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Posted by: Larry Hubby Sep 19 2017, 12:19 AM

This has been one of those projects after which, when it’s finally done, you tell yourself that you would never have started it if you had known then how long it would take and what it would wind up costing. I know that there are plenty of you that know exactly what I mean. You all also know that it’s a lie, of course. You’d have done exactly the same thing anyway, but it’s a comforting thought that lets you avoid facing, if only temporarily, the seriousness of your 914 addiction.

Like many of you who have considered adding air conditioning to a car that hadn’t already been butchered by the typical dealer installation of one of the aftermarket units that were available when the cars were new, I was going to do everything right. No cutting gaping holes in the floor of the front trunk for the condenser, no modifying the firewall to clear the engine-mounted compressor, and no big ugly under dash evaporator unit that limits the occupants’ leg room. Did I achieve all this? No, but I did get further toward that goal than many others, and can at least cite what I think are solid reasons why I compromised where I did.

My car is a 1970 model and was originally a fairly base model 914-4. The only options it was delivered with were radio and chrome wheels. I bought it new in May of 1970 and have been working on it ever since. I used to jokingly say that I’d changed everything but the horn button, but I can’t say that anymore because I’ve changed that too. I drove it as a four for ten years and then converted it to a six in 1980-81 after I bought a ’78 911SC engine and transmission. At that time, all the necessary conversion parts were still available from Porsche, and the car consequently has nearly the same configuration as a factory six: motor and transmission mounts, engine tin, oil tank, heat exchangers, and even the electric windshield washer pump and steering column with its left-side ignition switch and lock. I wasn’t trying to counterfeit a six. It just didn’t make sense to re-invent the wheel when parts designed to do the job and guaranteed to fit and work perfectly were available so readily. As originality was never my thing, I’ve also replaced, slowly over the years, lots of things with better versions of the same thing from other Porsche models, such as five-bolt hubs and wheels, 911 parking brakes, 930 service brakes, 911 dash and gauges, 944 hydraulic clutch, 916 transmission, etc. But, as we all know, a factory air conditioner was never available for the 914, so there was no similarly easy way to adapt parts from other models that did have AC because you can’t just replace what isn’t there to begin with and you can’t in general add major things without significant modifications to the car. So, for some time, a rather long time, like 10-15 years, I’ve regarded a good integrated HVAC system as the most desirable addition to my car, and it’s taken most of that time for me to decide on a design and get it operational.

Here’s what the system I wound up with looks like from inside the car:



Note the lack of an under-dash evaporator, the two additional air outlets under the center of the dash, the electronic control module that replaces the stock fresh air control box, and the lack of a heater control lever on the floor near the gearshift. In the front trunk, things don’t look very different from stock, just an expansion valve peeking out from behind the gas tank and some small blowers, one where the windshield washer tank should be, betray modifications.



Both fresh air from the outside via the stock air intake at the center of the cowl and recirculated air from the passenger compartment are fed to the evaporator located under the cowl, replacing the stock air box, and the chilled air is then fed into the stock air distribution boxes and the two new outlets under the dash. For heat, fresh air drawn in through the engine grille in the back is blown, not by the engine cooling fan, but rather by only the stock 911SC engine-mounted electric heater blower into stock 914-6 heat exchangers (actually the Dansk reproductions), and then through the heater tubes inside the longs to the front trunk, where a pair of late 911 footwell blowers boost the air flow and feed the heated air into butterfly control valves, which replace the stock flapper boxes in the engine compartment, and then into the stock air distribution boxes. This arrangement provides heated air flow thru the stock vents which is independent of engine speed, while fresh or chilled air is available thru both the stock vents and the two supplemental outlets under the dash. Control over air distribution, heated air amount, and the introduction of fresh air is now electronic, accomplished via control motors mounted on each air distribution box, the heater butterfly valves, and a damper on the fresh air intake. This change was necessary because, believe it or not, there is no longer any room for the stock control cables! I was able to fit the electronics to run the control motors, the various blowers, and the AC into a package that fits into the same space as the stock item:



The knob on the left controls heating. Rotating it clockwise first turns on the three heater blowers, while further rotation progressively opens the heater butterfly valves. The set of five pushbuttons in the center do what the icons above them suggest, namely, turn outside air on or off, direct output air (for both heating and cooling), and enable or disable the AC. The knob with the fan icon controls the AC blower, and the knob on the far right regulates amount of cooling via a thermostat circuit that reads a thermistor buried amid the fins of the evaporator coil. The unit is removable from the front of the dash by loosening the two screws at the bottom corners of the front panel and pulling straight out.

