I will be installing the r134a conversion kit into my 1990 240 soon.I think most leaks originate at the fittings so as added insurance I was going to add teflon tape to the fittings. Do you think it's a good idea or not necessary?
Also as a side note,I was talking to my dad who met an ac repair fellow in florida. The man told him that most of the shops that do the quick conversions,evacuate and change the fitiings are responsible for causing a leak.He said some places put the new fittings on top of the old ones WITHOUT removing the old schraeder valves.So the new valve doesn't seat properly onto the old valve and you eventually lose all the freon.You can't have 2 schraeder valves on top of each other.Sounds legit to me!Thanks,
Nelson

Some of the retro kits have a new 134a valve that fits on top of the old r12 valve, but you are supposed to remove the old core with a core tool and then screw on the new.
If you want something to help seal and lube the fittings and o-rings, use Nylog.
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Gary Gilliam Sumerduck VA, '94 940 na Regina 160k '86 240 190k

Don't use Teflon tape, use new o-rings on the fittings.
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john

Interesting,
Never heard of a shop adding teflon tape to fittings. I think the fittings are flared in addition to the O-rings. As an aside, a plumber once asked me why I was adding teflon to a flared fitting. If you need teflon, the connection is no good to begin with according to him. Don't know if that helps.
Schraeder valves? Why not change them since the system is open anyway? I'm not sure why you wouldn't.
How come you are converting? The AC guy I used recommended against it. He said the R12 did a better job cooling in a system designed for R12 than using R134A in a system designed for R12.
I haven't had any bad issues with my R12. I know it costs more, something like $60 a pound rings a bell, but it does cool well.
Just my 2 cents.
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'60 544, '68 220S, '70 145S, '72 144E, '86 745T

Many leaks occur at o-rings or fittings, so your ac friend is correct. I had just this situation and ended up replacing the entire pipe with the old fitting. Don't use Teflon tape. Refrigerant causes Teflon to soften and fray and little pieces will break off to clog the expansion device. The teflon tape will also buffer threaded connections to cause bridging [a gap]on a o-ring fastener and other types of compression seals.

Adding tape to o-ringed line fittings is asking for trouble, I think. You might be right that the fittings and valves have to be thought about. Some conversion fittings are made to depress the old schrader, but failing to check will make charging difficult in some cases and in others, might cause leaks.

Thanks to all for your advice,no teflon.New issue,see new post.Thanks