Multi-split with one outdoor unit and 4 indoor units — do we sanitise them all at once or one by one?
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We have a multi-split system (Mitsubishi) with a single outdoor unit on the balcony and 4 indoor wall units, one per room, in a flat in Titan. The installer told us the outdoor unit is 'shared' by all of them. When we call someone for sanitising, is it done once for all 4, or each room separately in different visits? And is the shared outdoor unit cleaned once or 4 times?
What is really happening
Every indoor unit in a system — even ones connected to the same outdoor unit — develops its own microbial community, depending on humidity, temperature and age, just like separate standalone units; there is no 'collective cleaning effect' from sharing a compressor. Fouling of the outdoor condenser reduces the capacity and efficiency of the whole system, regardless of how many indoor units it feeds, which is why it gets a single check, but washing each indoor evaporator stays separate.
- Each indoor unit has its own filters and surfaces to maintain.
- Connections to the shared unit are shown schematically.
- One outdoor unit serves several indoor units.
- Bacterial and fungal load of air-conditioning systems varies with operating regime, and quantitative microbial risk assessment shows relevant exposure for occupants. [Journal of Aerosol Science, 2024]
- Fouling of the outdoor condenser raises pressure drop and condensing pressure, reducing the split unit's capacity and efficiency. [Science and Technology for the Built Env, 2019]
- Cooling coils host bacterial and fungal communities whose load depends on climate, humidity and maintenance. [Indoor Air / PubMed, 2020]
What we do on site
- Each of the 4 indoor units: sealed double cover, alkaline detergent, adjustable pressure wash of its own evaporator, roller, pan and hose, fragrance-free sanitising, own filters.
- Shared outdoor unit: checked, condenser coil washed externally if needed, once for the whole system.
- All in the same visit, room by room, roughly 3 hours for 4 indoor units plus the outdoor one.
- See current rates on the Prices page.
What you can do yourself
- Each room with its own filters cleaned every two weeks, regardless of how often that room is used.
- Check the outdoor unit visually twice a year — dust, leaves, obstructions on the condenser grille.
What NOT to do
- Do not assume sanitising one indoor unit 'cleans the whole system' — the other 3 stay dirty separately.
- Do not charge (or accept) an outdoor unit fee 4 times for a multi-split system with a single compressor.
Prevention
See current rates on the Prices page.
When to call us
0764 012 943, WhatsApp, Monday–Saturday 08:00–20:00; we come once for the whole system in Titan.
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Sources (4)
The information on this page is educational and based on cited sources; it does not replace medical advice. We do not do repairs, installation or refrigerant circuit work.