E28 Evaporator core vs. E12

[0257]

Thanks, will try my hand at it. Meantime, using spares I have gathered I have tentatively determined that en e28 blower motor and cages will fit in my e12 evap box. The e28s were the first really successful BMW sedans in the US, and it’s said that improved a/c was a big part of their success. The fan has nominally the same dimensions as my e12 fan,but with plastic cages (instead of metal) that have no compartmenting divider, much skinner edge surfaces and fatter, more aggressively angled (that is to say, straighter) blades. When I connect the e12 fan to 12v I get a buttery smooth spin-up and decent air. When I connect the e28 fan, I get a less refined but definitely stronger airflow. So I think I’m going to buy a new e28 blower motor from BMW ($410) and install it. Expensive, yes, but you have to ask yourself how many times you want to remove the center console….

Next, experimenting with evaporators. The e12 evap stands about 7.75” tall, is 10” long and 3 3/8” fat (with another 1.5” of pipes along the back). The evap box cavity measures almost identically, with a few quirks. Might be able to squeeze out another 1/8-1/4” rearward (toward the blower box) with judicial shaving of ABS. So, it would be great to find an evaporator with greater efficiency that fits in that space with a modern expansion valve…. Between stronger fan, better condensor and more efficient evaporator we’d be approaching “modernity”. If anyone knows about such matters I am ready to take this to the next step and now need to get oriented to how to find the right candidate evaporator.

K

[Mike W.]

You might be onto something with the blower, but it might be in the ducting too, I believe Es 12 and 28 use the same heater blower but E28s put out more fresh air. At worst I don't see it hurting as long as it fits. And the way E12s use one air output for 2 different sources is not a good design, again, E28s did that much better.

Now I'm no refrigeration engineer, but it's my understanding that the condenser is the limiting factor, not the evaporator. All the successful R134a conversions seem to use a larger, more efficient condenser leaving the stock evaporator in place. Typically a parallel flow condenser. But perhaps contradicting myself, on my long ago Bavaria I upgraded the compressor to an E12 one from the stock vibration master York, replumbed everything with new lines and hoses and put in an E21 aux fan in place of the tiny little stock which I think was just a 3 blade, maybe 5, with no shroud. But while it was smoother, quieter and leak free, it didn't really cool any better, and believe me, that E21 fan moved a whole lot more air than the original one. Smallish blades, but a shroud, 11 blades and larger diameter. But this was long before I had internet access and I left the stock condenser in place, which again seems to be the limiting factor.

On the third hand, I blew the fuse on the fan on my E12 528i one time and it hardly did any cooling until I replaced it. And that car would blow 42F air in 100+ temps in the desert on the highway with the compressor cycling.

[Robert Bondi]

Yeah, agree with Mike and definitely think the duct work is lacking on the E12 even without a comparison for reference. I'm just not seeing much in the way of dedicated ventilation passages on the restoration car in the center console region. My new fan blower (e28?) does seem the same as the E12, just some differences on the squirrel cages. I have a couple pictures to add to the discussion. For the sake of our purposes, I'm assuming 79 E24 is the same as E12 which is my general understanding.

Note the two extras rows (or maybe 2x1/2 rows of tubing on the E28 evaporator). My reasoning for going E28 is different.....I'm starting from nothing on a non-AC car so E28 parts are just a bit easier to find and I like some of the design aspects on the E28 parts.....all aluminum, o-ring seals, etc....




Some extra views of the same in this gallery:
https://www.flickr.com/photos/robertbon ... 297675328/


Robert

[0257]

Bob, great post. I was right behind you finding that 4Seasons evaporator coil. One question: do the pipes on that evap coil exit at a higher level than on the other coil? Because the resistor is mounted internally in my box, just north of the pipes, if the exit point of the 4Seasons is higher it could be a problem. Suppose I might be able to bend them downward if necessary….. Ken

[Robert Bondi]

No, the 4seasons evap core is also overall notably a little shorter in height. My gallery link has better direct side shots if I understand your question correctly. Here are two more specifics photos in that gallery:




Hope that helps...

