DIY Aircon top up.

norseman said:

the print-out shows 230g recovered

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Could that possibly be, at least partly, water ?If you have lost gas, this will be replaced by air, and I believe one of the advantages of specialist top-ups are filtering the gas to remove impurities.

Do we have anyone on here that does this for a living?
It would be interesting to know if the supposed universal gas top ups (natural hydrocarbon?) can be mixed with R1234yf ?

mattylad said:

If your car was produced after 2013 then it's more likely that it needs the newer and more expensive gas, the top up canister is £130 at Halfords.

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mattylad said:

Do we have anyone on here that does this for a living?
It would be interesting to know if the supposed universal gas top ups (natural hydrocarbon?) can be mixed with R1234yf ?

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You got me looking at that. Apparently, cars produced after 1st Jan 2017 must have the RF1234 gas by law.
I thought I’d be able to top up our A3 if it needed it. I had a look yesterday and that’s what our A3 has. The gas I got for the Golf was the R134A gas. From what I’ve read, they can’t be mixed. You also need a different type of connector for those cars too. Bugger!

I had mine drained, pressure tested and refilled, just to make sure it was fine around three years ago by a mobile guy for £50, with the proper equipment. I was aware the condenser was on it's way out, not working as well as it could, the fins rotting from the salt. Obvious really, the cooling fan was running high speed far too often, when the a/c had demand. Last year, it suddenly failed completely - almost certainly time for a new condenser to be fitted, so I got the same guy to give me a quote. He offered an OEM or a cheaper copy condenser, I had him get the OEM one and fit it. That cost me around £250, all in. The old one was just a pile of alloy dust, with an obvious oily mark where it had leaked.

mointainwalker said:

Could that possibly be, at least partly, water ?If you have lost gas, this will be replaced by air, and I believe one of the advantages of specialist top-ups are filtering the gas to remove impurities.

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The lost gas won't be replaced by air if there's positive pressure in the system. It will be like a partly-used aerosol can. There will be less "stuff" in it, but no air. It is absolutely normal for car aircon systems to lose gas slowly, over time.

Mottie said:

You got me looking at that. Apparently, cars produced after 1st Jan 2017 must have the RF1234 gas by law.
I thought I’d be able to top up our A3 if it needed it. I had a look yesterday and that’s what our A3 has. The gas I got for the Golf was the R134A gas. From what I’ve read, they can’t be mixed. You also need a different type of connector for those cars too. Bugger!

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They are absolutely NOT compatible!!! I noticed Halfords were doing 1234YF top-up kits just like the 134a top-up kits, but they're bloody expensive! There's been a long battle raging over 1234YF. The problem with aircon refrigerants, is that they're vicious greenhouse gasses. The EU has been restricting the "GWP" (Global Warming Potential" of car aircon refrigerants for some years now, and the most recent Directive specified a GWP of less than (can't remember - 150, I think). The only commercially-available refrigerant that would meet that requirement was 1234YF and Honeywell / DuPont (now merged as Chemours) held the patent. They had the car industry by the short & curlies and that's why it's so bloody expensive! The car industry, (notably Mercedes) pushed back against this in various ways, but it was mostly bullshit. In the end, they just had to bend over and take it.

norseman said:

I've though above this action myself, but if the system is re-gassed at a garage some of the gas is recovered so is the DIY approach as efficient?
Our 23yr. old 5 series has just been done & the print-out shows 230g recovered & 760g injected.
Is there a difference in price between the two gases ie pre'97 (ish) & the later R134a ?

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Yes, the "proper" method, involves emptying all the refrigerant out and putting a vacuum on the system. This (a) boils off any water in the system so that it turns to vapour and is extracted with the old gas and (b) checks the system for leaks (it has to hold a vacuum for a set amount of time). The DIY top-up method obviously doesn't do that, it just adds more refrigerant (plus a random amount of lubricating oil, and sometimes, various "magic chemicals" that are supposed to "condition" seals (whatever that is!) and stop leaks. Technically, you should also change the receiver / filter / dryer assembly too, but few people do that in a re-gas - even proper dealers. Water is death to an aircon system!

What I don't like about the top-up cans, is that some of the cheaper ones don't actually have 134a in them. They are "134a compatible". No idea what's in them. I think butane is quite popular, but of course, that's highly flammable! Also, the gauges are pretty suspect, being a "one-size fits all" solution. Aircon systems operate at slightly different pressures depending on the car, and these gauges only ever monitor pressure in the "low side". Their primary purpose is to "sell refrigerant top-up" so it's quite easy to over-fill your car and put more strain on the compressor and belt, for less cooling effect (because there isn't the volume left in the system for its to expand and cool properly). On occasions when I have been to a "proper" place for a top-up, I've put the DIY gauge on as soon as I'd got home, to find that it is barely on the bottom edge of the "green" zone, yet, I have to assume that's the correct amount of refrigerant. In fact, I added a bit more from a top-up can once and there was a bit of belt squeal, so I reckoned that the garage machine probably had done it right.

