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Project planning: Heater blower upgrade light version
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Wed Oct 06, 2021 2:30 pm    Post subject: Project planning: Heater blower upgrade light version Reply with quote

Good morning all!

Last friday I drove through pouring rain for hours in my MY 1981 931 ( early heater ) for the first time. That heater really IS pathetic. I cleaned all contacts when I got the car, changed the brushes on the blower motor, refurbed the heater controls... and still, as opposed to the later-style heater in my n/a, this early heater is unacceptable. I won't have that.

I'd have loved to implement the later-style heater in that car, but reading up on what that entails, I don't think I want to go down that road.

So... I came up with an idea. After speaking to an HVAC technician about the effectivity of axial as opposed to radial blower motors under the given circumstances of the heater matrix we're dealing with, I thought maybe if I manage to McGyver the later blower motor into the early matrix and ditch the flap under the cover, the air flow might improve just enough to make defogging acceptable.

Also, being able to pull the blower motor from under the hood instead of having to take the dash out and pull the whole matrix sounds GOOD.

I wonder, am I the first to have this idea, or has any of you done some investigating down this road? What are your ideas? Feasible? Any pointers anyone?

Fortunately, my workshop has both heater boxes as spares, so I hope to compare them and take measurements soon. Maybe it's possible to cut off the "funnel"-shaped bit where the later blower motor sits and fit it into the spot where on the early matrix, the six strips holding the early blower motor are attached. I have learned ABS welding...

Let me know what you think!

Eliza
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Wed Oct 06, 2021 4:41 pm    Post subject: Reply with quote

You need different wiring and controls for the later heater, its a big change to the car, it really is. Perhaps a modern fan would do a lot better...perhaps it would spin faster at the same voltage and perhaps the fan blades would be more efficient at moving air?

So to upgrade the old style system i would look into a modern fan instead of changing from early style to later style.
The later style is enough in all conditions, but like i said...its a lot of changes to the car.
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924RACR  



Joined: 29 Jul 2001
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Location: Royal Oak, MI, USA

PostPosted: Wed Oct 06, 2021 8:53 pm    Post subject: Reply with quote

I have contemplated it (with a much later donor), the biggest complexity in my mind will be managing a completely different flow direction, hadn't yet wrapped my mind around how best to achieve that, particularly while retaining the ability to get at the motor from the underhood side...
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Vaughan Scott
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Wed Oct 06, 2021 9:17 pm    Post subject: Reply with quote

Morghen, I like your thinking. Very much indeed .

Vaughan, your input is much appreciated - especially with HVAC applications, I tend to underestimate complexity. So thanks for a timely reminder, before I go hacking away and find out days later that my heater blower s***s even more than it does now ( should probably be, s***s less? Oh, whatever ) .

I just re-read a few older topics and may have found a fan that'll do the trick, PLUS it will be mounted from under the hood. Just a little request :

Anybody have a chance to take a measurement of the inside diameter of the heater matrix, where the blower motor fan blades sit? I'd hate to buy too large a fan...

Ooh this is exciting! Imagine it works and I'll have AIRFLOW.. and DEMISTING.. and all that!

Thanks in advance!

Eliza
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Wed Oct 06, 2021 11:17 pm    Post subject: Reply with quote

Be sure to report your result as a buddy has an early 924 and he is suffering as you are.
As a matter of fact i have to go have a look at his car today as he has my supercharger kit installed and i need to check and adjust the fuel mixture on his car...so i could try to measure the fan diameter.
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Wed Oct 06, 2021 11:43 pm    Post subject: Reply with quote

Morghen, that would be awesome!

I'd rather know the inside diameter of the box than the outside diameter of the fan itself, because the fan I found has a plastic round cage frame that needs to fit into the hole going down towards the heater core.

Once I have the new fan installed and tested I'll let you know a) how it went and b) what the effect is

Eliza
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Eliza  



Joined: 17 Aug 2015
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Location: Prov. Utrecht, The Netherlands

PostPosted: Fri Oct 08, 2021 3:37 pm    Post subject: Upgrade v2 Reply with quote

Hi Morghen,

did you have a chance at all to measure the heater box on your friend's car?

Anyways, I decided if I do dive into the heating system of my car, I might just as well change something else that´s bothering me. I want hot air out of the center and side vents. Very do-able, apparently.

Instead of connecting the under-dash ducts to the large outlets on the heater matrix, the later heater box has these large outlets plugged and the cabin-facing underside of the box open, like in the photo below.

.

The old heater matrix is shaped essentially the same, but has that opening covered in plastic, just about visible here:



I am now sourcing three additional parts off of a later car, ref. no.s 1, 2, and 10 in PET:



Once the opening in pic.2 is cut free ( I´ll use a soldering iron to do that in the car ), in goes adapter no. 10, into that goes mixing chamber no. 2 and the the later style vents no. 1 from the dash front. I´ll then plug the round cold-air outlets and that should give me heat from the dash vents


Can´t wait for the parts so I can get started!

