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AC repair and recharge questions


Ok, this post is full of bad ideas so go ahead and shout at me if you need to.

I have a 1985 BMW 318i, 5 speed manual.

So, I had this crazy idea that since it’s pretty much been 100 degrees every day since April I need some AC in this car.

Now, some background info. I have no idea how long this car sat or how long it had been since the AC was last serviced. I have been very successful DIYing everything from timing belts to half shafts to… pretty much anything but a transmission issue, but I decided one must learn somewhere.

Some more background info, in order to retrofit this vehicle it is recommended that you replace the compressor as the original equipment model is not 134a compatible, but I have it on good authority that dumping a little in will get you some cool air but burn out the compressor more quickly and you should not mix the oils.

Ok, so, with this in mind and the idea that this would be the last summer I’d be driving this car, I went ahead and simply purchased an adapter for the low side valve and some 134a. I know this is not a proper retrofit, but I found that the car held no pressure, and I simply don’t care if the compressor burns out after a week, because that’s about how long I need the AC to run anyway. Longer story, won’t go into it. Anyway, before charging I looked for obvious signs of damage and leaks, cleaned the condensor and checked to see if the clutch would engage and if the condensor fan was running. I came up good on all counts.

So, I decided there wasn’t much else to do but to start adding my 18 oz can of charge and see what happens. So, I began charging. The low side pressure started to rise and got as high as about 25 psi and then dropped back to zero, the compressor had kicked on, so I guessed that was a good sign. I added the rest of the can and the pressure never came off zero. I read that these cars had required about 2 pounds of R12, so I figured I’d start another can and see what happens. I began adding the second can and the pressure began to come off zero psi finally. I got it up to about 10 and decided to feel at the vents. It was barely there, but it started cooling down just ever ever so slightly. So, I squeezed in a little more, checking the gauge I was at about 11 or 12 psi on the low side. I began to add more, and that is when things went terribly wrong.

I heard a loud pop and suddenly found myself in a white cloud. I released the trigger on the can. Stepping back I watched the low side gauge climb to just at redline very rapidly. I stepped back fearing and explosion and shut the car down. I gave things a minute to settle and with the gauge on the low side still at red line I removed the hose from the low side fitting. I could still hear gas escaping, and I located the leak. The rubber line that runs between the low side line and compressor had been resting on one of the rails of the car and had simply worn through. I missed this on my initial inspection. Once the line came up to pressure, it blew through completely, but it is absolutely plainly obvious that the leak was due to this line of wear from contact with metal.

So, I have two questions oh wise ones.

  1. How the hell do I remove this line at the low pressure line? It seems like I just unbolt from the compressor, but the other end? Any ideas? Seems like it should be easy, but I’m not so sure.

  2. I have access to proper R12 now, but given the spike in pressure on the gauge, did something else happen as well, or is that just a result of a leak on the low pressure line? Given this scenario, is that pressure reading “normal”? If so, aside from replacing the line and pulling a vacuum is there any other step I should take to start riding cool?

Thanks for your help, as this community as helped me so many times.

Also, no need to remind me that I should have the system evacuated before removing the hose now. Pretty sure it already took care of that itself.

First, you replace the ruptured hose AND the receiver/dryer. THEN you have a professional repair shop evacuate and recharge your system, adding the proper amount of PAG oil or whatever they use when doing conversions…OR you will continue to waste your money on failed attempts to get the system operating again and risk a nasty injury which you just narrowly escaped…

I’ll switch out the receiver dryer, the hose will simply have to be patched. I can’t find anywhere to get it, and the places that have quotes for it are prohibitively expensive. I’m fairly well assured that the patch will be… acceptable, if not the optimal or most preferable solution.

I am contemplating taking it to a shop, however this will no longer be a retrofit, it will be charged with the original R12.

Additionally, please don’t take quite that tone. I’m very careful and wear recommended protective equipment when I do these repairs, and I do take them seriously. The point is I’m not concerned with fouling the compressor. The money you claim I’m wasting is no waste, for 20 bucks I found my leak, wich was kind of the idea in the first place. As for overhauling the system, I’d have to do that for a proper retrofit anyway which isn’t really the plan anyway.

The proposition, in short, is that it gets fixed cheap and quick, or not at all.

What I’m looking for is any recommendation based on what I observed as to whether or not there are other specific parts of the system that need to be checked. Since I will be recharging with R12 and not doing the retrofit, changing oil, etc. I may take it to the shop for a proper dose of R12.

Bottom line is this:

I don’t mind dumping two cans of R12 in it at $20 a can. I also don’t mind fixing a line and replacing a receiver/dryer to make that happen or taking it to a shop afterwards to have it vacuumed.

