Split System Air Conditioning Installation
A split system is only as good as its installation. Get the siting, pipework, evacuation and charge right and it runs quietly for years; cut corners on the pressure test or the vacuum and you've built in a leak or a fault before it ever cools a room.
A split system pairs an indoor unit with an outdoor condensing unit, joined by refrigerant pipework, cabling and a condensate drain. The install looks straightforward, but the parts that decide reliability — a clean vacuum, a leak-tight joint, the right charge — are exactly the parts a rushed job skips.
This guide walks through a split installation in the order you'd actually do it: siting the units, running and insulating the pipework, the electrical connection, pressure testing, evacuation and charging, condensate drainage, and finally commissioning and handover.
Key takeaways
- Site both units for airflow, access, drainage and the shortest sensible pipe run.
- Refrigerant pipework must be clean, correctly sized and fully insulated end to end.
- Pressure-test for leaks and evacuate to a proper vacuum before you release any charge.
- Charge to the manufacturer's figure, allowing for pipe length, and record the readings.
- Commission against the design, then hand over with the record and user instructions.
Siting the indoor and outdoor units
Position the indoor unit for good air distribution across the room, clear of obstructions and away from beds or desks where a direct draught is unwelcome, with room for the condensate drain to fall away. The outdoor unit needs free airflow around the coil, enough clearance for service access, a solid level mounting, and a location that keeps noise away from windows and neighbours.
Plan the pipe run between them at the same time. The shortest practical route with the fewest bends keeps performance up and refrigerant charge sensible, and settling the drainage fall now avoids a condensate problem later.
Pipe runs, insulation and electrics
Run the refrigerant pipes clean and correctly sized for the unit, keeping the ends capped until connection so nothing gets in. Make flare or brazed joints properly, support the pipework, and insulate both lines fully along their whole length — poor or missing insulation causes condensation, dripping and lost capacity.
The electrical supply must be correctly rated, isolated and connected to the manufacturer's specification and the wiring regulations, with the interconnecting control cabling run alongside the pipework. Get the electrics and the pipe route settled together so nothing has to be redone.
Pressure test, evacuation and charging
Before any refrigerant enters the pipework, pressure-test the joints for leaks — typically with dry nitrogen — so a leak is found now, not after commissioning. A joint that passes here won't be weeping refrigerant in six months.
Then evacuate the pipework and indoor unit with a vacuum pump to remove air and moisture, and hold the vacuum to confirm it's tight and dry. Only then release or add the charge, following the manufacturer's figure and allowing for the pipe length. A poor vacuum or an incorrect charge is one of the most common causes of underperformance and early failure.
Never skip the vacuum
Air and moisture left in the system cause acid formation, blockages and lost performance. Pull a proper vacuum and confirm it holds before charging — it's the step that separates a lasting install from a callback.
Drainage, commissioning and handover
Confirm the condensate drain runs away with a continuous fall and discharges somewhere sensible, then check it actually flows — a blocked or back-falling drain is a classic cause of water damage. With the system running, take your commissioning readings: temperatures, pressures and operation across the modes, checked against the design and the manufacturer's data.
Finish by handing over: show the customer how to run and clean the unit, leave the instructions and warranty details, and issue the commissioning record. That record is your evidence the system was installed and set up correctly, and the reference point for any future service.
Capture the commissioning record on site
Recording the readings and issuing the commissioning record from TradePlanr on the day means the customer gets their paperwork immediately and you keep the evidence the job was done right.
Frequently asked questions
Why does a split system need evacuating before charging?
Evacuating with a vacuum pump removes air and moisture from the pipework and indoor unit. Left in, they cause acid formation, blockages, corrosion and lost performance, so you pull a vacuum and confirm it holds before releasing any refrigerant charge.
How important is the condensate drain on an air conditioner?
Very. The indoor unit produces condensate that must drain away with a continuous fall to a sensible discharge point. A blocked or back-falling drain is a common cause of water leaks and damage, so it's checked for flow at commissioning.
What readings are taken when commissioning a split system?
Typically operating temperatures and pressures and correct operation across the modes, checked against the manufacturer's data and the design. The readings are recorded on the commissioning record as evidence the system was set up correctly.
From guidance to action
Related guides
What Size Air Conditioning Unit Do I Need?
How to size a room air conditioner from floor area, heat gains and glazing — with a rule-of-thumb table and the proper method.
Air Conditioning Refrigerant Types (R32, R410A, R290)
The refrigerants used in modern air conditioning, their GWP and flammability class, and why the industry is moving to R32 and R290.
How Much to Charge for Air Con Installation (UK 2026)
What air con installers charge in 2026, what drives the price, and how to price installs and servicing to protect your margin.
