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Converting aircon on 1993 XJ from R12 to R134a

I would strongly recommend looking into an R152a conversion rather than R134a. Its pressures and refrigerant performance are more in line with R12 systems than R134a is, R134a typically needs a much larger condenser to perform as well. It's a well known conversion and I learned how to do it from an hvac nerd friend of mine.

Details...
When you convert you MUST flush all the old oil out (start by dumping it out of each component, then dump in some acetone, plug the ports, slosh it around a lot, dump it out, then flush with acetone) and put in the appropriate kind to use with the refrigerant you choose, whatever refrigerant it is. Each refrigerant is miscible with only certain kinds of oils just like oil and water will not mix.

R12 systems use mineral oil lubricant.
R134a systems use PAG (polyalkylene-glycol) oil. There are several different ones - PAG 46, 100, and 150. The numbers specify the viscosity measured in centistokes. Use the viscosity recommended by the compressor manufacturer for your model compressor.
R152a systems use POE (polyol ester) oil. I believe there are several viscosities of this as well.

None of these are particularly compatible with each other, except ester oil, which will mix reasonably well with any remaining PAG or mineral oil in the system and keep it from gumming things up.

(see http://www.underhoodservice.com/ac-compressor-oils-types-uses-differences/)

Next up... how much oil and refrigerant to put in?
I would recommend putting the same number of ounces of oil in as the system was originally designed to use. Just use the new type to match the new refrigerant.
For refrigerant it is a little more complicated. You want to use the same number of moles of refrigerant, not the same mass. A mole is a certain number (6.022x10^23 for those of you who are curious) of molecules. For any given chemical, there will be a defined "molar mass" which is the weight of that many molecules. So, you look at the sticker under the hood to determine how many kilograms or pounds* of refrigerant was originally specified, look up the molar mass of that refrigerant, divide weight by molar mass, then look up the molar mass of the new refrigerant and multiply by that. Now you have the number of pounds or kilograms of the new refrigerant to use.

* since you are going to find molar masses all in grams (all chemists use the metric system...) and you are dividing by a number of grams and then multiplying by another number of grams there's no real problem with whether you start with kilos or pounds, whatever you start with, you will end with. Use whatever you are most comfortable with.

Now, the best part? R152a is 1,1-difluoroethane. If you look at the cans of "canned air" on the shelf at harbor freight... guess what's in em? 1,1-difluoroethane. With a little bitterant added to keep people from huffing it. My wife's 1993 Buick Roadmaster currently has an AC system full of Harbor Freight canned air, and it works just as well as it did when it left the factory.

If you choose to run canned air in your system... I'm sure it'll be fine, no one has ever posted up about it causing an issue, but be warned, I am not a refrigerant expert (just a fairly well read amateur) and am not responsible for it if you do this and your AC system gets you divorced, makes your dog die, and drinks all the beer in your fridge. Make your own choice. It has worked quite well for me and everyone else I know who has done it.

Also, I have all the tools (vac pump, gauge set, UV light, can taps, etc etc) to do this... I'm not fixing leaks in your system, but if you buy the beer+refrigerant/canned air and are near central mass, bring your jeep with a flushed AC system and I'll fill it. Open offer.
 
The Low Side port is the important one since that is the port used to fill the system. This adapter should solve the problem for you. This adapter bolts directly onto your compressor and then provides an output port for connection to the hose. It simply inserts the R-134 access port on top. I had a set of these on a different project and they will do the job.

HTH
Todd

http://www.partdeal.com/sanden-selt...MI9Lz1562Q2gIVxuDICh3zGwW2EAkYCSABEgKSgvD_BwE




Todd, as with your previous posts, that latest info is hugely helpful.

