KEYWORD: split system upgrade path
BODY:
Moving from a 2.5 kW split system to a 5 kW unit during a renovation often creates one immediate fear: do we need to run a new circuit? Not always. The split system upgrade path from 2.5 kW to 5 kW without rewiring is possible when the existing supply cable and breaker have enough headroom. Instead of pulling new cable through walls and ceilings, a licensed technician can change the relay board, replace the overload relay, and adjust the outdoor PCB jumpers to match the larger unit. This keeps the upgrade faster, cheaper, and less disruptive while still giving you double the cooling capacity.
Word count maybe 100. Good.
H2: Check circuit capacity first
Before any relay board work starts, the existing circuit must be assessed. Many older 2.5 kW installs in Melbourne houses use 2.5 mm² two-core and earth cable protected by a 16 A breaker. That can often carry a modern 5 kW inverter without issue because the running current is well under 10 A. If the cable is only 1.5 mm² or the breaker is 10 A, the split system upgrade path without rewiring stops there. No relay board change can safely fix undersized cable.
A licensed refrigeration mechanic will measure insulation resistance, check the RCD, and confirm the maximum demand on the circuit. If the circuit only serves the air conditioner, the job is straightforward. If other outlets or a second appliance share the circuit, the upgrade may still work, but the tech must calculate total load first.
Word count around 150.
H2: Choose the right 5 kW unit
Not all 5 kW units are equal when you want to avoid rewiring. Fixed-speed models draw a high locked-rotor current at start-up, which can trip a 16 A breaker even if the cable is safe. Inverter models use soft-start control, so the compressor ramps up slowly and stays within the circuit rating. When selecting the unit, check the maximum running current and the minimum circuit ampacity on the outdoor unit nameplate. A 5 kW inverter with a maximum input current of 7.5 A will sit comfortably on a 16 A circuit. A unit with a 12 A maximum will not.
The indoor fan relay must also match the new unit. A 5 kW indoor unit often has a larger fan motor than a 2.5 kW unit, so the relay board may need a higher-rated fan relay even though the supply cable stays the same. Keep this in mind before ordering the unit.
Word count maybe 130.
H2: Split system upgrade path steps
The actual relay board changes are done after the old unit is pumped down and disconnected. These steps assume the original circuit has already passed inspection and the new 5 kW unit is approved for the existing breaker.
Isolate and recover refrigerant
The old 2.5 kW system is pumped down to store refrigerant in the outdoor coil. The technician isolates the isolator at the outdoor unit and removes the indoor and outdoor electrical connections. The existing interconnecting cable can stay in place if its size matches the new unit. This is what avoids the need for new wiring.
Replace the overload relay
The compressor overload relay on the old outdoor board is set for the 2.5 kW compressor’s current draw. A 5 kW compressor pulls more current, so the overload relay must be replaced or its dial adjusted to the new full-load amps. This prevents nuisance tripping and protects the compressor from overheating. The contactor is also checked; if it is rated below 20 A, it is swapped for a 20 A contactor.
Change outdoor PCB jumpers
Most inverter outdoor boards use DIP switches or jumpers to identify compressor capacity. The technician moves the jumper from the 2.5 kW position to the 5 kW position according to the manufacturer’s table. On some models this is a small plug on the relay board; on others it is a software setting entered through the service tool. Getting this wrong causes the unit to run at the wrong compressor frequency, which defeats the upgrade path and can damage the new compressor.
Test current draw and limits
After the new unit is connected, the technician runs the system in cooling and heating at full load. A clamp meter measures the running current at the breaker. The reading should stay below 80 per cent of the breaker rating. The tech also checks the voltage drop under start-up and feels for heat at the terminals. If the current draw stays within limits and the RCD holds, the split system upgrade path is complete without any new circuit.
Word count maybe 220.
H2: When rewiring is still required
This upgrade path is not a workaround for a weak circuit. If the existing cable is 1.5 mm², if the breaker is 10 A, if the voltage drop exceeds the allowed limit, or if the new unit’s minimum circuit ampacity is above the existing cable rating, the circuit must be rewired. A relay board change cannot increase cable capacity. In those cases, running a new dedicated circuit is the safe and compliant option. Trying to avoid it by adjusting a relay or jumper creates a fire risk and voids the unit warranty.
Word count 100.
H2: Why this wins for renovations
For Melbourne homeowners and small businesses renovating a single room or converting a garage, doubling capacity from 2.5 kW to 5 kW without rewiring saves hundreds of dollars in cable, labour, and wall repairs. The split system upgrade path avoids cutting access holes, lifting roof sheets, or patching plaster. The old interconnecting cable stays in place, and the relay board changes take a few hours instead of a full day.
More importantly, a properly adjusted relay board and overload relay mean the new 5 kW unit starts softly, runs within the circuit limit, and does not trip the breaker on hot days. That reliability is what makes the upgrade worthwhile. If the unit is installed incorrectly, you get callbacks, high running costs, and a compressor that fails early. Done right, the same circuit supports years of effective cooling.
Word count 120.
Maybe add final short paragraph:
If you are planning this upgrade, have a licensed Melbourne technician inspect the circuit before you buy the 5 kW unit. A five-minute check of the cable size, breaker rating, and existing relay board tells you whether the no-rewire path is open. Then the technician can carry out the relay board changes safely and commission the system to manufacturer settings.
Word count 60.
Total maybe 850? Need ensure 900-1300. Let’s count more precisely.
Intro: about 105 words.
H2
