Last year (might even be the year before) I fitted a new condenser, drier, pressure switch and tri-swich to the air con system and took it to be gassed. It held a perfect vacuum on the machine and the guy in the garage commented on how well it had done. Unfortunately it lasted 24hrs. When looking under the bonnet I could hear a hissing noise from the pipes along the bulkhead.

I've now replaced both of them and more (5 in total I think from memory), fitted a new drier again and have been contemplating taking it to be recharged. Reading in RAVE it gives you instructions to test the system to 3 bar using Nitrogen. This got me thinking...

I've got old Citroen's that use hydraulic suspension. The damping on them is controlled by nitrogen filled spheres. I've got a huge nitrogen cylinder for recharging spheres. I've also got a set of air con gauges that I bought on eBay years ago.

The threads weren't going to work on the Citroen regulator on the Nitrogen cylinder but Dad reminded me that there was an unused Argon regulator on the shelves gathering dust. I opened the box and found that the regulator fitted the Nitrogen cylinder. I had an old oxygen hose from an acetylene welding set that had perished at the end where it went into the nozzle so I cut that off, remade the connection and it fitted the Argon regulator.

I didn't have as much luck getting it onto the air con gauges, however, brute force and a jubilee clip has it gas tight!

There's 180 bar of Nitrogen in the cylinder but thankfully the regulator works in nice small numbers so it's set to 3 bar.

I then levelled the gauges off on the car and have left them sitting as close to 3 bar as I could get them.

I've now left it in the workshop connected to the gauges and I'll see if it's still reading 3 bar tomorrow night after work. If it is, I'd say it's fairly safe to get some gas put in it without it being as effective as tearing up a couple of £50 notes in a cold shower!

David.

I've recently done the F Gas for industrial and domestic and the automotive AC courses and got my qualifications for them. A couple of mates, both in the entertainment industry so have no work on at the moment, did the automotive course so they are doing mobile AC re-gassing while they have no proper work. I (illegally) installed AC in my daughters house and have since been asked to do installs for other people so did the F Gas course. F Gas is a 4 day course compared with automotive being a 1 day one so I asked if I could also do the automotive while I was at it. As this was only a few weeks ago, it's all still fresh in my mind, so RAVE is wrong. R134A runs at between 12 and 15 bar depending on ambient temperature and a pressure test should be done at 1.43 x operating pressure. However on automotive systems, 10 bar is regarded as the 'safe' pressure test, it will show up any leaks but won't cause any that weren't already there. So you connect up the Nitrogen (should be OFN really), crank it up to 10 bar and then leave it for 30 minutes. Even the smallest leak will show up almost immediately with the gauge on the bottle dropping. Then you let the OFN out and vacuum down to around 1.3 mBar (1000 microns) before refilling with refrigerant. it's this bit that the automatic machines that most places use do. So will manually pressure test with OFN before letting the machine do it's thing but most don't bother and rely on the vacuum test. It's very common for a system to be able to hold a vacuum but not pressure, so it's not a valid check really and there's no substitute for doing it properly, although that does rely on whoever is doing it knows what they are doing, and most don't......

Gauges are cheap enough these days and the Argon regulator you've got is fine for what you are doing (domestic AC systems running R410A or R32, need to be pressure tested at 37 bar so need one a bit meatier) but it's the vacuum pump that you probably don't have.

I do have a vacuum pump and an old cylinder of R134a but there's not enough left in it to do the P38 so for all it costs I'll pay to have it recharged once I'm sure it's leak free.

Strange that RAVE reckons it needs pressurising to 3 bar for pressure testing though.

David.

They are obviously being cautious as the system runs at 4-5 times that. The electronic leak detectors aren't a lot of good in all honesty. They have to be set at their most sensitive then they end up responding to any exhaust fumes, oil fumes and anything else floating around. On the course we just used the very same Fairy Liquid and water mix I use for looking for EAS leaks!

Well, we had no leaks at 3 bar over night so this evening I upped the pressure in stages to 10 bar.

I found one leak as I let the pressure hover at 6 bar. It looks like I didn’t tighten a union properly when I replaced the pipes.

After I’d nipped that I took the pressure up to 10 bar.

And thankfully, this picture was taken an hour later.

I’d say that’s ready to be gassed with R134a now.

David.

Certainly is. That leak on the pipe union would have lost your refrigerant in a matter of days, but all looks fine now, well done. The other good point is the Nitrogen will draw out any moisture or contamination when it is let out, so it'll work better once is is filled.

Who did you do your course with Richard? I'm part way doing it at the moment - was meant to have done it back in April but ye olde 2020 fun and games put the brakes on things.