The last grouse I have, is the magic "seal conditioning" chemicals. I think they just attack your seals and cause them to swell up, thereby plugging leaks in the short term, but actually turning your seals to jelly in the long term. However, I have no concrete evidence of this, it's just a hunch!

Thank you Avocet for such a detailed answer, very informative.
Despite running my AC on a regular basis, ie on at least part of each journey, it's needed a re-gas at the start of each summer as after 12 months or so the AC is cooler than the car's ventilation system, but not what you'd call really cold. The procedure has been carried out at two different outlets, both using Sun equipment, with the car's system holding vacuum each time. I wonder if such a regular re-gas is par for the course, perhaps due to the age of the car ?

Avocet said:

On occasions when I have been to a "proper" place for a top-up, I've put the DIY gauge on as soon as I'd got home, to find that it is barely on the bottom edge of the "green" zone, yet, I have to assume that's the correct amount of refrigerant.

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I did wonder about that. When I put my gauge on it was showing low pressure. I topped it up and when I checked it was just in the green zone and the instructions said to fill until vent was blowing cold and to not overfill. I was tempted but is was back blowing cold and I thought I can always add more if needed.

The last time I got a top up it was the older gas and it cost me £30 at an AA garage.

This time its looking like £150+

mattylad said:

The last time I got a top up it was the older gas and it cost me £30 at an AA garage.

This time its looking like £150+

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Is your car on 1234YF? IF so, I'm surprised it already needs a top up. If it's 134a, that looks like rather a rip-off price to me.

norseman said:

Thank you Avocet for such a detailed answer, very informative.
Despite running my AC on a regular basis, ie on at least part of each journey, it's needed a re-gas at the start of each summer as after 12 months or so the AC is cooler than the car's ventilation system, but not what you'd call really cold. The procedure has been carried out at two different outlets, both using Sun equipment, with the car's system holding vacuum each time. I wonder if such a regular re-gas is par for the course, perhaps due to the age of the car ?

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If it won't hold its charge for a year, I think there's a problem. Vacuum testing isn't the best way to test, but it's quick and easy. To be honest, I'm a little sceptical of the automatic machines that the likes of KwikFit use. Obviously, they're geared towards (a) selling top-ups and (b) doing the job quickly. I had my Landy topped-up by KwiKFit last year and they said it held a vacuum just fine, but by the start of the warm weather this year, it needed re-gassing.

Avocet said:

If it won't hold its charge for a year, I think there's a problem. Vacuum testing isn't the best way to test, but it's quick and easy. To be honest, I'm a little sceptical of the automatic machines that the likes of KwikFit use. Obviously, they're geared towards (a) selling top-ups and (b) doing the job quickly. I had my Landy topped-up by KwiKFit last year and they said it held a vacuum just fine, but by the start of the warm weather this year, it needed re-gassing.

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Thanks for the reply, in point of fact neither re-gas was carried out at KF or similar outlet, but at two different garages both using Sun equipment, one of which was our local workshop. Perhaps when it needs another 'gas next year I will get the system properly checked out by a AC specialist.

The trouble with car aircon is that, even with a good system, it will very slowly leak. The reason for this is because, unlike a fridge, it is not hermetically sealed, it has crimped rubber hoses with quick connect fittings for production line assembly and it has a compressor shaft seal. The best way of keeping it from slowly leaking is to use it.....lots. The PAG oil that is dissolved within the refrigerant gradually condenses and sinks to the lowest part of the system but the best place for it is on the O rings and the compressor seal and it will only stay there if it is used often, even in winter.
Also caution is required not to overfill as it is filled by weight and not pressure, so if you are topping up, you only put enough in for it to go cold.....more is NOT better!

Bodgedbuild said:

The trouble with car aircon is that, even with a good system, it will very slowly leak. The reason for this is because, unlike a fridge, it is not hermetically sealed, it has crimped rubber hoses with quick connect fittings for production line assembly and it has a compressor shaft seal. The best way of keeping it from slowly leaking is to use it.....lots. The PAG oil that is dissolved within the refrigerant gradually condenses and sinks to the lowest part of the system but the best place for it is on the O rings and the compressor seal and it will only stay there if it is used often, even in winter.
Also caution is required not to overfill as it is filled by weight and not pressure, so if you are topping up, you only put enough in for it to go cold.....more is NOT better!

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That last bit is especially important. The system pressure (when switched off) varies a lot with ambient temperature, so it's impossible to determine how much is in the system using a pressure gauge. Because the system works by pressurising a gas into a liquid and then allowing it to expand back into a gas again, if the system is over-filled, there's less volume for the liquid to expand back into a gas again, so you don't get the cooling effect. Similarly, the lost gas, as you say, permeates the flexible hoses and other seals, but the lubricating oil tends to stay in there. SOME, however, will be lost. When the system is properly evacuated before refilling, it's easier to estimate how much oil needs to go back in. With the top-up cans, you just end up adding "some", but you're never really sure how much was lost in the first place, or whether the can had the right amount in it for your car anyway...