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Join Date: Jan 2002
Location: Austin, TX
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AC Upgrade for 1986 Carrera

What started out as replacing the AC hoses and rebuilding the compressor on my 86 Carrera turned into a complete overhaul and redesign. Of course the first place I turned was this forum. There is plenty of great and entertaining discussion on the subject which I distilled down to three options: 1) Do nothing. 2) Get a killer, and $$$$ set-up from Griffiths or Retroair. 3) Refresh and improve the existing system. I chose # 3. Mainly for the challenge and to save money. Usually this approach increases cost as I end up redoing it the expensive way eventually. This time might be different.

I went the wwest direction by replacing the rear condenser with a modern parallel flow condenser and two fans. However with the added twist of eliminating the front condenser and associated plumbing and adding a second condenser in the rear. I’ve read the parallel flow condensers, PFC’s, are 25% to 40% more efficient. I have no data on efficiency of the fans add but my guess is it’s moderate to substantial.

In short, the redesigned system is as follows:

Rebuild existing Nippondenso compressor. $ 210
New hoses. $ 325
Replace OE rear condenser with a 12” x 26” PFC and OE front condenser with a 11” x 20” PFC sandwiched together in the tail. $ 187
Add dual 6” fan kit, with shrouds. $ 79
Trinary switch and adapter to manage the compressor and turn on the fans. $ 50
Replace expansion valve and pressure test evaporator. $ 60
I used the Porsche Technical Service Bulletin for R134 Conversion as a guide for oil and freon capacity.
5 oz oil and 36 oz freon. $ 30
I’ve calculated that the combined PFC’s are 22% larger than OE. Considering 25% to 40% better efficiency of the PFC’s I estimate what I’m calling an “increase in condenser function” of 50% to 70%. This before fans are factored in.

All in $ 862.

Note - My car has a factory tail, automatic heat blower for overheat protection and is the first year of the “large vents”. It had not been converted to R134.

Note - The system wouldn’t turn on at all with the front condenser blower disconnected. Apparently the system needs that fan running to function. I plan to install a 6” fan on the right fender oil cooler and connect it to the existing condenser fan plug. Any input on this will be appreciated.

I sourced everything locally except the dual fan kit which I got from Amazon. Certainly you can find everything cheaper by shopping the internet but I chose to support my local business, Austin Rebuilders.

I finished up last night and gave it a test drive of about 12 miles. The ambient temp was 86 degrees outside of Austin, TX and lowest observed vent temp was 37 degrees. Idle/stationary temps were mid to upper 40’s. I feel like the system needs 5 to 7 more ounces of freon which I will add in the next few days.

I "WWested" my 84's a/c system

A "quick" AC condenser question

https://www.pff.de/wcf/index.php?attachment/305822-retrofitting-r134a-a-c-1995-680195-pdf/

https://www.amazon.com/dp/B01I0V12CU/ref=sspa_dk_detail_7?pd_rd_i=B01I0V13DS&pd_rd_w=dBC5g&pf_rd_p=8a8f3917-7900-4ce8-ad90-adf0d53c0985&pd_rd_wg=wuHQM&pf_rd_r=67ANV0V9QN3KTAGWSYTC&pd_rd_r=e18e303d-9a94-11e9-ba83-dbb3b2ee441e&th=1

AC Source - Automotive Air Conditioning, AC Parts Tools Equipment Kits

https://coldhose.com/parallel-flow-condensers.html

12" High x 26" Wide Air Conditioning Condenser

https://nostalgicac.com/parallel-flow-condensers/painted-condenser.html



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1973 911T Sepia Brown MFI
1986 Carrera Meteor Gray Metallic

Last edited by Steve Marshall; 06-29-2019 at 10:37 AM..
Old 06-28-2019, 02:07 PM
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Please don’t take this personally but the sandwiched condensers are a waste of time.

When we developed our system, we had a condenser company run thermal load calculations on various configurations. This showed that if you sandwich two condensers together, you get no measurable difference in heat load performance over a single unit.

This is down to two reasons.

1). The first condenser pre heats the air to the second. The second struggles to cope with the extra heat.

2). Using two condensers restricts the air flow which reduces the efficiency of both.
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Last edited by Jonny H; 06-30-2019 at 11:54 PM..
Old 06-28-2019, 02:24 PM
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That's an interesting theory and actually something I was concerned about. However the Griffiths and Zimm's fender condensers basically sit adjacent to the catalytic converter and they get rave reviews. Fresh air off the tail has to be much cooler? So for the cost of 2 common condensers at $ 187 total I decided just to go for it. Apparently the fans provide enough air flow to overcome any air flow restrictions or preheat condition. They are set to turn on 220 psi and the pressures stay within the standard operating range for the ambient conditions. Worst case I'm achieving the low end of my 50 to 70 % increased effectiveness (not counting fan effect). However I'm still tweaking and gathering data. I'll be sure to report back. So far I'm encouraged. I don't think there's room to sandwich condensers on cars without tails so I'm surprised you even considered that as an option when designing your system?
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1973 911T Sepia Brown MFI
1986 Carrera Meteor Gray Metallic

Last edited by Steve Marshall; 06-29-2019 at 09:52 AM..
Old 06-28-2019, 03:13 PM
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^. We use a single Boxster condenser at the front of the car (under the headlight).