Just to set your mind at rest on one point - my Jeep is a stock US-spec, LHD vehicle. Long story short, I bought it new as an 'import' in 1993 (from a Belgian agent who I guess mainly supplied US Forces personnel in Europe) because I needed an LHD to take out to my work in the Middle East and the Jeep dealers in UK couldn't, or weren't allowed to, sell LHD models. Brought it back to UK a decade later, and have continued using it ever since. So that's why I'm reliant on Rock Auto and US suppliers for anything beyond routine replacement parts, and hang out on NAXJA forums rather than any UK online networks.

Thanks also for that brilliant, simple, straightforward guide to hoses and their descriptions. I reckon I'm just about there. All the new hoses seem to have the standard connectors at each end so no special tools needed. The only new hose I haven't got is the hard-to-find drier-to-expansion-valve one. I think I'll just have to re-use the original. I have a new discharge hose with the T-valve for the high pressure connector, but unfortunately the new suction hose I have doesn't have the T-connection for the low pressure connection. Hope my engineer friend can figure out a solution to that.

To correct a small error in my previous post: the compressor does have a drain plug and I have drained what oil remained. I will indeed re-use that compressor. Also noted the drier connections and switch, and will be replacing all the seals I can find!

My Easter weekend schedule is now clear: long hours in the garage.... Well, it's all part of life as an XJ owner!
 
The only new hose I haven't got is the hard-to-find drier-to-expansion-valve one. I think I'll just have to re-use the original. I have a new discharge hose with the T-valve for the high pressure connector, but unfortunately the new suction hose I have doesn't have the T-connection for the low pressure connection. Hope my engineer friend can figure out a solution to that.

About two years ago one of the original lines on my '92 rotted out from age (was one of the liquid lines, possibly what Todd described as #3 above). My mechanic was able to source one, but I had posted up here looking for ideas on where to find it because I hadn't been having any luck myself and if memory serves, someone suggested taking the line to a place that makes hydraulic lines and have them duplicated it.

Obviously I ended up not needing to do that, but your truck is nearly as old as mine, depending on what they use to keep snow/ice off the roads in your part of the world yours may not be in great shape either. Even if they are, if all the other lines are new, any you reuse could be weak links in the system.
 
Well, the saga continues. My engineer friend and I spent this afternoon on the task. Progress on most things, one or two glitches, and a couple of queries (which may link into some of the most recent posts by others....).

Let me however first thank kastein for both the scientific briefing and the help offer. Just a few points. There really isn't much choice over here in UK of alternative refrigerants (forget propane... and I don't think R152a is available.... and as for "canned air", no chance). So whatever the theoretical merits or performance advantages of other chemicals, R134a is what I have to go for. And while a beer always helps, Central Mass is a bit far from the Highlands of Scotland, so I can't exactly pop over to seek a helping hand!

It's late night now, but I'll try to post up a pic or two of the backside of my compressor for eHall to look at.... It's a Sanden 7701, with those three-position valve-control things and no schrader valves. We've drained, flushed and re-mounted it, but not connected any hoses to it, and the expansion valve block is not reinstalled yet,

Today's work was essentially flushing the evaporator, removing and cleaning the expansion valve (the block was a pig to remove), and draining and flushing the compressor. I have new rcvr/drier, new condenser, and three new hoses. Three issues have surfaced on which any comments and help will be welcome:

1) strange fitting in the end of the liquid line (drier to expansion valve/evaporator - the one which I have to re-use as I have no new replacement). At the end where it connects to the drier, there seems to be some kind of valve fitting. All we can see is a little 'button' in the end of the hose (but I have seen a YouTube video which suggests that there is a little spring-loaded valve-thing inside). My engineer recalls seeing one in the a/c system on a classic Bentley many years ago. He thinks it's only for R12, and that it's not needed for R134a. We haven't yet looked at whether or how this would connect to the new drier. Should we just do without it? I'll take a pic if I can...

2) home-made liquid line? This pesky hard-to-find line is of course 25 years old, so could be a bit tired anyway. Depending on what the purpose of that weird little valve thing is, my friend is talking about making up a new hose from the fittings and spare hose he happens to have in his workshop.

