Ac from Classic Retrofit

Yellow · 10-05-2025, 03:17 PM

Hi, All
I purchased a partial AC kit from Classic Retrofit for my 74 911 restomod project. My car came with a dealer hack job ac installed. I demoed most, but kept the evaporator coil and blower located in the smugglers box. I have installed the kit (which is very nice) but I have not been able to get information on how to wire the kit to the blower. Has anyone installed a system like this? Would appreciate any advice.

mepstein · 10-05-2025, 03:39 PM

CR has all their tech and install manuals on their website.
https://classic-retrofit.com/forum/index.php?/forum/26-porsche-911-electric-air-conditioning/

Yellow · 10-05-2025, 04:06 PM

Thanks for reply…..I looked on their site…but cannot find what I need, and not being a teenager doesn’t help.

mepstein · 02:56 PM

Then you would just email or call Jonny.

SpyderMike · 10-06-2025, 09:27 AM

From my recollection, the blower is controlled through the blower switch as originally designed. The CR kit just adds a sensor wire to know if the blower is operating.

I did a partial CR kit and wired the power to the blower through an inexpensive motor speed controller from Amazon with a remote rheostat in the cockpit. I can provide those details if you want.

If you have the original AC switches you can just continue to use that. If you are uncertain how that was connected, I/someone can look up the schematic.

Yellow · 10-06-2025, 01:24 PM

SpyderMike,
Thanks for your response. I don’t have any AC switches and am uncertain how the blower was controlled. I would like to control the blower with factory fan switch, but not sure how to do that.
I would be interested in your details of your installation and where you connected the sensor wire.

SpyderMike · 10-06-2025, 06:37 PM

Without knowing what you have exactly, I need to talk in generalities. Do you have the factory switches then? Basically, power will go from fuse panel through switch to the blower. On the CR side there is an orange blower sense wire that you connect to the blower power line coming out of the switch.

Do you see that orange wire in you loom coming out of black loom from the CR ECU to the on/off switch seen here?

Yellow · 10-07-2025, 06:26 AM

I have those same drawings, but what wire on the blower does it connect to? And how would that work with the blower in the smugglers box? I’m not going to use the factory fresh air blower for heat, can the two blowers be controlled by the fan switch and how could they be wired?

SpyderMike · 12:42 PM

Quote:

Originally Posted by Yellow

I have those same drawings, but what wire on the blower does it connect to? And how would that work with the blower in the smugglers box? I’m not going to use the factory fresh air blower for heat, can the two blowers be controlled by the fan switch and how could they be wired?

It connects to the blower power wire so that it knows when the blower is on. You can connect to the blower power line anywhere along it. I have the variable motor controller (less than $25 on A) and I have both the sense wire and the blower power wire connected together on the power output side, for example.

I am not sure why you would want the fresh air and cold air blowing at the same time, but you would want to determine the combined current draw of the blowers and the current rating of the switch and the wiring in between. If the draw is comfortably withing the rated limits, then yes. If it is over the rated limit, then a relay setup could be created.

Yellow · 10-07-2025, 05:22 PM

I was thinking of connecting a duct to the fresh air system to help with the AC distribution but not sure know. So you use the variable controller to turn the air conditioning on. Is it mounted on the dash? Does it match with the other knobs ?
For your AC blower….where are you getting the power from? Can the fuse used for the fresh air be used or should I use a separate one?

SpyderMike · 10-08-2025, 09:42 AM

The motor controller is in the front trunk area...the rheostat is in the cockpit. The rheostat could potentially have any number of different knobs put on it...they just slide on. During my car backdate project I rewired most of it and came up with my own scheme. I have a separate small fuse block for the AC needs that is fed off the battery.

If there had previously been an AC system in your car, are there any remnants of the wiring at or near the fuse panel?

You can see what I did here:

https://forums.pelicanparts.com/porsche-911-technical-forum/1144750-1985-ac-project.html

SpyderMike · 10-08-2025, 09:44 AM

By the way, the Griffiths blower upgrade blows great. With that upgrade and additional venting, no other blower is needed in my opinion. I have yet to run it at full speed. Something to consider...

Jonny H · 01:36 PM

Our kits do not control the blower as that is done by the factory controls already in the car. The only connection is to 'detect' blower on which is the orange wire.

Bottom of page:

https://classic-retrofit.com/forum/index.php?/topic/1235-07-cabin-controls/#comment-1864

"For those using our half kit, you do not have to install our cabin button. You can use the factory blower switch to turn on the AC. This requires wiring the orange wire in our loom to the red/white wire on the factory blower 4 pin connector.

Installation of the half kit requires changing settings in the ECU. "

The ECU settings that need changing relate to the orange sense wire ( which detects the blower fan being on ). This is documented here:

https://classic-retrofit.com/forum/index.php?/topic/2472-blower-sense-voltage-what-does-the-orange-wire-do/#comment-4057

See main text for ECU settings and note the 'Automatic Compressor On with Blower" mode

Yellow · 10-08-2025, 03:41 PM

SpyderMike,
I want to thank you for your advice, and your journey through your process…..I now know how you came up with Spyder Mike.
Jonny H,
Thanks for your input. The AC system that was left in the car when I purchased consisted of the VW Ccccool evaporator and blower in smugglers box. No controls are to be found…..I would like to keep your cabin button to show system status…..but if I connect the orange wire to the factory fresh air blower….how will it connect to the AC blower? If you could provide a sketch, it would be greatly appreciated. By the way…just installed your new fuse block….that’s a thing of beauty.

Jonny H · 10-09-2025, 12:00 PM

Hi Yellow,

When you have a smuggler's box evaporator/blower, the fresh air blower and sliders have nothing to do with the AC in a 911.

The evaporator AC blower would normally have a separate rotary switch on the centre console to control it.

You only need to connect the orange wire to the AC blower. I would suggest you get the AC blower motor working with a rotary switch of your choice.

One of the wires to the switch will show a varying voltage depending on blower speed but this depends whether it is wired to switch the 12v (high side) or the GND (low side)

Read second link above to understand the difference between high and low side switching. That will govern where to connect the orange wire.

SpyderMike · 10-09-2025, 12:32 PM

I found this thread interesting - it might help you understand how your original system was put together:

https://www.912bbs.org/forum/threads/912e-air-conditioning-components-upgade.56213/

Post 15 shows the system installation instructions!

mikedsilva · 10-09-2025, 01:09 PM

Does their system support heating as well as cooling yet? I'm waiting for that to happen, before investing.

Jonny H · 10-09-2025, 02:14 PM

^ Heat pump release (ac + heat) Q1 next year we hope!

Brookieslayer · 10-09-2025, 09:31 PM

Quote:

Originally Posted by Jonny H

^ Heat pump release (ac + heat) Q1 next year we hope!

Great News Jonny!

Yellow · 10-10-2025, 03:48 PM

SpyderMike ….thanks for your help. I found that original installation instructions on the 912 forum, and that explains a lot. I will follow your and Jonny’s advice and install a rotary switch in the dashboard, my car does not have a console. It will be a while before I can test the system…have a lot more work before the car is complete.
Thanks again guys.