A/C air flow mods

[jeffc280sl]

I've started cleaning up the A/C system since is off the car.  Took a look at the evaporator box and air flow dead ends and obstructions.  I'v attached some pictures of some proposed changes and I'd like to hear some opinions from the group.  The vent at the right of the front panel is directly in front of the blower fans and as such it gets the most volume.  There is a small flat deflector baffle installed in the top plate that is supposed to reduce air flow to this vent.  While it does accomplish some reduction I think it creates turbulence in the air flow and has air currents bouncing against each other which is inefficient.  I've mocked up a diverter of sorts that is curved.  There is an opening for the right side vent and I hope the balance of the sir flow is doirected to the left side of the front panel.  The curve eliminates "dead" air which may be trapped in the right corner of the fromt panel.  I made a similar mod to the left side to divert the flow out the front panel and reduce turbulence in that dead space.  In the center of the box I bent a small piece of the evaporator box.  This simple mod increases the air flow at the choke point where cool air leaves the evaporator box and heads to the center and left duct openings.  This small change increases the area for air flow by about 25%.  Ordered a new motor today so I can't run an air flow test.

Any thoughts?

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Jeff C.
1970 280SL 4-speed

[George Des]

Jeff,

This just might work as far as directing the air stream more towards the driver's side which is a real deficiency in the original design to begin with. My guess is that when the designers were looking at how to best cool the cockpit they first consdiered how small a space actually needed to be cooled. The original design is more than ample in this regard provided it is used with the hardtop. I suspect, though like me and many others, we've all gotten used to the modern a/c systems that are such powerhouses that they they can even make traveling down the road in an open convertible on a hot, humid day bareable.   I know Tom Sargent had his a/c system modified by Gernold in such a way that the air flow is alos more directed towards the driver. As I recall he used some sort of adittional ducting and internal baffling to do this. I believe Tom form Boise has done the same. I have not done this myself, but have followed suit with Tom S and installed a new, 3-speed, high volume blower assembly to the stock evaporator box.

George Des

[jeffc280sl]

George,

Can you tell me what blower assy you purchased.  Same for the motor if available.  It would be great if you had specs for the motor like hp and rpms.

Thanks

Jeff C.
1970 280SL 4-speed

[George Des]

Jeff--check out this SPAL website <http://www.spal-usa.com/>. I'll have to dig through my stuff to retrieve which of the assemblies I've got, but it is a direct fit to the stock evaporator box. I have a Kuhlmeister and I did have to relocate the condensate drainage tube from the back of the box to the bottom in order to gain some clearance--others with the Frigiking said they did not have to do this. If you do a search on the site you may find the post where one of the Tom's gave me the correct SPAL number as well.

George Des

[George Des]

Jeff--I just checked my link--if you remove that last >, it should work.

[AGT]

Jeff

I fitted the SPAL blower which George recommends. It is a very powerful three speed unit which transforms the output from a feeble puff to a torrent. With the FrigiKing, the blower fits right up to the evaporator box with no modification needed. It does take up a little more footwell space right at the back and it was a bit of a struggle to squeeze the carpet back under.

I don't have the SPAL unit number in my papers for my new a/c components and could not find it on this site. My unit was supplied earlier this year through Gernold at SL Tech. I am sure that he will give you the part number if you ask.

With the power of the SPAL blower I don't think that much needs to be done to re-route airflow from the FrigiKing underdash unit unless you normally travel with a passenger who will be deep frozen to maintain a comfortable temperature for the driver.

Regards
Andrew

[jeffc280sl]

Thanks for your comments.  I've decided to suspend the main baffel from the top cover plate of the evaporator box.  This way I don't have to drill holes in the base which may leak from condensation.  I understand a more powerfull blower will force more air through the duct openings.  In the factory design it means even more turbulence.  Maybe these mods will allow the fan to run at a lower speed making it more quiet. In the corners I may use some of that blow in place foam insulation.  The fan motor I purchased yesterday is 1/8 hp, 3 speed, 4200 rpm max.

Jeff C.
1970 280SL 4-speed

[George Davis]

Jeff, I suggest something like this.  The idea is to actually segregate the airflow into two sections, forcing more to the left end vent.  The position of end A determines the split.



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George Davis
'69 280 SL Euro manual

[jeffc280sl]

George,

Thank you for your idea.  I've attached an edited version of your drawing.  It's a little more representative of scale but not exact by any means.  As you know i've cut an opening in the main baffle to feed the right side vent.  There is a big choke point at the start of the second vent.  This is where things really skinny down.  This is why I removed the tab.

Thanks again

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Jeff C.
1970 280SL 4-speed

[jeffc280sl]

Here are some additional pictures.  The baffle is mounted to the top of the evaporator box.  Once duct insulation is fixed to the bottom of the bow the baffle will fit snuggly.  The rectangular cut out in the front is for the right side vent.  The extra diverter on the right side is there to force air out the vent so it does not get "stuck" in the front right corner of the A/C front panel.  A similar baffle is attached to the left side so that air does not get "stuck" in the left corner.  I'll let everyone know how it works out when the new motor arrives next week.

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Jeff C.
1970 280SL 4-speed

[jeffc280sl]

Received the new blower motor today.  Cost around $55.00 so that part was good.  Had to swap a couple of wires to get the 3 speed switch function to work correctly but that was easy.  This is simply a replacement motor that uses the old squirl cage fans and fan box.  Have not put the evaporator in the box as yet.  Will do that in the next few days. Baffle mods worked okay.  After choking down the baffle opening feed to the right vent I was able to get very even flow between the right and left vent. The baffle opening for the right vent is about 2 to 2-1/2 sq in.  The center vent has about 1/2 of the air flow of the right and left vents .  The blower air just rushes right by the center vent.  I'm going to leave as is and proceed with the balance of the new A/C system.

Jeff C.
1970 280SL 4-speed

[doitwright]

Jeff,

How have things worked out with your A/C duct modifications.  I am looking into doing something similar since I am in the process of replacing my interior.  Any other tips on your experience with this upgrade?  Did you change to a rotary compressor?  How has this effected engine temp?

Frank Koronkiewicz

1970 280SL Light Ivory
1972 911 Targa

[jeffc280sl]

Hi Frank,

The A/C project is not a high priority task for me so little additional progress has been made. Too much fun driving the SL in the spring time to lay it up in the garage for repairs/upgrades. I'm looking at the overall cooling system as apparently you are.  As a first step I've upgraded the altenator to a larger capacity unit and right now I'm looking at installing electric fans in place of the mechanical fan.  Once that is complete I will get back to the A/C system.  I plan on adding a rotory compressor and a hi capacity condensor.

Jeff C.
1970 280SL 4-speed