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Classic Retrofit A/C Experience & Guide
NOTE SOME PEOPLE ARE SEEING SOME OF THE PICTURES UPSIDE-DOWN. Let me know if that is the case. On my systems they all seem to be correct.
Disclaimers This is a long one, sorry. It just kept growing and growing. I am by no means an expert, just wanted to pass along what I learned.BLUF (Bottom Line Up Front I loved the idea of the CR A/C before I bought it and knew my particular case would be a tough installation. I also knew my climate would be about the toughest there is for an A/C system given the heat and humidity we have here. Throughout my install CR have been very supportive and helpful, even when I screwed things up myself. I did that at times, royally to be sure. They were wonderfully patient and positive.My Goals for this writeup To provide people looking into, or who have the Classic Retrofit A/C system some guidance on getting the install & settings right, and the benefit of my testing and experience.My A/C Setting Theory In a heat-soaked car I want to cool the car as fast as possible and get it to my desired temp ASAP. Many modern A/C systems (like my 2012 BMW X5) start to back off well above the set temp, and therefor never really get to the set temp. In my X5 I have to lower the temp below where I want it, then once the car gets close to how I want it to feel I move the temp setting back up to let the car back off and keep the car cool. This is rather annoying in a hot and humid climate. My desire was to have the system “cold crash” the car as fast as possible, and not back off until right before the set temp, while still giving the system enough resolution to back off without over cooling the car. I think I have achieved that, though come cooler fall weather I may need to make some minor adjustments. Time will tell.A/C Things to Know. I have proven this system has the capacity to handle very hot and very humid climates. When an A/C system runs out of capacity the condenser output temperature rises well above the ambient air temp. Conversely in a properly running system the output fitting on the condenser is near ambient at all times, once the system has stabilized. CR and I occasionally talked about the possibility of adding a second condenser to the system to help with my really hot & humid climate. To-date though my condenser output has never been more than 3C above ambient (using my IR Gun), and that includes on 100+F days with 40%+ humidity.
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles Last edited by Duc Hunter; 06-03-2019 at 01:44 PM.. |
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These A/C systems will see similar low pressures to a traditional belt driven compressor system. They will not see the same high sides though, at all. The chart below is a typical R134 ambient temp-to-pressure chart. I have never seen my high side pressure much above 170PSI, and my low sides, once the system has stabilized, are slightly below these. Also remember the evaporator’s temp is typically about what your low side pressure is. Notice the PSI of 50-55PSI at 38C/100F outside air temp? This means any R134 systems evaporator is “supposed to be” about 50-55F, or 10-12.8C, in that weather. This means, in theory, no R134 system can get near 4.4C/40F degree vent temps in 38C/100F outside temps. R134 is not as efficient/cold as R12 was, and yet R134 cars still cool off just fine. Just keep this in mind.My Systems Performance Living in Florida we have massive heat and humidity. In one test where it was 40-42C on my outside airtime gauge throughout the test, I got into a heat-soaked car where the evap temp was 41C (105.8F), the center vent temp was 51.4C(124.5F) when I started the system. Can we say STEAMY? 5 minutes in the evap was 9.5C(49.1F) and the vent was 15.5C(59.9F) and the car was comfortable (not cold, but comfortable). 10 minutes in the evap was 6.8C(44.2F) and the center vent was 13.5C(56.3F) and the car was comfortable. 15 minutes in the evap was 5.5C(41.9F), the center vent was 10.6C(51.1F), and the car was very comfortable. The whole time the system was on high blower speed and all of the vents were open. This outperforms the 993 noted above, outperforms the Honda noted above (remember they want low blower speed and only the center vent open which causes even lower vent temperatures). This also outperforms my 3.2 Carrera with the RetroAir system that I was previously very impressed with. Don't forget, it also out performs what R134 "should" be capable of doing. Both of the local mechanics I work with here say this is by far the best A/C they have felt in a 911 pre-996 and are eager to start selling and installing the systems. This is in a car with no roof insulation all, black paint, not door insulation, and very thin RS carpet. I am very satisfied. That said, when it is 95+ and 40%+ humidity and the car is heat soaked it will take 15-20 min before I think of turning down the blower etc. That is simply function of the heat and humidity, not a fault of the system. I am comfortable quickly though. These old cars have nowhere near the heat insulation in the interior of a modern car like my X5, and those cars also have more room for a larger evaporator etc. Given the design requirements of our old 911’s this system is amazing.Installation Suggestions (random order) PRESURE TEST YOUR SYSTEM! Do not rely on vacuum testing it. Here in the USA most A/C shops look at you like you are an alien when you ask them to pressure test your system with nitrogen. No one here does that it seems, like they do in Europe. That said, the ONLY WAY to see if you have leaky fitting is to pressure test. Here in the US they want to vacuum test-system, and if it hold above 30in of vacuum for a period of time (overnight in my case) “you're fine.” Wrong! Vacuum sucks. Duh right? It sucks fittings TOGETHER. Pressure pushes, and it pushed 2 of my fittings apart to show a leak the I finally pressure tested like Jonny had been begging me to do. That little “mistake” meant I was chasing my tail for over a week, complaining to Jonny about how my system was not cutting it in Florida etc. etc…..OPS! 2 other people I have talked with did the same thing, and when I convinced them to pressure test…they found leaks. My system see’s over 170PSI at times in use. So pressure testing to that pressure should be sufficient.