We considered sandwiching two Boxster condensers but the thermal calcs showed this to be of no benefit. The calcs were done for us by a major condenser manufacturer.
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Old 06-28-2019, 03:26 PM
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Steve,
Very interested in how your setup runs doing our 90deg days along with oil temps. I’m still needing to get on my list of projects and run wiring and install fan on my setup.

Just this past Sat I was up at GT Intl and on way home ran the AC with windows down since it couldn’t keep me cool. After sitting in traffic and a drive through I saw oil temps just shy of 250deg. Curious of your oil temps while running your AC setup.


CTopher
Old 06-28-2019, 04:59 PM
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CTopher,

I haven't had the opportunity to collect data above 85 degrees. On initial start up it was idling for an hour while adding freon and buttoning up. The deck lid was open so no additive cooling from the condenser fans hit the engine. Engine temp was 2/3's hot and the heater blower fan in the engine bay kicked on. As soon as I took it out for a drive engine temp settled at the half way point. I'm concerned about engine temps as we all are down here so I'm keeping a close eye on that and will report back. I feel like adding a fan to the front oil cooler will build in an added level of cooling for the hot Austin stop and go traffic.

FYI - I read the gauge as 1/3 hot, 2/3 hot and too effing hot! Not sure what the actual temps are!
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1973 911T Sepia Brown MFI
1986 Carrera Meteor Gray Metallic

Last edited by Steve Marshall; 06-28-2019 at 06:46 PM..
Old 06-28-2019, 06:41 PM
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Old 06-28-2019, 07:25 PM
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I collected more data today. Ambient temp 85, road temp 100.

Ran the car stationary in my barn at 2,000 RPM for about 10 minutes and got to a vent temp of 34. (I think this is too low and might have been caused by the thermal probe being inserted only half way into the evaporator). My throttle man expressed that it was "unbearably cold".

Checked the inlet and outlet temps of the sandwiched condensers. 219 coming in. 125 coming out. I have no clue what they should be. The IR thermometer was bouncing around between 200 and 230 and 100 and 135. The pictures below happened to be what it was reading at the time I took the pic. I figure the delta is what matters and that remained consistent.

Pressure readings were 13 on the low, 275 on the high. The high side pressure is a little high for the ambient temp. I might have an ounce or two too much R134 in there.

I drove 8 miles into to town and the vent temp settled at 41.

Sat with car idling in a hot parking lot for 10 minutes and the vent temp rose to 51.

Drove back to barn and vent temp settled back at 41.

Friday I drove my 2018 Buick Regal Tourx around Austin with the thermometer shoved in the vent, just to see what temps a modern car produces, and it was between 43 and 45 all day. 85 was reading in the dash and I'd guess the road was 100.

This is by far the coolest summer in Austin in years. I'm really curious how this will perform on 95 to 100 degree day which is more typical for this time of year.

Sitting in the barn for 10 minutes at 2,000 RPM

Entering the condensers.

Exiting the condensers.

On the road.

In the parking lot for idling for 10 minutes.


I have no clue why the pics are sideways. I promise I didn't do into annoy! They were not taken that way and only turn on their side when I post them here.
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1973 911T Sepia Brown MFI
1986 Carrera Meteor Gray Metallic

Last edited by Steve Marshall; 07-01-2019 at 11:15 AM..
Old 06-30-2019, 07:21 PM
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^. I thought that post was clear but perhaps not. ‘No measurable difference’ between a single condenser or two condensers sandwiched together. I have edited the post for clarification.

All I’m saying is that your setup would work just as well with the single unit. It would be interesting to measure the outlet of the first unit as well.
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Old 06-30-2019, 11:58 PM
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Jonny H - Thanks for clarifying. I probably misunderstood your post as well. If you're correct then one condenser should do it based on the results? I'm curious what the temps are on single condensers? Do you have temp data on your systems? I'm going to check a few modern vehicles I have just out of curiosity.
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Old 07-01-2019, 11:09 AM
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I live in Miami, my car has a single modern condenser with two fans in the rear and handles 90 degree no problem. Its an SC
Old 07-01-2019, 12:56 PM
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Quote:
Originally Posted by Ryce Stallings View Post
I live in Miami, my car has a single modern condenser with two fans in the rear and handles 90 degree no problem. Its an SC
By "modern" condenser, do you mean PFC? If so, from whom did you buy it if you don't mind me asking?
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Old 07-01-2019, 01:28 PM
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My car has a proprietary system, I will ask the installer where the condenser came from. I do believe its a Parallel Flow type. My system does not use a blower in the smugglers box it has larger evaporator coil that moves more air. Ive had other systems in my car over the years, this one stays cold in Miami weather.
Old 07-01-2019, 03:30 PM
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So after a few iterations in the last six weeks I was able load test the AC last weekend. The ambient temp ranged from 100 to 104 and traffic conditions ranged from stop and go, to none. The vent temps stayed between 44 and 55 and this was perfectly comfortable. In ambient temps of 95 or below the vent temps hover between 39 and 50.