Packaging the evaporator to fit in the space designed for the stock air box was accomplished largely by using a pair of Spal tube-axial fans instead of a centrifugal blower. These fans’ compact dimensions allow using a 911 evaporator coil in a vertical air flow configuration that simplifies routing the air from the external and recirculation sources to the stock air distribution system. The diagram below is a near-scale side cross-section of the evaporator along the center line of the car:



As you can see, the evaporator module just fits between the wiper motor and the gas tank, and I do mean JUST, but it does fit without modification to either. The length of the 911 evaporator coil (dimension in and out of the plane of the above drawing) also just fits within the length of the depression formed into the gas tank to clear the normal air box. This photo shows the under-cowl components installed, but prior to the re-installation of the gas tank:



I found it necessary to replace the stock windshield washer tank with a custom one that uses some of the space under the gas tank because the stock tank occupies the space where the passenger-side footwell blower needs to go. Here’s a photo of the tank before I installed it:



I made this unit largely from standard 2” ABS pipe and fittings, some flat ABS stock, a tank body that I made by building a plywood buck and then vacuum-forming ABS over it, and of course lots of ABS glue. The recess formed into the tank body is to clear the feed and return lines coming out of the bottom of the gas tank.

The fans I used in the evaporator are 5.1” units originally designed as radiator fans for ATVs, and, despite their compact size, they can move a lot of air, over 600cfm for the two of them. Unfortunately, this gets throttled down significantly by the rather tight ducting required to fit everything into the small space available under the cowl. Centrifugal blowers are normally preferred for auto HVAC applications for two reasons. First, because they’re quieter than tube-axial fans for the same air flow, and second, because their air flow falls off more slowly with increasing back pressure than does that of the tube-axial variety. The resulting air flow in this case, although down about a factor of six compared to what the fans will deliver in the open, is still significantly more than the output of the stock air box, but also still marginal overall in my opinion without the additional outlets under the dash that I added for just this reason. Somewhat more noise than a centrifugal blower might produce isn’t a major concern, at least not for me, because the 914 is not a quiet car. With a 3-liter six only inches behind my back, it can often be difficult to hear the radio, even without the AC blower running. It’s also my experience that I don’t tend to care about how noisy the blower is when I get in a car that’s been parked with the windows up on a hot day. Then I just want the AC to cool the car down as quickly as possible, noise be damned.

The other major AC system components, the compressor, condenser, and refrigerant lines are mounted in relatively conventional locations. I mounted a Sanden 505 compressor set up for r134a on the engine in close to the same location as the factory 911 compressor mounting, adding a jackshaft arrangement to the drive belts to step the compressor rearward enough to clear the firewall.



After installing the engine in the car and hooking up the hoses, it looks like this:



After considering several other locations, I finally mounted the condenser on the floor of the front trunk with air flow to it from openings in the front wall of the trunk and the bumper and flow out of it downward to exit under the car through a large reinforced rectangular hole in the floor of the trunk, concluding that, at least in my case, this is the only viable choice for a good-performing system.



The pressure and suction lines run from the engine compartment to the front trunk under the driver’s side rocker panel and the liquid line runs from the condenser in the front trunk to the evaporator box under the cowl following mostly the same route as the main wiring harness.

I’ve had the system operational now for a few weeks as of the date of this post, and it seems quite satisfactory. The measured air flow is very similar to that of my 2010 Honda Accord sedan, whereas the cabin volume of the 914 is roughly half that of the Honda, so the 914 cools down more quickly than does the Accord. I measured an exiting air temperature of 39°F on a 84°F day, which is in-line with what my other cars with factory AC systems will do.

I intend to post four additional threads, one on each major component of this system, to document the background leading to these choices, together with details of my construction efforts, for those who may be interested.

