrigeration circuit.
Daikin Europe's official technical page on R32 refrigerant: GWP approximately 675, thermodynamic properties and POE oil compatibility.
Consolidated text of the European Regulation on fluorinated greenhouse gases, published by EUR-Lex (EU Publications Office).
Spanish Royal Decree regulating the marketing and handling of fluorinated gases and equipment based on them in Spain. Published in the official state gazette (BOE).
Spanish association of refrigeration companies and technologies — sector body for commercial/industrial refrigeration, refrigerant recovery and professional training.
European Commission's official page on energy labelling for air conditioners, definition of the A+++ to G range and SEER/SCOP calculation methodology.
External links open in a new tab. Agua Therm is an independent installer and does not officially represent any of the manufacturers cited — the links are provided solely as verifiable technical reference.
Also see
About the Author
Ben Hayden
English-Speaking Electrician & Independent Energy Advisor
Ben Hayden is an English speaking electrician and independent energy advisor based in Marbella, Spain, with over 15 years of electrical experience across Europe. He provides independent energy and electrical checks for overseas property owners and managers across the Costa del Sol — helping clients cut electricity bills, navigate Spanish regulations, and make confident decisions on solar PV, heat pump, EV charger and battery storage projects.
Ben advises in plain English on projects where the paperwork is in Spanish and the stakes are high. His writing has appeared in ExpatArrivals, The Olive Press, Euro Weekly News, BuildingTalk and pv magazine.
Need to Replace Your Ducted Air Conditioning in Mijas?
Agua Therm replaces ducted air conditioning systems in Mijas and across the Costa del Sol. Johnson, Daikin, Mitsubishi Electric, Fujitsu, LG and Samsung — professional installation with certified F-Gas recovery, pressure test, deep vacuum and full commissioning. Free site survey and fixed written quotation. Subject to site survey.