fresh air / defrost slider controls

[thehackmechanic]

Ok so having owned this E9 for over 25 years, I still don't completely understand the fresh air / defroster controls and how they interact, or are supposed to interact, or interact by unintended consequence, with the retrofitted but largely stock a/c.

Mine is a CSi so the controls are in German. The middle slider is "unten oben" (down up). I can see it closing and opening the flap at the footwells. The right fresh air slider is "zu luft." I can see it pulling the cable but can't see any flap moving, but it's obviously working.

As per prior post, I've installed a bypass valve on my heater core, but if I flip it to allow heat to the core and open the flaps with the heater slider, unten sends the heat to the footwells and oben sends it to the defrost. In both cases there's a little air coming out the center console. This is all with the car parked, ignition on, fan on high ("lufter"), a/c off. No problem.

I shut off the heat and get the following combinations with the sliders:

oben zu sends air out the defrost
oben luft sends air out the console
unten luft sends air out the console
unten zu sends air out the footwell

Again, all that makes sense from the standpoint of the fresh air (zu luft) slider as being completely independent of the heat.

So here's the question. The a/c retrofit used the rare fragile "intermediate piece" shown as #13 in realoem:

http://www.realoem.com/bmw/showparts.do?model=7031&mospid=47808&btnr=64_0876&hg=64&fg=55

This piece connects the air flow from the evaporator assembly to the air flow from the heater box, and vice versa. This is what enables cold air to come out the center console when the a/c is on (and is missing if you do an aftermarket install).

It seems intuitive that, for maximum cooling, I want the fresh air slider off, as I don't want fresh air; I want it to recirculate. So, off, correct?

Yet, because of the "intermediate piece" connecting the evaportator assembly and the heater box, I seem to be getting some small amount of cold air out the footwells if "unten" (down) is selected, and out the defrost if "oben" (up) is selected. I don't want either of them. I want it ALL to blow IN MY FACE.

Conversely, a big advantage of a/c in modern cars is defrosting the windshield by blowing air conditioned air at it. There doesn't seem to be any setting that maximizes this, yet if I set the slider to unten and literally block the console vents with my hands I can feel the flow to the windshield increase.

Lastly, the blower in the heater box normally switches off when I switch on the a/c blower in the evaporator, but with some creative wiring I can make them independent. Turning the heater blower on while the a/c is on acts like something of a turbocharger, forcing additional air over the evaporator (we all know those a/c squirrel cages are pretty anemic). But unless the "luft" (air) setting is selected, the flap in the console is closed, so I don't get the extra air. But if the air flap is opened, I get outside air, which I don't want.

I have an E9 heater control box around here somewhere I could use to figure it out, but I can't find it.

Anyone with factory a/c have any insight into all this?

--Rob

 

[61porsche]

Heater control

http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/64111140.html#refertoc
Here's the link-

 

[61porsche]

If one were industrious

enough to want to use the heater blower to suppliment recerculation then that someone would devise a way around the heater fan to seal and insulate it. 1/2" neoprene foam cut in a way to tent both sides and the cover.

Similar to that is to stick a thermometer in the heater vent and see if there's air bleed from the top flap next to the heater motor. If the seal across the hood is bad, then engine heat gets in rather than the grilles on top.

I've thought about it until I got the thing to put out 42 degree air. Then you have to move your knee to keep from freezing.

The other thing is air infiltration. A car moving at speed can evacuate cabin air just like in your house. Things like the shifter foam block, the door panel plugs for the window motors, a door seal can effect the inside temps. So I went through and methodically closed things up so to speak.( Yes, even the parcel tray speakers.)

 

[vraned]

Rob,
The output of the ac unit feeds directly to the center console vent. The "rare" ac duct has an openinig between the fresh air flap (4) and the center console vents. That is the only connection betwwen heater box and ac unit. Cold (ac) air from floor or defroster vents (depending on the position of 3) means that the fresh air vent (4) is not closed. This could be as simple as a cable adjustment, but could also indicate deteriorated packing on the (4) flap. This material was effectively gone in my heater box. (heater box section on vranedom.com)

Since you have installed a heater core valve,turbocharging the ac with the main fan could be accomplished by feeding the floor vent output into the squirrel cage inlets. Anything coming from the fresh air side (4) would dilute the cold air, and might even present enough pressure in the fresh air duct to defeat the weaker ac fan.

 

[61porsche]

Infiltration

Here's a timely link from te 02 guys-

http://www.bmw2002faq.com/component/option,com_forum/Itemid,0/page,viewtopic/t,373116/

 

[thehackmechanic]

Thanks guys, that clears up a lot. Will check the cable adjustment on the fresh air vent; anything else will have to wait 'till after The Vintage.

 

[thehackmechanic]

Are the Following Statements Correct?

