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 this 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. Even if it doesn't get to this very rare bad stage the presence of moisture internally will start corrosion and probably leaks as the moisture mixes with parts of the refrigerant to cause acids which then try to eat their way out.

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.

The majority of newer cars are using a condenser which also incorporates the drier so that although in theory it is possible to replace the drier element easily, in practice we find that most are impracticable to change and leave with confidence that they will not leak. In any case we find that unless there has been problems with moisture or there has been major component replacements then there is little point in replacing a drier less than six or seven years old. This is purely our own findings and does not agree with the theory. One advantage is that with the integrated drier a system requiring a new condenser also receives a new drier which is just as it should be. Another advantage with the integrated drier is that that is possible to increase the performance of the AC by re-routing the liquid refrigerant back into the bottom of the condenser to further cool the liquid (Sub-cooled Condenser).

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 £25 but a few specialised ones like some BMW receiver/dryers are more expensive. If you expect about £45 you won't be too far out and you may be happily surprised.
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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