Bob, great post. I was right behind you finding that 4Seasons evaporator coil. One question: do the pipes on that evap coil exit at a higher level than on the other coil? Because the resistor is mounted internally in my box, just north of the pipes, if the exit point of the 4Seasons is higher it could be a problem. Suppose I might be able to bend them downward if necessary….. Ken

[0257]

Mike W and Bob: I think it’s finally sinking in — there are NO ducts on the path to the side a/c outlets! At all! If my eyes are seeing correctly, there’s just the space between the dash cap and the metal dash support tray, which more or less forms a conduit. Kind of an incidental conduit. And I note that there are lots of little voids and holes along the path. Sigh. So UNdeutsch ist das.

Now, all that being the case, it makes me wonder if a mini-fan in the duct itself, wired into the a/c, might not be an answer. Might pull more air through the turbulence and deliver it out the sides. Call me extreme, but extremism in the pursuit of cold a/c is no vice!

[0257]

Serious question: has anyone ever measured airflow in cfm at the outside vents?

[tlake]

I don't have a cfm reading, but Road Test magazine measured the air out of the 1975 530i's vents as approx 40F. The stock system will make cold air on R12, if you have no leaks and everything is as it should be. The e12's problem was more air distribution, and as mentioned above by Robert Bondi, the related issue of a lack of ducting.

Cover the dash with material and get a quality window tint, that helps.

[Mike W.]

Serious question: has anyone ever measured airflow in cfm at the outside vents?

Less than a heavy breather.

I don't have a cfm reading, but Road Test magazine measured the air out of the 1975 530i's vents as approx 40F. The stock system will make cold air on R12, if you have no leaks and everything is as it should be. The e12's problem was more air distribution, and as mentioned above by Robert Bondi, the related issue of a lack of ducting.

Cover the dash with material and get a quality window tint, that helps.

I wonder what blower setting they were using? Output temp is related to airflow. Plus looking at Realoem I see E12s up to 2-77 used one blower and evaporator, and that blower was the same one as on E3's. I had one of them and it was a fraction of what my 528i E12 put out air wise. And they continued to make improvements, after 2/77 they got a different blower and evaporator, in '79 they got a different condenser and aux fan. I used to see 42F temps on the highway with the temp about midway, the compressor cycling blower speed the one below max. It could have gotten colder, that was as cold as I wanted it though.

[tlake]

Serious question: has anyone ever measured airflow in cfm at the outside vents?

Less than a heavy breather.

I don't have a cfm reading, but Road Test magazine measured the air out of the 1975 530i's vents as approx 40F. The stock system will make cold air on R12, if you have no leaks and everything is as it should be. The e12's problem was more air distribution, and as mentioned above by Robert Bondi, the related issue of a lack of ducting.

Cover the dash with material and get a quality window tint, that helps.

I wonder what blower setting they were using? Output temp is related to airflow. Plus looking at Realoem I see E12s up to 2-77 used one blower and evaporator, and that blower was the same one as on E3's. I had one of them and it was a fraction of what my 528i E12 put out air wise. And they continued to make improvements, after 2/77 they got a different blower and evaporator, in '79 they got a different condenser and aux fan. I used to see 42F temps on the highway with the temp about midway, the compressor cycling blower speed the one below max. It could have gotten colder, that was as cold as I wanted it though.

Hard to say, the e12 had the e3/e9 variable speed resistor type in those days. Realoem isn't always consistent, I have seen their listing say the e3/e9 and e21 had the same evap core and blower, at the same time they also said the early e12 and e24 630CSi shared a/c parts. From what I can see the e12 and e24 evap core / blower parts looked very similar.

