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Lars S
Samba Member
Joined: October 04, 2007
Posts: 817
Location: Sweden
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 Posted: Thu Dec 03, 2015 11:56 am Post subject: Why double heat control boxes? |
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Why is there a need of a second heat control box on each side in the heated air system in addition to those at the heat exchangers? The ones i mean are located under the car where the air tubing enters the cabin (pictured).
I expect the ones at the heat exchangers to be there since those are to be found also at type 1 and 3's and I assume the others are there because the gas heater is in the same system on the Type4 but I cant understand why.
Wery early cars do not seem to have the extra heat boxes.
/Lars S
_________________
Porsche 914 -72, Bahia Red daily driver 
VW411 2-d -70, White, sold 
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23111
Location: Oklahoma City
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| Posted: Thu Dec 03, 2015 1:13 pm Post subject: Re: Why double heat control boxes? |
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As far as I have found.....all of my cars....have only had the single heater control boxes mounted on the body/heater channel entrances. There have been on my cars....no heat exchanger mounted heater boxes or upper heater boxes.
The path on my cars has been....heat exchangers to un-insulated hoses....to gas furnace inlets....from gas furnace out lets......to insulated hoses.....to the chassis inlet heater control boxes. Ray |
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Pelle
Samba Member
Joined: February 07, 2004
Posts: 214
Location: Sweden
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| Posted: Thu Dec 03, 2015 2:54 pm Post subject: Re: Why double heat control boxes? |
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| The ones at the heater boxes are only mounted on cars with M202 (improved heating). Typically found on Swedish cars 72-74. Cars with regular heating doesn´t have aluminum flanges in the heater boxes. The larger heater box probably produces more heat than what the Eberspächer likes. |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 23111
Location: Oklahoma City
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| Posted: Thu Dec 03, 2015 5:13 pm Post subject: Re: Why double heat control boxes? |
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| Pelle wrote: |
| The ones at the heater boxes are only mounted on cars with M202 (improved heating). Typically found on Swedish cars 72-74. Cars with regular heating doesn´t have aluminum flanges in the heater boxes. The larger heater box probably produces more heat than what the Eberspächer likes. |
Pelle....I am not close to my parts book. Is M202 the front trunk mounted gas heater unit? Ray |
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Lars S
Samba Member
Joined: October 04, 2007
Posts: 817
Location: Sweden
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| Posted: Thu Dec 03, 2015 10:39 pm Post subject: Re: Why double heat control boxes? |
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| Pelle wrote: |
| The ones at the heater boxes are only mounted on cars with M202 (improved heating). Typically found on Swedish cars 72-74. Cars with regular heating doesn´t have aluminum flanges in the heater boxes. The larger heater box probably produces more heat than what the Eberspächer likes. |
Thanks Pelle, I did not know that!
M202 should be the fatter heat exchangers which were available '72 on (I thought they were fitted on all cars after '72 but apparently not).
The wires from the right heat lever between the front seats is connected to the front control boxes only. Then there is another set of wires from the front control boxes to those at the heat exchangers. Thats why the control arm on the front box looks as it does (pic below): a wire is to be connected at each end of the arm.
Also note that these front boxes does not dump the air to outside when closed, only the boxes at the heat exchangers does.
Lars S
EDIT: As to why there are needed still a little confused, I would have thought that the gas heater could stand wery high temps but maybe the air can get so wery hot that the high temp switch in the gas heater will cut out.
The rear control boxes dump the hot air to outside when closed so not much air should go into the gas heater then (if everything is adjusted and working OK). By adding the front pair of control boxes the risk for hot air entering the gas heater is reduced but the system is also getting further complicated.
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold |
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