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Budget AC Repair FAQ

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Courtesy of Mike Wassall (Mike W.)

Air conditioning didn’t seem to have the highest priority for the fine German engineers, most likely due to their mild climate, but it actually worked pretty well by the later years of the E12 series.  Read on and find out how to resurrect your A/C for a minimal sum of money.  The A/C in my 528i was fixed with 2 hose repairs and a full charge of R12 (when it was available) and with a slight top off, (and I mean slight) has lasted 165k.  And it blows cold air, and has probably lasted longer than the original did.  Last major trip I made in it, it was blowing 42F air with the compressor cycling on and off and temp set about mid point for A/C.  That was the desert sun between Laughlin and Las Vegas in August with a temp of about 108F.  Not bad for a 20 year old car.

It only blows hot air, how come?  As you had probably guessed it is likely out of freon, or R12 or whatever you want to call it.  The most common problem is the hoses seem to become porous with age, the freon just leaks right through them.  The heavy duty, very stiff, usually red colored hoses seem to be the worst, they are steel reinforced and will probably withstand who knows how much pressure before they burst, but they do leak as they age, and not just at the fittings as often happens with many systems.     I think replacement hoses are still available, there is a much cheaper solution.  My local NAPA auto parts store carries bulk A/C hose, I think it is around $4 a foot these days, a steal compared to the new dealer price for a hose and it is the barrier hose that can be used with 134a.  It isn’t even all the hoses that leak, the one from the compressor to the condenser is the worst, followed by the one from the condenser to the drier.  Those two have to deal with the highest heat and the most pressure so it does make sense that they would be the shortest lived.  Again, they become porous, they don’t have a hole blown in them so don’t be surprised by the lack of it.  And if you are going to charge it with 134a, be sure to replace the suspect hoses, it is a smaller molecule and is more prone to leaks and the new hose is a “Barrier“ hose, meaning it has a plastic like liner to prevent leakage.  It can also spring a leak from many other places in the system, so check out hoses and fittings especially.  The real telltale is oil.  Refrigerant contains oil in suspension, so if it leaks refrigerant, it will also leak oil.  Check everywhere, snug down all accessible fittings, not super tight, don’t strip things, but tight.  Check the condenser, right out in front it is most at risk for damage of the non-hose components.

Hose repair:  This is the single most important thing here, and the most likely cause of your  A/C failure.  The original fittings come right apart, I don’t know just how much force it took to screw them together originally but it was a whole lot, you aren’t going to put it together quite the same way.  Unscrew the fitting out of the hose, yes it just screws right out.  The collar unscrews also, but you don’t need to bother, you don’t reuse it.  Measure the inside diameter of the hose, but not where the fitting screwed in, somewhere in the middle, and measure the hose length and get a new piece the same length.  You may need the right size, or maybe the larger size, particularly on the 13/32 size, I have always been able to get them in, but sometimes with more work than should be necessary, including reaming and lubing up the hose.  And you want to get it all the way in, up to the shoulder.  You may have to lube it up a little, but keep it clean, you don’t want to plug up the expansion valve.  Use a hose clamp, I use two since there is room and we are talking high pressure here, maybe up to 300 PSI on a hot day.  Now if you have or want to put on something special like a cold air intake or the like, now is the time, things are apart and you can custom size and fit your hoses right where you want them.  With a flaring tool, you can even run new copper line where you want, it is easy.  The hose sizes are kind of funny, I think it goes 1/4, 5/16, 13/32, 1/2 and 5/8”.  It also goes by refrigeration numbers which I think are 6, 8, 10, and 12, but I always just give them the fractional size, they complain a little, but always get the right stuff, it is marked on the hose itself.  Remember it has to hold a lot of pressure, so get it in there good and solid and use new good quality hose clamps and get them good and tight but don’t strip them.  When you bolt up the hoses to the fittings on the compressor or the like, be sure to use new copper seals, you may have to go to the dealer, and yes they are overpriced, but it is cheaper than a leak because you tried to save 5 or 10 bucks.  Different BMW’s and other cars used different fittings, some of them reusable some not. You need some type of a barb or lip on there so the hose doesn’t blow off.  On the smooth, non-reusable type, I have reused them by silver soldering a steel ring on there.  But you need to braze or silver solder it, regular solder is too soft for the pressures and temperatures of an A/C system.

 