Posted by: djway Sep 19 2017, 12:49 AM

Very cool information. I have a car completely apart right now and I have been thinking long how to do near exactly the same thing. The air flow is exactly what I was thinking, I just had not figured it out yet, so no need to reinvent the wheel here . The footwell fans are a great idea. I look forward to your future post. I had also been thinking of adding power brakes

Posted by: db9146 Sep 19 2017, 05:40 AM

Cool! Add you'll start producing the kits by?????



Seriously, great job. Lots of research, ingenuity, engineering, and effort went into this, obviously. A nice, clean install with great results. I'm impressed! Wow.

Posted by: Cairo94507 Sep 19 2017, 06:57 AM

Amazing work. The older I get the more I want AC in my Six......

Posted by: mb911 Sep 19 2017, 07:10 AM

Thinking of looking at what they put in all electric cars.. Maybe a nice compact self contained setup?

Posted by: GeorgeRud Sep 19 2017, 07:57 AM

There's a fellow in England that has developed an all electric AC system for the 911 that looks like it may work for a 914-6. The advantage is being able to eliminate the engine driven compressor and instead use an electrical compressor (though it does require a fairly powerful alternator), thereby minimizing the AC line's long runs as well.

The jack shaft arrangement you've designed and the condenser/evaporator system looks great. I think putting AC in a -6 would make them much more user friendly as we age. I bought myself a 911 Targa to have at least one Porsche with AC to use on trips and keep a happy wife!

Posted by: Steve Sep 19 2017, 08:39 AM

Awesome!! Thanks for sharing!!

Posted by: 914Timo Sep 19 2017, 09:37 AM

Very nice Could we get more info/pics about power brakes too !?!?

Posted by: burton73 Sep 19 2017, 02:06 PM

This UK set up is more than $4,000 plus shipping.

Bob B

http://classicretrofit.com/products/electric-air-conditioning/

Posted by: amfab Sep 19 2017, 04:45 PM

Great solution and alternative to a big under dash eval!

Can you show some more detail of your condenser mounting construction?

Thank you

-Andrew

Posted by: horizontally-opposed Sep 19 2017, 05:47 PM

Gotta say that the UK setup—if it works—is very appealing even at $4k. A set of factory like heat exchangers is $3000~ without all the other stuff to go with them such as hoses and flappers, etc. And you don't get A/C. But you do get compromises in header sizing for some engines, more hot air kept close the cylinder heads, potential for "heat bleed" through the flappers on a hot day, potential for CO poisoning, etc.

$4k and no more heater boxes...and A/C?

I sent a note to the maker to get six conversions on their radar. How many are there now? Hundreds? More?

Posted by: mb911 Sep 19 2017, 05:52 PM

Hey stop it on the no need for heat exchangers as I am already behind my goal for heat exchanger sales..

Posted by: mepstein Sep 19 2017, 07:11 PM

I wouldn’t say heat exchangers are a done deal. Every car needs headers and adding heat just costs a little bit more and is still pretty much bolt on. But I do want at least one 914 with a/c.

Posted by: Dave_Darling Sep 19 2017, 07:57 PM

Where did you see no more heater boxes? I read that he is using the stock (repro) heater boxes, but instead of only using the engine cooling fan to push air through them he has the SC's electric fan only.

Totally awesome setup, BTW.

--DD

Posted by: horizontally-opposed Sep 19 2017, 08:47 PM

"INFO
The Electrocooler electric air conditioning installation for Porsche 911 is a complete heating and ventilation kit for the Porsche 911 models 1974 to 1989.

The kit is a total redesign of the 911 A/C system, with additional improvements to the fresh air blower unit and warm air distribution. It transforms the experience of travelling in an older Porsche 911…"



Read first line...now reading second line to see "warm air distribution" a little differently. System is still interesting, but a lot less so if it's $3-4k to get heating set up PLUS another $4k+ to get this system.

Good news for mb911 in that case, however…

Posted by: Racer Chris Sep 20 2017, 06:33 AM

+1

Posted by: Larry Hubby Sep 21 2017, 12:36 AM

Thanks for the kudos, guys.

914Timo and Racer Chris, I'll dig up some additional photos of my power brakes installation and post something soon.

Posted by: GeorgeRud Sep 21 2017, 08:55 PM

I think he still uses heat exchangers to provide the warm air, then uses his plenum to distribute the warm air. However, no one has actually driven and commented on the effectiveness of this system to my knowledge.