Automotive Air Conditioning Information Forum

I'm the proud (?) owner of a 1989 Peugeot 405 Mi16, and need some advice on a bit of a saga that I've been going through with its air conditioning. Long story short, I'm looking for advice on how much oil to add to compensate for a fairly large persistent leak. There's a fair bit of backstory though, so if you don't mind listening to me rambling, here goes:

The previous owner converted the original R12 AC system to R134a, with new condenser, compressor, receiver-dryer and TXV. It worked REALLY well when I bought the car - by far the best-cooling R134a conversion I've seen - but after a few months of ownership, I noticed oil dripping from the condenser inlet fitting, and unsurprisingly, about a week later, the AC stopped working. I spoke to the previous owner and he confirmed the details of the R134a conversion and told me that it had never needed any top-ups since he converted it 2 years prior.

I'm a decently competent DIY mechanic and usually work on my own cars, but since it was going to need refrigerant recovery, I took it to a local shop. They refused to touch it, claiming that it still had R12 service ports. This was complete nonsense as I'd seen the ports with my own eyes and there were definitely R134a-style quick-disconnect adapters on them, but I assumed they were just making an excuse to not work on an old car with converted AC, so I left it at that. A while later I noticed that they had REMOVED the service port adapters, presumably venting the refrigerant and leaving the system open to atmosphere (since the R12 ports had their valve cores removed when the adapters were installed). Yikes! Not doing business with them again.

After that disaster, I made an appointment at an AC specialist, who replaced a torn o-ring on the condenser inlet fitting, recharged the system, and gave it a clean bill of health. However, within a year, it had leaked down again, with oil drips coming from the same fitting, and at this point there's no measurable pressure left in the system.

While the specialist shop was competent and easy to deal with, they were *not* cheap, and I can't afford to keep going back to them, especially not for time-consuming leak-hunting work. So this time since there's no refrigerant to recover, I've decided to DIY it. I've never worked on AC before, but I've read a few books on automotive AC and have a reasonable grasp on the theory. I've got myself a gauge set and vacuum pump, and plan on using straight R134a, not the nasty auto-parts-store stuff.

So where we're at right now is:

• No pressure in refrigerant circuit - gauges read 0.

• Visible oil deposits and lots of dye around condenser inlet fitting.

• UV light shows dye around pressure switch and service ports.

• Hoses and system components appear to be intact.

• System was left open in humid weather for ~2 weeks between visits to first and second shops.

Even though the system ad been open, the specialist shop said there was no need replace the receiver-dryer when they worked on it, but I've bought a new one this time just to be on the safe side. My plan of attack is something like:

• Examine condenser inlet fitting for sharp edges or damaged threads that could be damaging o-rings.

• Replace all o-rings in areas with signs of leakage.

• Replace receiver-dryer.

• Vacuum and recharge.

What I'm not sure about though, is the oil. Given that it was leaking enough oil to run down a pipe and form drips, I'm assuming that I've lost a fair bit. According to Alldata, there's supposed to be 200cc total in the system, and 20cc should be added for each replaced component. That's easy enough, but how much should I add to make up for the leak? Or am I going to need to flush the whole system, drain the compressor, and start from scratch? I get the impression that it's better to add a little bit too much rather than not enough, but having not worked with AC before I don't have any 'feel' for how much that should be. I'd rather avoid flushing if I can help it, since the dashboard plastics are VERY fragile and if I disassemble the dash to remove the evaporator, it'll likely fall apart even more.

Additionally, while I gather that pressure-testing with air is generally a no-no due to it introducing moisture, if I'm going to be replacing the receiver-dryer anyway, would it hurt to pressure-test with (filtered, dried and oil-free) air *before* changing out the receiver-dryer? Buying a whole nitrogen cylinder would be a big expense for something that's hopefully a one-off job, and I figure that vacuuming it for a few hours on a hot day should deal with any moisture introduced by the air. Is there something I'm missing that would make this a bad idea? Seems like, given the system's recent history, it's already had plenty of moisture exposure and a bit more air shouldn't harm it any more than it already has been, but with how hard it is to find parts for this car, I don't want to end up wrecking something unnecessarily.

Thanks a bunch!