BMW's figures were the e9 coupe had a 4,500 kilocalorie Behr a/c system, and the e24 630CSi had a 6,200 kilocalorie per hour system, and the latter system was partly developed in Texas and Arizona, that's what R&T's Ron Wakefield relayed anyway. I would say for any given time the 5 and 6 series would have shared parts. BTW a slower fan speed produces colder air, since the air passes over the cold evap coil slower. Of course you don't want it getting much colder, otherwise the evap core can freeze up and block airflow.

[Mike W.]

Yes, that was my point, the more airflow the higher the temp will be. The expansion valve "should" keep it from freezing up but I had my first E12 freeze up one time when it was just a tiny bit low on charge. Noticed the lack of airflow and when I stopped to get gas a huge puddle formed under the car as apparently it was just barely frozen. Worked fine the rest of the vacation.

I recall a figure of 17,000 BTU for I think it was an E12 from long ago but that corresponds with your 4500 KC number for a Bavaria. Maybe I was thinking Bav? But both number may be theoretical, I mean 17K BTU is a big window A/C unit and as hostile an enviornment as a car is, it's a small space to condition let alone if it's the higher 24K number. The latter would be a HD 240V window unit at home.

Since you mentioned the variable speed blower, which on maximum should be full battery voltage, not going thru the transistor, it might be worth investigating to see if the blower is in fact getting full voltage, over the years resistance forms at every connection. On that subject back in the 90's I had an E24, an '80, that had huge resistance somewhere. Probably ground but I didn't look too hard. But everything electrical was low, lights were dim, wipers were slow, A/C blower wasn't much, although 10X better after I kludged an E12 air hood on top of the dash. But after 45 years now on E12s a cleanup or even dedicated new circuit for the blower might be in order.

[tlake]

Yes, that was my point, the more airflow the higher the temp will be. The expansion valve "should" keep it from freezing up but I had my first E12 freeze up one time when it was just a tiny bit low on charge. Noticed the lack of airflow and when I stopped to get gas a huge puddle formed under the car as apparently it was just barely frozen. Worked fine the rest of the vacation.

I recall a figure of 17,000 BTU for I think it was an E12 from long ago but that corresponds with your 4500 KC number for a Bavaria. Maybe I was thinking Bav? But both number may be theoretical, I mean 17K BTU is a big window A/C unit and as hostile an enviornment as a car is, it's a small space to condition let alone if it's the higher 24K number. The latter would be a HD 240V window unit at home.

Since you mentioned the variable speed blower, which on maximum should be full battery voltage, not going thru the transistor, it might be worth investigating to see if the blower is in fact getting full voltage, over the years resistance forms at every connection. On that subject back in the 90's I had an E24, an '80, that had huge resistance somewhere. Probably ground but I didn't look too hard. But everything electrical was low, lights were dim, wipers were slow, A/C blower wasn't much, although 10X better after I kludged an E12 air hood on top of the dash. But after 45 years now on E12s a cleanup or even dedicated new circuit for the blower might be in order.

Same here, years ago when the temp control wasn't working and the compressor ran all the time it froze up after around 45 mins, and you could tell with the reduced airflow. I managed to get a brand new temp control dial switch from BMW, still available and made in Italy, for the early e12s and it's working well. However, the blower switch has been unavailable for years. Mine has a dead zone between 67% and 99%, but I just turn it just before that, and can still use 100% when I want. I dare not take it apart because it's on the unobtanium list

The South African reports on the 528 in 1975 and 1976 said the factory a/c was effective. In the mid '90s I sat in a e3 3.0L long wheel base and the a/c was good on a warm day. Maybe they made small improvements in late e3s? BMW like others makes small changes from time to time, which can be a problem because you get a surprise when things don't work or fit.

I was reading on the 1967 Mercury Cougar only 2 in 10 cars had a/c. However, in Road & Track's e3/e9 survey 79% of the cars had a/c, and their e12 530i survey mentioned 65% had a/c. So a/c's popularity quickly rose through the '70s. It used to be a rarity on Corvettes, but became standard in 1980, and I think the 528i also had it standard. Most people wanted it by then. Such a shame they keep changing the gas, life would be easier if we stuck with R12.