Date: Wed, 13 Dec 1995 10:34:48 -0600 (CST)
Subject: Re: E28 heat/AC
> Whatcha' got is BMW's idea on how to improve AC performance after
> complaints that the E28 AC system wasn't up to US weather. The
> entire AC system is seperate from the heat system on the car,
> complete with it's own blower (right behind the grills under
> your radio in the console).
> The basic functionality of the AC system is below that of
> the old add-on systems they used to hang under the dash as
> aftermarket AC on Euro cars in the 1970's.. only real
> improvement is you don't hit your knees on it.
Actually, I don't think BMW did it this way to "improve" A/C performance.
They just did it because of the lineage of the car. If you take the
interior apart, the HVAC system is very similar to the system in the
E12 cars. This makes sense, as the E28 had a lot of carryover parts
and designs from the E12. (the doors are the same, just with slightly
different skins; I think the roof panel is the same too.)
The E12, being originally introduced in 1972, did not have anything
resembling combined heat/AC. BMW probably didn't have any idea
what that was back then...... But when A/C was added to the earlier cars
(2002/Bavaria/CS/E12), they did so using a completely added on system.
The infamous 530i A/C problem stems from this -- all of the pre-'78
cars use the same sized evaporator/blower assembly. Adequate in a
2002, but forget trying to keep a larger car cool when it's really
hot out. The evap/blower assembly was enlarged on '78-up E12/E24
cars, and these units are basically the same as the ones that went
into the E28 cars (there were some minor changes, like electrically
controlled flaps and such that were added along the way).
For some reason or other, probably due to space limitations and cost
of redesign, the E12 HVAC system was more or less transferred to
the E28. This is also why the face vents don't blow warm air -- the
face vents on the older cars were designed just as ventilation outlets,
not heat outlets. So if the system seems as functional as an old add-on
system, that's probably because that's what it is....
> I also find some other unique features of the heat/AC
> system to be quaint - the marginal operation of the
> defroster - really it's only good as a defogger - and
> not a very good one at that (better than Jag's used to
> have - but not a lot). The fact that the sensor for
> the temperature is located (wait for this!) right
> over the drivers left toe. So you can be sure - absolutely
> SURE that this toe is comfortable!
Again, just think about it as adapted carryover stuff from a 10
year old design, and it begins to make more sense. The defroster
doesn't seem too bad to me -- but I'm used to 2002s, where the
defroster is lucky to clear the lower 1/4 of the windshield on a
really cold day.... :)
> Try as I do - it's part of the charm of the car.. so expensive
> and such a sucky heat/AC system! And - count yourself lucky..
> you don't have an older 7 series where the controls tend to
> freak out and are SUPER-DUPER expensive to fix or replace!
Well, at least the E23s had a newer design system. Temp sensor mounted
high up, defroster that runs the A/C and works with a push of the
button, low temp cutout, warm face vent air (I think), etc....
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