Chemical washes and overhauls involve everything from standard general servicing plus cleaning the fan coil with a strong alkaline chemical to remove dust or mould that are stuck inside the coil. This greatly improves the cooling capacity of the aircon if there is a build-up of debris inside the coil, and the cooling ability of the aircon is generally considerably stronger after chemical cleaning.
An overhaul involves dismantling the aircon completely off the wall so that we can clean each compartment individually. We do not recommend overhaul for units older than 10 years, as the plastic can become brittle and it is a breakage hazard when we dismantle it.
Chemical wash is fine for units of all ages. Both types of chemical cleaning are very thorough and we recommend them mostly for air conditioners that are used very often and haven't been serviced in a while, or an aircon that isn't as cold anymore.