Eliza
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morghen  



Joined: 21 Jan 2005
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PostPosted: Fri Oct 08, 2021 4:07 pm    Post subject: Reply with quote

Didnt manage to visit my buddy but he’ll visit me in 1h and then i’ll try to measure the diameter of the opening.
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Eliza  



Joined: 17 Aug 2015
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Location: Prov. Utrecht, The Netherlands

PostPosted: Fri Oct 08, 2021 10:09 pm    Post subject: Reply with quote

Nooooo worries!

Eliza
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morghen  



Joined: 21 Jan 2005
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PostPosted: Fri Oct 08, 2021 10:47 pm    Post subject: Reply with quote

So, the metal opening is approx 210mm across.

There is some plastic housing for the original motor that would need to be cut if a complete new motor would be used.
Meaning the housing has some beams across the 210mm opening and the motor is suspended on those.
The oem motor is actually suspended in the middle, inside a 60mm diameter rib/reinforcement.
So either find a motor that has the body 60mm and place it inside the original housing somehow...or just remove the support for the original motor and use an aftermarket one.

A quick search on my local aftermarket parts website finds this stuff...i would like to try this on my buddy's car.
https://race-shop.ro/ventilatoare-12v/53869-ventilator-electric-universal-spal-190mm-aspirare-12v.html


Also, check your PM inbox.
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Fri Oct 08, 2021 11:02 pm    Post subject: Reply with quote

Hmmm, that's a very interesting idea for a simple replacement, easier to implement than a radial (squirrel cage) fan since it's still axial, but definitely flows a lot more air. Not sure of the price conversion, though - seems quite expensive?

For comparison, here we have an 8" racing fan (about 203mm, would need to check overall outer dimensions) for about $20USD:
https://www.summitracing.com/parts/sdm-pce185-1018

I could definitely be tempted to hack that in... OK I see indeed overall size is shown as bigger, up to 8.875" (225mm), but with some judicious trimming maybe that'd be easy to correct...

Could stand to do this to the racecar too; racecars need defrost/demisting too!!!
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morghen  



Joined: 21 Jan 2005
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Location: Romania

PostPosted: Fri Oct 08, 2021 11:16 pm    Post subject: Reply with quote

Everything is more expensive in Europe, dont you know?
Translate that to USD and it would be about 85USD.
Obviously thats just for reference and as an example....i'm sure better fitting and better suited fans exist out there and definitely cheaper ones exist out there.
The one i linked is a radiator fan...so maybe blowing quite a bit of air...maybe too much? i'll try to connect one to the wires of the heater motor to see how fast it spins and how much air it pushes...my concern is that even at lowest speed it will still be too much...but needs to be checked and tested.

I probably wont have too much time to work on my friend's car any time soon as i'm busy with my supercharger kit production but if you guys give it a try, dont forget to post here.
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MikeJinCO  



Joined: 08 Jun 2010
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Location: Maysville, Colorado

PostPosted: Fri Oct 08, 2021 11:37 pm    Post subject: Reply with quote

To me the problem with axial blade fans like that is that they tend to have low static pressure capability. The small flex duct in our cars has a very high pressure drop per foot and restricts the flow a lot. The new airfoil blade fans are much better than the stock style, but still not very good. A squirrel cage is a whole nother scale of static pressure capability. Before you go to all the work do that I 'd suggest finding a similar fan(old computer cooler or 2 maybe) install it into a cardboard box, Get a feel for the flow with some yarn attached to a stick, then put a top on the box take 2 or 3 pieces of flex duct out of the car attach them to the box and check again.

I spent a couple of years designing dust collector systems, a later avoided HVAC work whenever possible.
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924RACR  



Joined: 29 Jul 2001
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PostPosted: Sat Oct 09, 2021 2:37 am    Post subject: Reply with quote

Good points guys...

I think that while one of these radiator style fans may not reach the capability of a proper modern squirrel cage design, they still ought to have significant improvement over a 40-yr-old propeller design, with a more modern and efficient motor design and a more efficient fan blade, enough to significantly improve the effectiveness of the system in the vehicle.

More effort would yield an effective squirrel cage retrofit, but if we could get even 50% of the improvement for maybe 20% of the effort, that would be better enough for me!

I do have a squirrel cage motor and fan left over from my minivan (2010 Chrysler), which has a solid mounting plate... but the side of the cage seems like it should fit, if I flipped the fan element over... if I cut down the mounting base plate it seems like a plausible solution as well, and not very expensive. Still more work than a rad fan retrofit.

But I'm a bit of a ways away from doing this, as I first need to rebuild my Turbo motor (starting next week, finally)...
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Eliza  



Joined: 17 Aug 2015
Posts: 174
Location: Prov. Utrecht, The Netherlands

PostPosted: Sat Oct 09, 2021 3:03 pm    Post subject: Reply with quote

Thanks Morghen, that helps a lot!

I have found the fan I'll order for this. Here's the drawing:



This is 170mm including the cage and should, by the look of things, fit into the plastic housing where the stock fan lives. The "ears" might be hooked into the existing brackets if I cut them a centimeter or so from the outside, like so:



The fan draws 4,3 amps and has an output of 336 cfm ( 570 m3/h) at 0 static pressure. Does anybody have any specs at all for the stock fan? Would be great to have a comparison.

I admit, retail price for this is 75 EUR which is a bit steep, but compared to the 175 EUR the stock fan currently retails at, it's still a steal

Eliza
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