What I do mind is replacing other larger parts of the system that will be expensive, difficult to obtain (if possible to obtain at all), and difficult to replace. If that is the case, I’m going to go without AC. Simple as that. It simply isn’t worth the effort.

Again, if anyone has advice on other parts I may need to check, I’m all ears and thank you in advance.

What should be done after the line is repaired is to pull a vacuum on it and allow it to sit for quite a while. If there’s any leak at all anywhere there will be a noticeable drop in the vacuum.
This saves refrigerant and wasted time charging a system just to have to empty it all out again to repair a leak.

With age and non-use I would be very surprised if the compressor shaft seal does not leak.

For what it’s worth, R-134 will cool just fine and will not shorten the compressor life assuming the compressor is actually good, the proper oil used, there are no other underlying problems, and so on.

Yeah, I think more and more I’m planning on having the vacuum done after the line is repaired. I’m not sure, but it doesn’t seem to have any other catostrophic leaks in there, but who can be sure. It was holding steady at 10 psi for a bit before I added more, but I know that’s just the low side. In any event, it makes sense that the vacuum would detect other leaks.

Will the vacuum detect other possible problems though? I’m trying to avoid charging it and then having it evacuated again to repair some other bit. I know I don’t have much to work on in terms of operating diagnosis, but are there any other clues there?

I’m not opposed to running the R-134 but if you do some research on this particular car, to do a retrofit you are flat out told to replace the compressor. I understand in theory how the compressors work, but I’m no expert and I don’t know how they are designed, however I’ve been told this is a 5 stage compressor while most vehicles carry the 7 stage variety which is what is required to use the R-134. Again, I’m reasonably assured that it will work at least for some time, but not how well or that the compressor will last under this circumstance. Which, again, would have been fine as long as I could get a month or two out of it.

Incidentally, working from the general idea of what I put into the system and that it sat for a good 24 before I added anything else I have a general idea that nothing leaked out of the first 18 oz I put in durring that 24 hours, or if it did it was a negligible amount.

The thing that still bothers me is that spike in pressure on the gauge. Especially since the leak is right in line with the low pressure line. Why the heck would a leak in the low pressure line cause the psi to go up?

Drats. The information I gave before was incorrect. My leak is located on the high pressure side of the system, not the low pressure side as previously stated. Just took another look. Sorry for the confusion.

Those DIY chargers are labelled to indicate low side running pressure. When the compressor is not operating a fully charged system will have equal pressure on the low and high side and it would be in excess of 90 psi in 100 ambient temperature. While operating properly the low side should be between 30 and 40 psi and 240 to 300 psi on the high side. A set of gauges is highly advisable, Although I don’t recommend doing so I have seen several AC systems given the “down and dirty” retrofit to R134 and operate for over a year. A full vacuum is absolutely necessary though.

You’ll be happy to know I’ve lucked out on a set of proper gauges for $30 that someone no longer needed.

I’ve been sold on the vacuum, and that’s pretty much the same that I’ve heard on the down and dirty retrofit, which is about as long as I want it to work. So that’s good.

I’ve got another issue though. The hose I have the leak in is on the high side, and I can’t locate a replacement.

I know the pressure is high… I’m thinking clean it up, fill in the gouge with glue, rubber patch possibly a slit hose to fit over the existing one with more glue, some hose clamps, and half a roll of duct tape = joy?

Just keep in mind this isn’t a spry youngster of a vehicle. Parts are difficult to locate and this doesn’t have to be a pretty perfect forever repair. How many repairs are forever anyway?

That leaking rubber cannot be patched. If the metal grommets are cut off each end, the hose slit and pulled off the metal fitting, you may be lucky and find a length of the correct rubber that can be fixed in place with new grommets at a hydraulic repair shop. Some of the fittings were convoluted at the connection and a pair of hose clamps at each end would keep the connections together.

I was afraid of that.

I’m unfortunately full of questionable ideas and of a math and engineering background, and with all that cheap 134a sitting around who could resist trying?

You’d be surprised at what holds that pressure anyway. Those metal tubes are really thin and easy to bend when they are off. Heck, my road bike tires are inflated up to 120 psi and by the time I get on it on a warm day I’m sure it gets to the 140s.

Just thinking maybe it should be possible. I don’t know.

I’ll think it over and see if I find something that could possibly hold up under that pressure. Otherwise I’ll have to get in touch with a local shop to see if they can replace the rubber section of that hose. It doesn’t seem like it would be possible though.

