Shortly I will be replacing the condenser and compressor to condenser hose on my Focus.

Best advice is to apply a little PAG oil to the seals before tightening up the joints.

Now I don't have a supply of this oil in my garage and to buy 250ml for a tenner off ebay just to get 2 or 3 ml seems a bit extravagant especially as I have no other use for it.

The question is, what is a suitable alternative which will not rot the seals or upset the added gas and compressor oil when the system is charged.

I'ii bet WD40 or ordinary engine oil is out of the question.

Any advice please?

ScaniaPBman.

PS. For those purists amongst you, there is no residual gas in the system and I will get the neighbourhood air con expert in with his kit to finish the job.

Personally for the tiny amount needed on the seals I'd use 'Fairy Liquid' not oil.

A little googling suggests that PAG oil is actually not a good idea for o-rings as apparently it absorbs moisture from the air which can then corrode the parts the oil is in contact with. WD40 is not recommended because as a solvent it may end up drying out and damaging the o-rings. The recommendation is to use mineral oil.

However, according to wikipedia mineral oil is made of alkanes, is thus a hydrocarbon, and hydrocarbons are not good for rubber, initially softening and increasing flexibility but then attacking it. There are two exceptions, nitrile and viton rubbers are resistant to this. So whether or not mineral oil is a good idea to use on o-rings actually seems to depend upon what type of rubber they're made of.

There's a suggestion here that a drop of washing up liquid should be used, as coincidentally unofix has just happened to also suggest right before I finished writing my reply. 🙃

9 minutes ago, rd457 said:

as coincidentally unofix has just happened to also suggest right before I finished writing my reply.

You need to type faster 🤣

Many major engineering projects use Fairy Liquid as a lubrication on rubber type material since it does not react.