3) No R134a T-valve connectors. I had a choice of two new high pressure discharge hoses (compressor to condenser), a 4 Seasons one with no T-valve, and a UAC one with an R134a T-valve. Turns out only the 4 Seasons one is the right shape to fit. The UAC one lacks the right-angle bend needed to line up with the compressor connection. So we will have to fit the one with no T-valve. The new suction hose I have (low pressure, expansion valve to compressor) has no R134a T-connection) . So we appear to have no choice but to fit R134a adapters on to the back of the compressor and use them for gauges and filling. Such adapters aren't available at your local auto parts store in UK, so my engineer friend is rummaging through his stock of bits, and if he can't help then I'l have to get them online.... Probably something like the item that Todd linked to in his recent post?

More work in prospect tomorrow. Will post pics if I can. Meanwhile, any comments still welcome!
 
Now here we go with pics - I hope.

First, these are pics of my original liquid line (removed from the vehicle) with close-ups showing the strange valve-button thing in one end of it ....

IMG_6153.jpg



IMG_6155.jpg



IMG_6157.jpg




and also pic of the old receiver/drier showing where this connected.


IMG_6168.jpg




So the question is, what is it, and is it needed for R134a systems?
 
I haven't figured out how to post up links to the photos (which are on Photobucket) so that they show up a bit smaller. So here, for eHall, is just one view of the rear of my Jeep's compressor. The ports have been taped up as the hoses haven't yet been connected.

IMG_6167.jpg
 
Okay, an alternative way of showing photos. I have uploaded a selection of pics of my Jeep system into a Photobucket album.

We are part way through the conversion, so most hoses are disconnected, and the expansion block removed. The new condenser is in place (in front of new radiator) with its two lines connected. The compressor is remounted but not connected, and the new drier is in place but also not connected.

The collection of pics - with brief titles - should be viewable here .

Let me know if these links don't work, or if there is a better way of showing photos.
 
Good job so far! A couple of quick comments:


1) I don't recall seeing that valve device on my system but it was a while ago. My instincts say that if the new drier has a similar valve internal to the opening, you should probably leave it on. If not, go with the straight hose.

2) I actually removed both of those R12 valves from the rear of my compressor and plugged my hoses directly onto the compressor. The threads should be the same so you can reduce the parts load a bit by tying your High Pressure line directly into the compressor and perhaps leave the low line connector on as a means to charge the beast up? I'm assuming your engineer friend has a set of manifold connectors for R12 and if so, maybe he could use the R12 low line connection for charging and use the R134 high pressure line just for the measurement (?)
 
Good job so far! A couple of quick comments:


1) I don't recall seeing that valve device on my system but it was a while ago. My instincts say that if the new drier has a similar valve internal to the opening, you should probably leave it on. If not, go with the straight hose.

2) I actually removed both of those R12 valves from the rear of my compressor and plugged my hoses directly onto the compressor. The threads should be the same so you can reduce the parts load a bit by tying your High Pressure line directly into the compressor and perhaps leave the low line connector on as a means to charge the beast up? I'm assuming your engineer friend has a set of manifold connectors for R12 and if so, maybe he could use the R12 low line connection for charging and use the R134 high pressure line just for the measurement (?)


Thanks. The new drier doesn't seem to have that valve type fitting where the hose connects to it.

By the R12 valves I assume you mean that whole assemblies - the two (brass?) blocks with those control-taps and the hose ports at right angles to the back of the compressor?

We talked about that. The two problems are (a) they'd be very hard to remove: brass and aluminium probably almost bonded together? and (b) the alignment of those fittings puts the ports at right angles to the compressor. So they line up with the (old and new) hose connections, which are bent so that they are in the right position. So these hoses wouldn't line up if they had to connect straight into the back of the compressor. We may have to experiment with different adaptors to see whether anything will fit and what kind of connectors could be fitted, and where, to enable filling and measurement.

More reports in due course!
 
