Chemical Wash (without dismantle fancoil unit)
- is done using the hanging tray method whereby only the front cover and the filter is removed and a tray is hanged below the fancoil unit and chemical wash done at the unit itself. This method is not exactly wrong but the wash will not be thorough enough to reach the water tray behind to get rid of the dirt and jelly. As time goes by the dirt and jelly will build up and lead to leaking.

Also there are risk that the pcb board and the motor at the side can be damaged by the chemical. As this method involves lesser work to dismantle the unit, the charges will be lower.

Chemical Overhaul (with dismantle fancoil unit)
-involves dismantling the whole unit and bringing the parts to the toilet for chemical wash. This will thoroughly clean the aircon unit and clear all the jelly and grime from the water tray.

This is the thorough way of doing a chemical procedure and because it involves dismantling the unit, the term Overhaul is used instead of Wash. As this requires more work, naturally the price will be higher than chemical wash.