Very occasionally secondhand aircon parts are a viable option.
It would be fair to say that if any pipe has been rubbing and has worn through that a secondhand one would be acceptable but always check with an AC professional first as some pipes are repairable, sometimes very economically. If a pipe fails for another reason be wary, some are known to professionals as weakspots and a secondhand one could easily have the same weakness. Pipes being retained under clips frequently become corroded and eventually leak so carefully inspect any replacement pipe for the same problem. Cars with AC in the rear as well as the front frequently have issues with leaks in the pipes - often these are repairable.
I would always suggest that you check the price of new or possibly reconditioned parts with the main dealers and also alternative suppliers such as AC professionals before buying secondhand, sometimes they are surprisingly inexpensive but then again sometimes impossibly overpriced. The suction/discharge hose on the 2001 to 2006 Mondeo is an example, the original pipe often rubbed through on the subframe but a redesigned pipe to clear the subframe is quite reasonably priced - full marks to Ford!
Buying a secondhand receiver/drier would in 99.9% of cases be very bad practice. Apart from a mere handful of models, they are still available or a suitable substitute can be found. I had to make up pipework a year or two ago in order to replace a drier on a Ford Probe as the original is no longer available from Ford or anywhere else it seems. If a secondhand drier had been available it might have been acceptable in this case. I have since been informed that I can now get a new Probe drier from a company which imports them from Australia - see the links page.
Buying secondhand condensers would normally represent a poor bargain but there are still a few occasions when it might be acceptable, for example when only a manufacturers part is available (usually at high cost) and the car is very elderly.
Secondhand compressors are probably the most commonly traded component in the AC system. If properly looked after a compressor has a very long life (one of our vehicles, with a very ordinary AC compressor, had completed three quarter of a million kilometres and was still operating faultlessly when the vehicle was sold). If the aircon system is neglected or the owner is unlucky to have a fault develop and the compressor fails then in some cases a secondhand compressor might be a suitable replacement. Always check the condition of the oil in the pipework carefully as sometimes compressors break down badly leaving a trail of small metal particles all around the system. If the compressor is replaced with either new or secondhand with those metal particles still in the system the replacement compressor is almost certainly going to be wrecked by those particles and a warranty claim will be dismissed. Always check the price of new compressor first, I have supplied a brand new compressor for a Ferrari for under £200 but I have also had to supply a compressor for a Mitsubishi for over £650.
How to find secondhand parts? Try the internet first, Autotrader is a good first stop, possibly Ebay, or www.247spares.co.uk, try the forum pages of your particular make or model or just try a search engine. Local papers usually have ads for general car breakers but there are also breakers who specialise in just Japanese cars or French cars or only Volvos or even just one particular model. Friday-Ads is not only a paper but is also available on-line and could be useful.
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Thank you for staying the course. I hope that you found some of it useful.
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