Richard

Your plan is a good one. And yes the r/d needs changing.
Why the first shop would remove the service adapters is beyond me. If the prior owner did not affix a tag that stated it was converted that might have scared them off, but in any event their service was clearly a rip off. Smart to not go back.

Frankly messing around with dry air or nitrogen is archaic.
As I have stated many times here, in our shop we puff up the system to about 20 psi of 134 (introducing into both hi and low sides) and using an electronic sniffer. Far more scientific. The prices for sniffers has come down a lot. If you want to be serious about any kind of AC work, this is the way to go. If you are already this deep into DIY, you will be doing AC work again down the line. This method of sniffing is allowed.

When replacing O-rings be sure they are lubed with Nylog blue which you can get on-line. This will lube them and help prevent leaks.
Be sure there are no burrs on the fittings. Be sure the O-ring is the correct size.

You could totally take everything apart and flush, but I would probably just add 1 oz of the correct oil. Remember these are fluid oz.

halkyardo wrote: ↑Thu Aug 08, 2024 12:41 pm After that disaster, I made an appointment at an AC specialist, who replaced a torn o-ring on the condenser inlet fitting, recharged the system, and gave it a clean bill of health. However, within a year, it had leaked down again, with oil drips coming from the same fitting, and at this point there's no measurable pressure left in the system.

Since the condenser "fitting" leaked twice already, it could be a difficult-to-detect crack in the condenser itself. If unsure, I would simply replace it again.

halkyardo wrote: ↑Thu Aug 08, 2024 12:41 pm What I'm not sure about though, is the oil. Given that it was leaking enough oil to run down a pipe and form drips, I'm assuming that I've lost a fair bit. According to Alldata, there's supposed to be 200cc total in the system, and 20cc should be added for each replaced component. That's easy enough, but how much should I add to make up for the leak? Or am I going to need to flush the whole system, drain the compressor, and start from scratch? I get the impression that it's better to add a little bit too much rather than not enough, but having not worked with AC before I don't have any 'feel' for how much that should be. I'd rather avoid flushing if I can help it, since the dashboard plastics are VERY fragile and if I disassemble the dash to remove the evaporator, it'll likely fall apart even more.

At this point, it's pure guesswork as to how much oil remains in the system. Maybe you lost less than one ounce, maybe you lost half of it, or maybe you lost the majority of it. There's no dipstick to check the amount, so no one knows for certain how much leaked out.

You could take a chance and add "X" amount, but again, it's guesswork. If you short-change the amount needed, your compressor won't last very long, and you'll have to repeat the job again anyway, along with the expense. If you add too much oil, cooling will be compromised.

The best way to proceed, IMHO, is to solvent-flush the system (compressor excepted) to achieve a "dry" system. Although not the best option, you can flush the evaporator in situ without the tricky and time consuming job of removing it as long as you remove the TXV first. Ensure that the evaporator is thoroughly dried of any solvent. Then add 200 cc of PAG oil (6.75 fluid ounces) using the oil balancing method explained elsewhere in this Forum, or add the full 200 cc into the empty compressor, if it will take it all.

As for leak-testing the system, first verify whether it holds a vacuum. If it does, add a few ounces of refrigerant into the vacuum to achieve about 20 PSI of positive pressure, then go over it with an electronic "sniffer" as mentioned earlier. This method will avoid introducing even more moisture into the system.

The original specifications for your car are as follows: 53 ounces net weight of R-12, and 6.75 fluid ounces of mineral oil.

Thanks so much for the advice! It turns out that it's possible to get the expansion valve out from the engine bay without touching the dash, so flushing the evaporator in-place should hopefully be an option. It's good to know that leak-testing with a sniffer is OK - I hadn't quite realized how sensitive (and affordable!) they were; that approach makes sense to me.

Just waiting on a receiver-dryer to come from Europe, then I'm excited to get it all done! Will report back then.

Thanks again,
Richard

It's important to replace the R/D each time you open the system to the atmosphere. Not sure why the shop said not to. Also, install the new R/D last to minimize moisture absorption into the desiccant.

Good that you can remove the TXV from the engine compartment side of the firewall. That should make the job of flushing the evaporator much easier.