More details (as it's now daytime in UK and I'm back on the case). Beginning to feel like Sherlock Holmes.

Trying to figure out exactly what the strange in-line valve thingy is which we found in the liquid line that runs from expansion-valve block to receiver/drier. I posted photos up on Photobucket - hope others can see them as PB seems to want to insist that I buy a paid subscription. Will have to look at alternatives....

Anyhow, I found a couple of comments from Ecomike and JoshInReno in another thread on the forum here . Much of that discussion is about aircon on a Renix vehicle, but as it was about the R12/R134a conversion much of it seems relevant. Posts #7 and #10 suggest that the in-line valve thingy is superfluous and unnecessary.... so we may end up trying to remove it when we reassemble my system.

The struggle continues!
 
Yet more to report. We have flushed and reassembled the system. Tomorrow, leak testing, vacuum, and (I hope) fill with R134a.

But one gremlin lurks. My previous posts raised the query about the curious little valve-thingy, with a spring loaded thingy inside it, which is connected between the receiver/drier and the liquid line to the expansion valve block/evaporator. It's visible on the pics I posted of that liquid line.

I can't even find a schematic diagram online of exactly what this valve thingy is and how the internal bits work.

The advice is that it's unnecessary. The problem is that the end of the liquid line pipe has a 'male' screw thread; and the fitting on the rcvr/drier has a 'male' screw thread. So simple removal of the valve thingy isn't possible as the pipe then won't connect to the rcvr/drier. It would appear to need some kind of straight-through adapter piece , which would have to have 'female' threads of the right size/pitch at eachend.

Has anyone else grappled with this problem, and found a solution?
 
The only thing I can imagine is that the valve is an attempt to keep a leak in the condenser (the condenser is the one that gets the most abuse from road debris) from causing the entire system to remain open. Not sure it would actually do the job but I can't imagine any other reason for it being there.

Yet more to report. We have flushed and reassembled the system. Tomorrow, leak testing, vacuum, and (I hope) fill with R134a.

But one gremlin lurks. My previous posts raised the query about the curious little valve-thingy, with a spring loaded thingy inside it, which is connected between the receiver/drier and the liquid line to the expansion valve block/evaporator. It's visible on the pics I posted of that liquid line.

I can't even find a schematic diagram online of exactly what this valve thingy is and how the internal bits work.

The advice is that it's unnecessary. The problem is that the end of the liquid line pipe has a 'male' screw thread; and the fitting on the rcvr/drier has a 'male' screw thread. So simple removal of the valve thingy isn't possible as the pipe then won't connect to the rcvr/drier. It would appear to need some kind of straight-through adapter piece , which would have to have 'female' threads of the right size/pitch at eachend.

Has anyone else grappled with this problem, and found a solution?
 
Just to slip into this thread a reply to Rainman....(and others who proposed various kinds of refill gas).

Thanks but I'm simply not going down the road of looking at alternatives - exotic or otherwise - to R134a as a refrigerant. R134a and PAG oil are readily available here. Other products/combinations are not. I'm no expert on hydrocarbons and fluorocarbons of whatever formula.... but the UK is still (for the moment) in the EU, and the regulations about what is sold, how, and to whom are probably a great deal more complex and restrictive than in the US, Canada, Australia or elsewhere.

My issues are about the hardware - hoses, pipes, connectors, valves - not about the stuff that flows through them. So that's what this thread is focusing on.
 
Just want to thank you guys for this timely thread.

I am in the process right now of obtaining all the parts needed to get AC in to my little 93 Chero.
I too will be converting to 134a so this is really great stuff!
 
Singapore? That's a bit too far to drive.

EDIT: This was in response to a SPAM post about an AC shop in Singapore. Looks like it got deleted.
 
Last edited:
Eh? Not quite clear how this comment relates to the 3-page thread discussion from 2018.

There was a SPAM post prior about an AC shop in Singapore. Looks like it got deleted. I edit (if I can) the prior post).
 
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