I want to resurrect this thread and the idea of using the heater box fan to turbocharge the a/c evaporator squirrel cage fan, but first I need to fully understand how the heater box works. I'm a left-brained guy who finds it hard to visualize things unless they're sitting right in front of me, and I don't have the heater box out of the car. I've looked at the illustrations that 61Porsche posted, and at Vraned's site with the opened-up heater box, but I want to make sure I have this right.

Are the following statements correct?

HAVING NOTHING TO DO WITH AIR CONDITIONING...

--The flow of fresh air comes into the car through the fan at the top of the heater box.

--The left-most slider (#2) both opens the top flap that allows the flow of air into the heater box, AND ALSO turns on the fan.

--The fan is on the outside, the top flap is on the inside. Air must pass through the fan -- whether or not the fan is running -- and THEN is allowed into the heater box via the top flap.

--If the top flap is not open, no air (other than what bleeds past the flap) enters the heater box, so even if I jury-rigged the fan to turn it on without opening the flap, it wouldn't work -- it wouldn't be pushing extra air into the box; any air would be stopped by the closed flap.

--Slider #4 (fresh air flap) allows fresh air into the passenger comparment through the center vent.

--If slider #4 (fresh air flap) is open but #2 (top flap) is closed, in theory, no fresh air enters the car, but in practice some may due to degradation of the foam seals on the flaps.

--Heated air NEVER comes out through the center vent -- only through the defroster and footwell vents, in proportion dictated by slider #3.

--But the fan, when on, pushes all air equally -- fresh air out the center, and heated air out the footwells and defrost.

--Due to the Byzantine nature of these controls (my 911 was similar), if one wants to defrost the windshield but not have cold fresh air, one must:
--Slide #1 to the right to open up the heater flap
--Slide #2 to the right to turn on the fan (which also opens up the top flap but it doesn't matter)
--Slide #3 to the right to point the hot air up
--Slide #4 to the left to turn the fresh air off


AIR CONDITIONING

--Slider #2 (the top flap) should be closed, as you probably don't want fresh air coming in; you probably want it on the equivalent of "recirculate," even though there's no such setting.

--As Vraned says, slider #4 (fresh air flap) should be closed to prevent air conditioned air from blowing back into the heater box and escaping through the footwell and defroster vents.

--If there IS cold air escaping through the footwell and defroster vents, it means that the cable is out of adjustment and/or the foam on the fresh air flap is degraded.

Do I have all that right?

If so, extra-credit questions regarding "turbocharging the evaporator squirrel cage fan." Are the following assumptions correct?

--61Porsche recommends that I block off the fresh air that would normally flow through the fan by making a "tent" under the hood around the fan.
--This would make it so I can use the #2 slider to open the top flap and turn on the fan, but to push air through the box without allowing new fresh air in. (I would need to modify the wiring to allow the heater box fan to be on at the same time as the evaporator fan; right now, turning on the evaporator fan switches off the heater box fan.)
--There is some question as to how much air it can push without having new air coming in behind it (kind of like having a box fan in a closed window).
--If I do this, the #4 fresh air slider must be open to allow this extra air to come in from the heater box and for some of it to presumably wash over the evaporator.

--Vraned offers a different solution -- to direct the air being output from the footwells into the sides of the squirrel cages.
--The intent of this is to get air DIRECTLY into the evaporator (as opposed to the "tent" solution, which gets air into the evaporator indirectly).
--If I were to do this, the #4 fresh air slider should be closed.
--I doubt this would be worthwhile, as the amount of air coming out the footwells does not constitute a torrent.

--The more direct but aesthetically inelegant solution would be to bolt a high-output computer pancake fan right onto the side or sides of the evaporator assembly. If you're going to turbocharge the squirrel cages, turbocharge them directly; don't screw around, right?

Comments??

--Rob

 

[HB Chris]

All of your assumptions are correct about the levers. However:

When the AC is turned on it opens the relay for the heater fan making it inoperable. This relay is always on, opposite of what most relays do. I can't see where using that fan would turbocharge anything and if it did I wouldn't cover it. If you have good hood seals it is bringing in fresh ambient outside air, not hot engine air.

 

[Tundra]

I can see it pulling the cable but can't see any flap moving, but it's obviously working.

As you know I recently had the 'enjoyment' of having to pull out the evaporator.
I've learned a few things during this process one of which is new curse words.

Kidding aside, just because you see the cables pulling does not mean its working.

There are 4 cables, Bowden cables (?) similar to the hood cables. Each flap cables have the inside wire secured to the flap lever via a bolt. The entire cable is then secured by a clamp to the flap lever slightly above this bolt. If this clamp is broken or loose, then when you move the lever you will see the cable move but the wire inside, which pulls the lever, will not and so the flap will not open and close.

This link from an excellent post from Bwana clearly shows how the cables are attached, bottom 3 pictures, and the clamp I'm referring to.
http://www.e9coupe.com/forum/showthread.php?t=7739&page=2

Not sure if this is your problem but I would check to make sure these clamps are secure. There are four of them.