I haven’t purchased any A/C hose in a couple of years but have done so in the past from various auto parts houses such as AutoZone, NAPA, and so on.
It’s not difficult to make up a hose from scratch and even the various aluminum end fittings and so on can be bought at the parts houses if they’re needed.

Some hoses use crimp fittings which require a special tool. If the car uses something like this you can get a new length of hose and take that along with the existing ends to a diesel repair shop.
Those guys usually have that crimping tool and should not charge you much at all to crimp those ends on.

As to your question about a vacuum, pulling a vacuum will not reveal any problems about the system other than whether there’s a leak or not. It’s just far easier, and cheaper, to lose vacuum than refrigerant while determining if there actually is a leak.

For the hose just go to a junk yard and get one.

If you can remove the complete hose, fittings and all, and take it to a NAPA parts store, most of them can make up a new hose using new fittings or if necessary, the fittings on your old hose…

I don’t believe you will find any R12 for sale in small cans…If you do find some, they will cost more than $20…There is a product called “Freeze 12” on the market which will replace R12…It costs about the same as R134a. Google will find it for you…

@ok4450 @Caddyman Excellent suggestions on the hose, I’ll be checking with NAPA tomorrow.

@oldbodyman unfortunately I have had an exceedingly difficult time finding parts for this car at salvage yards. So much so that I’ve almost considered actively looking for people who have wrecked it or are selling their piles cheap.

The thought of having to just take the risk on something else being wrong is unsettling, but prior to the burst it seemed to be moving the right direction. Once the low side got up to 10 psi I was actually getting some slight cooling at the vent.

As for the R12, I’m not joking on that, it’s around here for some reason and available. I have no idea why, but it’s out there.

Oh, and the Freeze 12 is around as well. I’m actually game for either as I’ve heard either will work just fine in this system, it’s just the R134 that seems to cause troubles.

If you have an air compressor and gauge set you can do the vacuum yourself since there’s no refrigerant to be released.

When you said you had an idea of how to repair the ruptured line the first thing I thought was, oh no I see duct tape coming, sure enough I kept reading and duct tape was involved. I knew it had to be duct tape, because bailing wire wouldn’t work. I don’t know where you are located, but if there are any Pull-A-Part yards around you, you might find a line there. I’m not familiar with BMW’s, but the other end of the line may have a spring lock connector meaning you’d need this to remove the line.

Pull-A-Part usually has a good selection of older cars on their yard that most junk yards would have already crushed, because the demand for parts is so low. The worst thing you have going for you with Pull-A-Part is that the car is a BMW which isn’t as common as a Ford or Chevy. You can find the Pull-A-Part locations and what cars they have in their inventory without even having to go to the yard.

I’d also add a can of compressor oil before recharging with refrigerant.

@FordMan1959 Spot on with the duct tape, though I’ve never used bailing wire for anything, perhaps I should pick some up…

Anyway, I dropped the repair the line idea, after “running the numbers” I determined that I’d rather not risk a repeat failure and that I wasn’t sure any patch I could come up with would hold up to the pressure.

I checked with a few companies regarding fixing or making a custom replacement, but the cost seemed a bit on the high side, so a salvage yard it is. Where I am in Saint Louis pull a part does not have the vehicle I need, however I did discover a yard with a “treasure trove” of 80s 325s and after some research I discovered that the 325 has the same hose, so score there assuming they still have one and it’s in respectable condition. No special connector is used.

As for the vacuum pump, I litteraly laughed out loud when I read that because it’s actually sitting in my car right now. I was supprised one was available so cheaply.

Cayman and others will also likely be happy to hear that with all the deals I’ve found on the various parts to spruce this system back up I’ve also decided to replace the reciever/dryer.

So I should pretty well be set soon, all I need is to talk someone with one of those 30 pound jugs of R12 around here to charge me up a couple pounds after it is prepped and I should be good to go.

You mentioned adding oil, and I guess this is the last item to sort here. I’m aware that these vehicles use mineral oil. I’m also aware that ester mixes fine with any mineral oil left in the system, and it seems to be all I can find. So, should I use ester, or where can I find mineral oil? Certainly I can’t use the stuff in the Walmart Pharmacy, or can I?

That compressor operated vacuum pump will pull a vacuum on the system but it won’t remove moisture from the system. In order to remove moisture from the system the vacuum pump has to pull 1 atmosphere or 29.92" Hg. At this pressure the moisture is converted into gas so it can be removed. And if the moisture isn’t removed from the AC system, the AC doesn’t work very well. And if the AC system uses PAG oil the oil becomes acidic if there’s moisture in the system.


I used one of the compressor vacuum pumps on my '94 Escort just a few weeks ago, the stronger the compressor and pressure of the air the more vacuum it will pull.