Welding experts?? - Harmattan
Very stupidly I pierced a tiny hole in SWMBO's Honda air con condenser by leaving a spark plug tool lying around. The local aircon specialists reluctantly agreed to get someone to have a go at resealing with a weld since the cost of replacement (if they can find a condenser)is probably as much as the car is worth. After £50 worth of trying they called a halt because nitrogen testing showed pinprick leakage through all three welds tried. The welder (from a different company) wasn't present to explain further. My question is whether there is a welding process that might provide a gas tight seal since the problem seems to lie with the porosity of the materials used.

If it can be resolved I'm keen to do so before seals start drying out since they are not ideally suited to the replacement refrigerant in any case. Otherwise, it's back to opening the window.
Welding experts?? - frostbite
Someone is bound to shoot me down on this. but I wonder whether duct tape would solve this problem if it is just a pin-prick hole?

Taking cover......
Welding experts?? - Dynamic Dave
Instead of welding, could it not be brazed with silver solder?
Welding experts?? - Mondaywoe
Araldite? Araldite reinforced with some aluminium mesh?

Must admit, I've never clapped eyes on a condensor. What is it made of? How thick?

Welding experts?? - 547HEW

I would suggest an application of Loctite 290. This is an engineering adhesive that penetrates pin prick holes in castings.

The holes have to be reasonably clean, then this stuff will wick into whatever fissures are there, and set solid. It is a cynoacrylate, i.e. anerobic, goes off in the absence of air, has a viscosity slightly greater than penetrating oil. I daresay you'll find details of it on the Loctite website.

Good luck.
Welding experts?? - Mondaywoe
Could always crack an egg into the system........Should make for interesting results!

Welding experts?? - Marcos{P}
I presume that when you say the condenser you mean the condenser coil?
If so the only way to attempt to block the hole is to use some silver solder as already mentioned. This should work but if not then you just change the coil. Normally very cheap.
Welding experts?? - Peter D
I'm with dynamic Dave here a silver solder fix is the only viable solution. However after over heating the system with a weld a lot of clening up will be required before a clean flux ( Boraz ) silver solder patch will take fix the problem. Done that been there Good Luck, Peter.
Welding experts?? - Dave N
The ally used for condensors is extremely thin (and cheap material)and has a very low melting point, therefore only specialist brazing and flux can be used with a propane torch. Even then, the melting point of the rod is only slightly lower than the ally, so care has to be taken. As far as I know, the rods are only available from the US, and the kit costs about as much as a new condensor.

I have used it and it works very well, but it is tricky getting something like a condensor, designed to dissipate heat, to just the right temperature to work. Even more so after a few other cack-handed attempts! A few seconds to long with the heat and it all disappears before your eyes like a fag end on a crisp packet. Silver solder won't take to the ally, and don't even thing about eggs/glue/tape, as the condensor runs at up to 30bar (450 psi).

Let me know what car it is and I'll see if any condensors are available at a reasonable price.
Welding experts?? - Dizzy {P}
If the wall of the condenser was reasonably thick, I would have gone along with 547HEW and tried Loctite 290. However, this is obviously out of the question with thin-wall "ally".

(Dave N -- purely for my interest/education, do you know if it's an aluminium alloy, or could it be a zinc alloy, Mazak for example.)

Probably too late now, and might not have been possible anyway, but it is often possible to plug a pin-prick hole in a thin-wall component with a self-tapping screw. Pushing a nail or similar into the hole first helps to form a wall for the screw to bite into. As I said, probably no good this time, but might be worth remembering for other occasions.
Welding experts?? - Harmattan
The car is a 1988 Honda Legend 2.7 coupe. The aircon people couldn't find a listing in their catalogue for it but estimated a minimum of £250-300 cost for the condenser plus the replacement materials and labour. Of course, they also pointed out that introducing the new refrigerant to a system presumably designed for R12 carries the risk of weeping seals and uncovering system corrosion so making a £500 + VAT repair of questionable value when the windows and sunroof still open for nothing. There's a Legend with everything working, including aircon, for sale locally for £900!

The weld appears to have 'taken' but the nitrogen test showed pinprick edge leakage. The Loctite 290 seems rather useful for a number of applications but doesn't seem to match the pressure requirement and who knows what the reaction would be when it meets R134a refrigerant.

My next investment is in one of those metal dishes with a magnetised base for keeping any small bits and pieces from rolling about and getting 'lost'in the engine compartment causing small disasters like this.

PS: My American Chilton manual for the Legend says I could be fined up to $25,000 for discharging R12 into the atmosphere in an uncontrolled manner. Oops!

Welding experts?? - Another John H
I'd be inclined to second the Araldite fix.

They stick people carrying aeroplanes together with it - a selection of small holes in alloy should be no problem, given a clean, grease free, surface. (roughening the surface with fine wet and dry before applying the glue wouldn't hurt, either.)

Just my 1p worth.
Welding experts?? - OldOiler
The Molecules of the gas are very small and will penetrate most DIY repairs and fail!!.
Try loc tite 270 or go to their web site for advice, alternativly find a good refridgerant engineer to make a duplicate part. good luck

Value my car