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles Last edited by Duc Hunter; 06-03-2019 at 12:29 PM.. |
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Please install the footwell/crotch vents. I know the tubing may look like an afterthought but DO IT! I and a few others are working on some 3D printed vents that will replace the tubes Jonny & Co supply, provide the same function, and accommodate the cabin air return as well. Until then though USE the ones provided!! They make a massive difference in how you feel and how fast the car cools off. Don’t try smaller ones that look better, been there and done that too. I cannot stress enough to use them. I did not want to and have learned just how amazing they are.
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles Last edited by Duc Hunter; 06-03-2019 at 12:51 PM.. |
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My environmental Testing
I have spent over 60 hours testing on the roads in Florida. Temps have been as high as 42C (107.6F), as recorded on my VDO dash mounted outside air temp gauge. Humidity has been over 80% at its worst, and never really below 35%. Testing has been going on since late 2018. Additionally, tests have been run at night where temps are below 26C (78.8F), and in winter when temps were in the near 4.4C (40F). BMD=12.6
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles Last edited by Duc Hunter; 06-03-2019 at 01:36 PM.. |
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KI=.01 & KD=.01
These 2 settings are a little complicated to explain. Basically, they control how quickly the system backs off the compressor speed and amperage as the car approaches the CTS. One of them controls how hard it tries to back off as it approaches the CTS, and the other is how much it tries to predict/prevent an over shoot in CTS temp. PID controllers are used for all kinds of industrial uses, where they can over shoot easily, but on our case it won’t. Just change these to my settings and don't play with them. There is nothing really to be gained by moving away from my setting, that I can tell. Increasing them back to the 1.12 settings can slow your cars ability to reach CTS. In dry climates, or mild weather this might be desirable. I will have to re-test this when it cools off here (October maybe).System Comfort Setting Testing Your settings will need to be set specific to your desired cabin temp AND your install. Mostly, where and how your CTS sensor is mounted influences it's specific reading vs where you personally like the cabin to feel. This takes some testing, and specific testing in not super-hot temps (i.e. at night in the summer should be fine).Setting Goals Cool the cabin quicklyThings to Try, or Look For If you need to warm your car up during testing after its been cooling off, just roll down window and watch the vent temp rise, then close the window. Simple, but it took me a lot of testing to remember I could do this. You can easily get focused in the weeds of your numbers and system and forget simple things.
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles Last edited by Duc Hunter; 06-03-2019 at 01:33 PM.. |
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Testing Procedure
Part 1 CHI, CTG, etc……Put your system in high/low mode, not climate. This means your system will essentially run on high as long as it has enough amperage. If it does not have enough amperage for high (think at a stoplight) it will switch to your BLO setting. If it still cannot maintain voltage (which at BLOW=5 it should even on a stock alternator) it will switch off.
