I know that it needs occasional recharging but is there anything else that needs doing?

Yes very occasionally. The biggest enemy of AC is moisture within the system with the refrigerant but don't confuse with the water that is produced by the system when it is working well and drips out under the car. The oil used in AC systems is hygroscopic and will absorb moisture if it gets the chance - just like the brake fluid in the braking system.. Obviously any free moisture floating around in the system will sooner or later get to the place where the cold is produced and will promptly freeze into a chunk of ice thus stopping the AC working. As the evaporator defrosts it will flood the windscreen with moisture and mist up the screen,then after a couple of minutes the chunk of ice will melt and the AC will resume working again which will quickly demist the screen and then that blessed bit of moisture will freeze up again and restart the cycle.

Every AC system has a container, which has a bag of desiccant in it to absorb any free moisture. Depending on the design of the system this container is either a receiver/dryer or an accumulator. These are intended to be replaced on a regular basis, rather like an oil filter but perhaps not so frequently.

If the system should develop a fault it is probably worth replacing this dryer when the fault is cleared but if there is no fault then replacing perhaps each alternate recharge would be prudent - that is, about every six years. This is because the desiccant is gradually absorbing moisture that has entered the system and after a time it reaches the limit of it's capacity - and it is important not to approach too close to that limit. A few models have driers placed in such inaccessable places that replacing the drier is quite a lengthy job - in these cases maybe it could last perhaps three recharges before being replaced, but don't forget it altogether.

If the drier is really quite old the desiccant can sometime break down and circulate with the refrigerant and eventually clog the expansion valve. This is quite common on the older Jaguars with the long horizontal receiver/drier and manifests itself by the lack of coldness out of the vents but the expansion valve glowing with hoar frost.

Some of the common driers are only just over£20 but a few specialised ones like some BMW receiver/dryers are more expensive. If you expect about £40 you won't be too far out and you may be happily surprised. A few models produced since about 1998 are incorporating this drier element into the construction of the condenser which has the advantage that when the condenser is replaced after say an accident that the drier is replaced as well (as it ought to be), but does create complications for routine drier replacement in the future - it could be that the manufacturers have used a much larger quantity of desiccant than usual, I do not know about this at present. Some of these which in theory have a replaceable desiccant sac are virtually impossible to change in practice. Some others of these integrated driers are completely impossible to change the dessicant and will necessitate a complete change of the whole condenser/receiver/drier assembly.

An even newer development is that there are cars now out which have a combined condenser/radiator assembly which will mean that in the event of a failure of either component, both will need replacement - that is a leaking water radiator will necessitate the recovery of the refrigerant, the replacement of the whole assembly and the recharging of the AC system.

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