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Charging:  There is already a good FAQ on charging so I won’t really go too much into that, but I will on refrigerants.   Remember I said, repair on a budget, and unless you have a stash of R12, which is currently going for $50 to $75 a pound you could go through a couple or three hundred just having it charged with R12.  But there are alternatives, the most common and accepted is R134a, which works with very similar pressures, but many have complained it’s performance is only so so.  R134a is cheap and environmental friendly, so if you change your mind about things it isn’t a killer financially.  For peak performance you need a larger condenser with 134a, the bigger the better as long as it fits and you can connect hoses to it and mount the aux fan properly, and if you are going that route, I would also recommend going to an aluminum condenser, it really does conduct heat better.  I’m not sure if it is aluminum or not, but I think the condenser off a E23 seven series can be shoehorned in there, and it is much bigger and provided respectable performance on the larger cabined sevens.  I know you think yours looks like it is aluminum, but it just has aluminum fins and copper tubes if it is stock.  And don’t forget about the auxiliary fan, it is essential for even fair A/C performance.  Test it, like I said, it has to work for the system to work right, a common problem is a bad resistor that is mounted on the front of the fan assembly, they can break and fail or just fail without any visibly signs.  It may even be necessary to take the motor apart and grease the bearings, I have had to do that when it had too much turning resistance, and that was the only problem.  But if you go to 134a you need to change the drier and add compatible oil.  Not should, like you should whenever you have the system open, but you need to or else you will smoke the compressor.  But there are other alternatives, Freeze 12 which seems to be mostly 134a reportedly gives better performance, it is a blend with some other stuff in it, but you may need a license to buy it.  And then there is Enviro-Safe, which describes itself as a hydrocarbon refrigerant, a blend of two or three different relatives of propane and butane, but perhaps less flammable.   I have heard good reports on that product, but not used it myself.  I don’t think you need a license to buy it either, and while it is supposedly best when undercharged slightly, they say you don’t need to do a drier replacement or oil change, except for legal purposes.  And of course the internet is a good place to find it.  Another alternative is propane.  Yes, that same stuff as in a propane torch, you can charge your system for the cost of a $3 bottle.  And I have heard some say the HC (hydrocarbon) refrigerants are better than R134a.  Yes, it is flammable, but propane does have a high flash point, if you have ever used a propane torch, you know you can’t relight it from a red hot piece of metal, so unless you have something over 1000F in the location where you spring a leak, it isn’t really much of a danger, but do be aware there is some.  One would use about a pound of HC refrigerant, which by means of comparison is less than a quart of gasoline.  On the other hand, a propane torch will burn for a long time, so use your judgment.  And apparently you do not have to change the drier with this either.  I first heard of it being used in automotive applications since the early 90’s apparently with good success, and it is also used occasionally in commercial refrigeration applications.  If you are using a flammable refrigerant, don’t overcharge, there isn’t a high side cutout switch on E12’s and you don’t want to over pressurize a flammable gas.  I don’t think propane or enviro safe are actually legal, so I don’t recommend them because of that, but do as you think appropriate.  Do, however make sure you add a little oil, whenever there is a leak you loose oil and you don’t want to go to all the trouble of fixing things just to run it out of oil, and do use the right kind, R12 and 134a use different and non compatible oils.  Disclaimer: If you are reading this, you can access much information, some of it contradictory, about the legality of alternative refrigerants, I’m not telling you what to do, or what is legal, just what you can do based on a combination of what I have heard, read and done.

 Compressors:  The big long cylindrical Bosch swashplate compressor is very dependable and long lived, I think the original is still in my old 528i with over 370k on it.  Admittedly it has only vacationed in Las Vegas, not lived in the desert, but that is still a very long life.  And as a point of interest, the clutch can be changed in place without discharging the system.  If you have a York compressor, they are the square one, and I think a few early E12’s came with them, they work, but are noisy and rough, and have rubber mounts that like to fail.  I don’t recommend them.  If your compressor is toast, look for a new used one in the junkyards.  I would look for one off an E12, as it will have the right fittings on it and doesn’t run all the time like many of the E23’s.  Low mileage though always better is not essential, but check it to make sure it turns over smooth, both the clutch bearing and the compressor itself, which should have some resistance, but it should be compression, not friction. If you do or have done a 3.3 or 3.5 conversion you will need a different compressor bracket as the larger harmonic balancer will interfere with the stock A/C bracket.  These are most easily found on early E23’s.  If you have done a 3.5 conversion you may have a wing cell compressor on your car, it is short and round.  It works well, but isn’t as smooth as the swashplate compressor, and there are several different variations that take different mounting brackets.  Also, most or all of them have a different type of hose connection called tube O, as opposed to the flare type that originally came on E12’s.  Not that big a deal, but a slight complication.


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Miscellaneous:In no particular order here are some things that you need to either have it work or work well.  The auxiliary fan in front of the condenser must be working for the A/C to work well and even if it is, it won’t work quite as well in stop and go traffic as when you are moving. That fan should always come on with the A/C compressor, but low speed is very quiet, so look and make sure.  They do like to blow fuses and melt the fuseholder, (another FAQ) and the low speed resistor (mounted on the front of the aux fan) can go out also.  And of course, the motor or the bearings can go, or may simply have to be regreased as I have done in the past.  If the interior blower doesn’t work, it could be several things, the motor itself, which is unlikely but possible, or the resistor pack if it runs on high only, or the microswitch which is operated by the temp control knob and is on the back of the heater controls.  It can either be physically broken or have burned contacts inside that you can’t see.  That microswitch can cause intermittent failure of the blower also.  It in turn operates a relay that could be a problem also, but not likely.  And if the compressor won’t turn on, or is either always on or always off, it points towards the thermostat, which could have a kinked or broken sensor or just have failed mechanically.  And a little shot of oil doesn’t hurt it either, it will make operation much smoother and easier.  It too is located off the back of the temp control knob, a silver box about 1 1/4” square with a lever on it.

(Peter's note: also check heater control repair information here.

 Armed with the above information you stand a very good chance of restoring effective air conditioning to your E12.Now I don’t claim to know it all, but I will answer what questions I can if you e-mail me at mgwwassall@cs.com

 

Mike Wassall

 


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