Heater Box
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Post by: carrierdave » Fri Jan 04, 2008 2:32 pm
Good afternoon all;
I have finally managed to remove the heater box and take one of the end covers off.
Please see the pictures below.
The air comes in via the fan ? you then have one damper blade sitting on top of the coil, this can be moved upwards to allow all of the air to go through the heater. As you come out of the coil there is another damper ? this allows the air to go into the car either via the bottom vents or back upwards towards the demister outlets.
On fresh air only the damper is closed across the coil and the air is circulated through to the smaller thin plenum where it can either travel out of the demist vents or if the bottom damper is open then it will travel downwards through the narrow plenum to the bottom vent. As the top fan plenum is pressurised, if you were to open one of the eyeball vents, air would travel down this path and reduce the airflow to the other outlets.
When it?s on warm you have the top flap partly between the coil and open to the narrow plenum. Therefore you have some air travelling down through the coil and some into the plenum.
However this will not work very well as there is little or no mixing of the air. If the coil is dirty then most of the cold air will travel through in to the plenum and exit vial the vents with the rest going through the coil ? if the bottom vent is open then all of the hot air will discharge at this point. If it is closed then it will eventually return up the narrow plenum to the demister vents ? however at a very small amount.
From what I can see there is no way you would ever get hot air from the eyeball vents as the takeoff for this is on the cold side of the coil at the discharge of the fan.
If you are trying to demist the windscreen the actual air flow is going to be quite poor. With the top and bottom dampers shut and the eyeball vents shut, the air will travel down through the coil and then return up the narrow passage to the demist vents ? This is a very narrow and tight route for the air to take and if there is insufficient external resistance on the fan it will stall.
All in all not one of the best designs going. Well now to the drawing board to see if I can improve things!!
Dave
ps - sorry you can not see the demist outlet only the eyeball one.
I have finally managed to remove the heater box and take one of the end covers off.
Please see the pictures below.
The air comes in via the fan ? you then have one damper blade sitting on top of the coil, this can be moved upwards to allow all of the air to go through the heater. As you come out of the coil there is another damper ? this allows the air to go into the car either via the bottom vents or back upwards towards the demister outlets.
On fresh air only the damper is closed across the coil and the air is circulated through to the smaller thin plenum where it can either travel out of the demist vents or if the bottom damper is open then it will travel downwards through the narrow plenum to the bottom vent. As the top fan plenum is pressurised, if you were to open one of the eyeball vents, air would travel down this path and reduce the airflow to the other outlets.
When it?s on warm you have the top flap partly between the coil and open to the narrow plenum. Therefore you have some air travelling down through the coil and some into the plenum.
However this will not work very well as there is little or no mixing of the air. If the coil is dirty then most of the cold air will travel through in to the plenum and exit vial the vents with the rest going through the coil ? if the bottom vent is open then all of the hot air will discharge at this point. If it is closed then it will eventually return up the narrow plenum to the demister vents ? however at a very small amount.
From what I can see there is no way you would ever get hot air from the eyeball vents as the takeoff for this is on the cold side of the coil at the discharge of the fan.
If you are trying to demist the windscreen the actual air flow is going to be quite poor. With the top and bottom dampers shut and the eyeball vents shut, the air will travel down through the coil and then return up the narrow passage to the demist vents ? This is a very narrow and tight route for the air to take and if there is insufficient external resistance on the fan it will stall.
All in all not one of the best designs going. Well now to the drawing board to see if I can improve things!!
Dave
ps - sorry you can not see the demist outlet only the eyeball one.
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Post by: john.p.clegg » Sat Jan 05, 2008 7:09 pm
Dave
Totally agree,you can get your legs nice and toasty,but as for any other function-a waste of space......let us know when you come up with any ideas...
John
Totally agree,you can get your legs nice and toasty,but as for any other function-a waste of space......let us know when you come up with any ideas...
John
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Post by: handi_andi » Tue Jan 22, 2008 7:38 pm
Ok have been thinking about this problem alot today, and my view is that the main problem is one of air flow and pressurising up the small phleum, as the whole point of it being smaller is to increase the air flow so as to demist the screen quicker. So is one possible solution not to replace the actually fan assembly with something a little more powerful using something akin to a Kenlowe radiator fan. I can not tell from the picture what side the fan itself is in diameter but Kenlowes go down to a 6" diameter (http://www.holden.co.uk/displayproduct. ... de=080.891) and there are smaller ones available for motorcycle applications (http://www.absoluteradiator.com/FanStore.asp?idDept=8). Might also make for a quiter running fan too LOL
The other problem I know I have on my own heater which I would think other people have too and will be interesting to hear what people have done to cure it, is that the flexible pipes up to the demister vents are exactly a good fit at the heater end and alot of air is being 'lost', which not only reduces air flow but stops the phleum pressurising up thus increase air flow rate.
Just some thoughts for shooting down or discussing.
Andy
The other problem I know I have on my own heater which I would think other people have too and will be interesting to hear what people have done to cure it, is that the flexible pipes up to the demister vents are exactly a good fit at the heater end and alot of air is being 'lost', which not only reduces air flow but stops the phleum pressurising up thus increase air flow rate.
Just some thoughts for shooting down or discussing.
Andy
Live life to the fullest - that's why I own a Lotus
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Post by: carrierdave » Tue Jan 22, 2008 10:08 pm
Hi Andy,
Yes you are correct in what you say. Installing a heavier fan with more external static pressure will overcome a lot of the problems.
There are however a lot of area?s of leakage. Unless you have taken the box apart and replaced them; the seals around the bottom plate/damper; and internal dampers perish and fall apart allowing air too leak out.
You are also correct, the connections from the plenum up to the demist vents are very poor along with the pipe connections to the eyeball vents ? unless these are closed you loose pressure to the demist vents.
Another bib problem for air flow in the air intake; when I took mine out you can see the problem. There is a hole in the bulk head to which they have glass fibred a circular ring ? this juts out into the air box. The actual gap around this (between the ring and the outer edge of the air box varies from 5mm to 10mm ? there is not enough free area to get sufficient air in.
One of the modifications I have done is to cut some of the ring back to give a greater area for the air inlet. I am also thinking of increasing the connection size for the demist vents and lowering the point at which the air is taken from. Its OK to have a small plenum to increase velocity but if it causes a back pressure greater than the fan can deliver you end up stalling the fan.
Dave
Yes you are correct in what you say. Installing a heavier fan with more external static pressure will overcome a lot of the problems.
There are however a lot of area?s of leakage. Unless you have taken the box apart and replaced them; the seals around the bottom plate/damper; and internal dampers perish and fall apart allowing air too leak out.
You are also correct, the connections from the plenum up to the demist vents are very poor along with the pipe connections to the eyeball vents ? unless these are closed you loose pressure to the demist vents.
Another bib problem for air flow in the air intake; when I took mine out you can see the problem. There is a hole in the bulk head to which they have glass fibred a circular ring ? this juts out into the air box. The actual gap around this (between the ring and the outer edge of the air box varies from 5mm to 10mm ? there is not enough free area to get sufficient air in.
One of the modifications I have done is to cut some of the ring back to give a greater area for the air inlet. I am also thinking of increasing the connection size for the demist vents and lowering the point at which the air is taken from. Its OK to have a small plenum to increase velocity but if it causes a back pressure greater than the fan can deliver you end up stalling the fan.
Dave
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