Through this effort I realized there are 3 system factors that are really critical to a properly functioning AC that must be addressed or you'll never get it right. 1) Amount of freon in the system. It takes exactly 39 ounces of R134. If you're unsure how much you've got in there, be under 39oz. I was over by 2oz and and the result was a 4 degree increase in the vent temp. 2) Properly placing the thermostat probe in the evaporator. 3) Finding thermostat 32 tick on the dial. Not that important at 104 but very important under about 92. You'll be chasing freeze ups until 2 and 3 are resolved.

So in the end I bought a Griffiths front condenser. This is an excellent product and bolts right in. I also added 12" x 16" parallel flow condenser and 12" fan to the front of the left rear fender. I feel like bang for buck this made the biggest improvement, save for the correct amount of R134.

If I had to do my sandwiched tail condenser set up over again, I would go with just one large condenser and get as much fan in there as I could. I've redone the AC on my 91 Vanagon also and as the with the 911, air flow across the condensers is huge. The parallel flow condensers are also a very big improvement over the old style.


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Old 08-14-2019, 11:28 AM
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Great post! Similar weather up north in Dallas. Do you mind telling where you sourced the PFC for the rear fender and how you went about mounting it? I'm about to attempt the same.

Also it sounds like you completely eliminated the tail condenser, right? So only the left rear fender and factory front condensers running now? Final charge for that two condenser set up was 39 oz.

Thanks!
Old 08-14-2019, 11:42 AM
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Got the PFC and 12" fan off Amazon. $ 50 and $ 40 if I recall correctly.

I did the opposite on the tail. I stuffed two condensers sandwiched together in the there with a couple 7" fans. The jury is still out on whether sandwiching two condensers works or not. I have to figure it's at least marginally better but the cost was minimal. I took out the front condenser and all the plumbing but eventually added them back in.

I fabricated the rear condenser mounting and shield from some left over material a buddy used to protect the radiators on his dual sport motorcycles. The basic set up is fab a bracket that bolts to the torsion bar hole cover stud and use a self tapping screw to attach the dog ear at the top of the bracket to the inner fender well. If I recall, the top of the condenser is positioned outside of the trunk pull hard pipe.

I've been all over the place with the freon amount. I thought the number of condensers would have an effect. Apparently it doesn't. Griffiths uses 39oz with their 4 condenser set up. My experience is that you can get cold air with 30oz but the system doesn't keep up over time.
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Last edited by Steve Marshall; 08-14-2019 at 12:11 PM..
Old 08-14-2019, 11:58 AM
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Hey, if it work in Austin, TX on a 100+ day in traffic you should be good to go. Did you see an increase in oil temps by dumping the extra heat into the engine?

10 years ago when I upgraded my system I did not want to invent the wheel. I went with the full Griffith system. 4 condensers total, the two new ones in the fender, I still have the original condensers front and rear. I just drove down to Key West with my brother. Two um, "full size" adult men and we laughed about our glasses fogged up from ice cold air blowing on our faces and getting out of the car into the Florida humidity and 95+ heat. My engine temps never got above 210. Even in rush hour traffic going 5 MPH.

I drove home across 1-40 through Memphis, TN to Oklahoma City. 95+ degree heat 85% humidity with the sun shining in my face and on my chest. I had to divert the air from blowing directly on my face because it was uncomfortably cold. I diverted the air to my body and the cabin. It was a an 11 hour drive starting in Montgomery, AL to OKC, in July. I was totally comfortable on the entire trip. I had to park in the full sun, and stop to eat, and get gas. The HOT engine soaked the AC system. Within two minutes, I was comfortable after getting back on the road.

Next year I drive to Palm Springs, CA in June. That will be another hard test for the AC system.
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Old 08-14-2019, 12:32 PM
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GH85 - That's some serious AC stress tests you've put your system through. I've not road tripped yet and I'm curious how performance will be over time.

Throughout his AC adventure I would stop in a parking lot and idle for 10 minutes to see how hot the engine got. It never exceeded 2/3's hot when the ambient was in the mid 90's. Which is about as hot as it got before I started messing with the AC. This didn't concern me at all but I decided to add a 7" fan to the oil cooler just to be safe. It's a cheap and easy upgrade. It's not connected to a thermostat it but it is wired to run only when the AC is on. I figure if I'm not not running the AC, it's not hot enough to need the extra cooling.

It's hard to tell for sure, but I'd say with the addition of the fan the temp now stays between 10 to 15 degrees below 2/3's hot.

I'm not convinced fans on the condenser are an engine heat issue. I can see in how in theory it might be? Maybe? Kinda? But in reality I'm not experiencing it. How can more airflow at idle hurt?


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Old 08-14-2019, 01:47 PM
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Wow Steve, glad to see someone having success doing this. Did you do the evacuation yourself or did you have an "AC" shop do this part of the project?
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Old 08-14-2019, 07:36 PM
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The system had no freon when I started. Once I assembled everything I vacuumed the system for a couple hours, let it stand for a couple more to see if I had any leaks and then filled with R134.
Old 08-15-2019, 08:01 AM
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