He'd be a bit far away for you Nick, Tony Muxlow Developments (https://tony-muxlow-developments.co.uk/) who is an hour up the A1 for me. He does have accommodation there but I suspect that is extra (although Mrs Muxlow does appear regularly with coffee and at lunchtime a plate of sandwiches). Under normal circumstances he does training sessions at various other places but that isn't happening at the moment. The F Gas course was £995 + VAT (and F Fgas registration a further £142) and I think the Automotive one is around £300 if done on it's own but it is only a day. Biggest problem I had was that he starts at 8am meaning I had to be out of bed earlier than when I was working!

I mean - I'm literally doing it at the moment. Have just sat my exam. Practical assessment to go and it should be all done. Thankfully I'm not paying for it, but it will benefit me both at work and personally.

I did the practical on my car. It was a choice between doing it on a test rig in the classroom or the other side of a door in the car park. Full recovery, pressure test, vac and refill and I know for definite I've got the correct amount of gas in it.

No point doing a practical on mine at the moment - more than half of it is missing :) The precious magic sauce is currently stored safely away to go back in once I've made some pipework up.

What’s the script with oil in the system? Last time mine was gassed they put oil in it but it leaked the gas. Should they be putting more oil in it this time too?

Vac won't draw the oil out, only air, and when the gas leaks you might get a tiny bit of oil come out with it but it will only be a very small proportion of what is in there. So what is in there will stay there unless it has been drained out. Your system takes 180 ml so maybe they could put 20-30 ml in just to be sure (unless you fancy taking the compressor off and draining it all out).

Hmm, I think my compressor bearings might be ever so slightly noisy. I wonder if I can get a replacement before Tuesday and then it's all done in one go. It's probably not worth it as I'm likely being waaaay to picky but it's nice to have it right.

If you replace it then make sure the oil is in it when you put it on. Was over at my mates yesterday working on a P38 and he'd got a couple of customers booked in to have their AC re-gassed at his house rather than mobile. First one wasn't a problem but the second one passed the pressure test no problem but still wouldn't cool as the compressor clutch wasn't engaging. Turned out that the compressor was seized solid and I suspect the thermal cut-out had done it's job and cut the power. Owner then admitted it had last been gassed about 2 years ago and at that time had needed a new compressor. Recovered the gas, took one of the pipes off and it was completely dry inside suggesting whoever had replaced the compressor hadn't put any oil in it hence it had seized.

Having spent a few days this week pulling apart my fridge freezer - and reading a comment that F/F systems don't leak like cars do as the compressor is electric/ enclosed and so has no leaking bearing seal (where mine leaks)...I got to wondering why cars don't use an electric compressor, instead of the mechanical/ rotating one...
Richard/ Sloth this one will be right up your alley !!

Because of the amount of current they'd draw. It isn't noticeable on a P38 because even at idle there's plenty of torque available to turn the compressor and the ECU is given a signal from the HEVAC to open the IACV to keep the revs stable when it engages (stick the Nano on and look at the idle air valve opening and watch what happens when the compressor engages). On my daughter's 1.8 litre Toyota Celica, you can hear the revs drop when it engages and she only uses it when she really has to as the fuel gauge plummets too.

No doubt someone will come up with an electric compressor sooner or later just like quite a number of cars now have electric power steering. The modern DC Inverter, heat pump domestic systems are very efficient, giving 3kW of heating or cooling for 600-700W of electrical input so it wouldn't surprise me if someone starts putting a similar system (the components are the same, compressor, condenser, evaporator, refrigerant it's just the electronic control that is different) in a car. Could do away with the conventional heater running off the cars cooling system too. So you'd be buggered trying to find heater hoses to plumb an LPG system into.......

Electric cars already do - given they have no combustion engine to drive one otherwise. But then they also have high voltage available - which is really what makes it possible. At 12v you'd need potentially over 100 amps to drive an electric compressor of a suitable size to get the cooling capacity required. So consider a) the additional alternator capacity and b) the size of the wiring to support it, and it's not worth the complication.

On most modern normal cars the compressor runs all the time now, and can adjust its own capacity, adjusting discretely - so you don't get that tell tale drop in revs or audible clunk of the clutch pulling in/letting out when the controller calls for more cooling. I say most - I know it's true of 'higher' end marques. Like inverter driven electric compressors almost. Pretty cool.

Sloth wrote:

On most modern normal cars the compressor runs all the time now

and, unfortunately, last no more than about 5 years......

The R12 system in my Shadow gets so cold frost appears on the airvents lol

They did it better in the old days ;)