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles Last edited by Duc Hunter; 06-03-2019 at 01:25 PM.. |
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Part 2 - Home Stretch
Switch to Climate mode and change your CTS to the temp you decided was “cold enough” above. Go drive again at night and see if the setting you chose above works. Initially I chose 18C, and then I decided on 19C after testing in Climate mode. In fact, setting my cabin temp at 19C meant the compressor would slow to 5% (CLO setting), the vent temps were in the high 30’s/low 40’s F, and I did not want to turn the system off. The CLO being 5% is also key to be able to use this system to aid with defrosting in the winter, which you WILL do. Trust me. If you watch your evap temp you can see it rise as the system backs off to not over cool the car. At times I have seen mine come up from -4C to 6C to maintain cabin temps on a cool night.In Conclusion - Finally right? With the settings you have arrived at your car will run at max compressor speed/amperage, based on your alternator’s capacity, until it gets within ~1.75C (~2.8F) of your CTS (desired cabin temp). This is essentially as fast as you can cool the car given your equipment. Once the cabin temp sensor is within ~1.75C of the CTS the system will SLOWLY start backing off the compressor amperage and speed so as to not over shoot the CTS temp. It will also not feel “too cold” where you want to move the vents off your body as the temp reaches your cabin temp, except you will want to close off the crotch blowers before this point. As your cabin reaches “comfortable” the crotch vents become too much as they REALLY cool your body off. Your car will maintain good charging on the freeway, and can back off as needed at a stoplight, and should not have to resort to turning the compressor off/on (alternator dependent in some cases). There were many times where I got frustrated during my install process and vented to Jonny questioning the systems performance capabilities. Each time I learned a few things (some of which I have shared here). 90% of the time I had made a mistake though, or missed something, or had an air leak. Only once was it CR’s fault per se. I was one of the early customers who received some improperly machined fittings, a problem long since solved. That was literally the only issue that was not caused by my installation. On the other installs I have helped counseled, the same has been true. Installing an A/C System is not a simple thing. The CR kit makes it very doable, but there are a lot of moving parts. Their instructions are laid out pretty clearly. Between following them and reading this “little” guide I think everyone will find it a very satisfying project. Be methodical though, or as pilots say RTFM! Again, I am by no means an expert. I just wanted to pass along what I had learned. I will try to update this as I learn more, and hope everyone find it helpful. Thank you again to Jonny & Co for a great product, and great support. PS – Jonny, winter is coming (October/November for me) so get working on that heat! [/INDENT]
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles Last edited by Duc Hunter; 06-03-2019 at 01:42 PM.. |
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Hi Chris,
Great write-up! Please put me down for a pair of the 3D footwell vents when you start producing them. Regards, David
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__________________ David Yerkes 1987 911 Targa - GP White |
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Thank you very much for the detailed write up. I'm probably going to go this way with my build.
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Good job on your report and suggestions! I also have the CR A/C and like it a lot since most of its weight is up front (a condenser is in the driver side rear wheel well). I may be interested in a set of 3D printed footwell vents.
Have you ran your car during winter months with heat exchanger in exhaust headers? If yes then how was the heating? I don't have a heater box on my headers but I did tried using a flex tube along the headers but had no luck getting any heat due to ineffeciency of heat transfer and cold air coming in thru the A/C blower box.
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MikeD '87 930 |
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Great write up.
I appreciate the effort put forth. Very informative.
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Pete 79 911SC RoW "Tornadoes come out of frikkin nowhere. One minute everything is all sunshine and puppies the next thing you know you've got flying cows".- Stomachmonkey |
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Thanks for taking the time to post this for all of our benefit!
This seals the deal for me. I will, one day, be a customer of Classic Retrofit's AC system.
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87 Coupe - The Driver 78 Backdate - The Project http://forums.pelicanparts.com/porsche-911-technical-forum/979976-project-heavy-metal-all-steel-classic-remastered.html 85 Coupe - The Rot Rod! AX beater |
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This is fab. ty!
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles |
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Thanks for the info on the heat. I'm looking forward to see how well electric heat will perform and am curious where it will be mounted. I hope it's not inside the blower box (dread to remove the blower box with A/C already charged)!
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MikeD '87 930 |
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The rumor is, and my best guess is, that the heaters will go in the foot well area where the foot well blowers and later model cars went. This only makes sense as putting in there will add to the blower capability, and is a good place to put the heat, while keeping it out of the way of the air-conditioning system.
I also just want to reiterate to everyone to please check the chart above about r134. I talked to someone today who is complaining about not getting 40° vent a temperature of 100° day. Per the chart on a 100° day our 134 will be between 50 and 55 psi on the low side. As I understand it this means the evaporator is around 50 to 55°F. Therefore there is no way with R134 to get 40° and temperatures in 100° ambient outside air temperature.
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles |
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Wow. Nice write up. Kudos on a thorough job.
What do your printed footwell vents look like? Also, did you do anything with the lower center, “bow tie” vent? Thx,
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Frank Amoroso 1987 911 M491 / M470 Coupe 3.4 #PTSGeminiM491 1988 911 M491 / M470 Cabriolet #BlackM491Cab (sold) 1989 911 M491 / M470 Coupe #SpecialWishes1989M491 WTB / ISO: G50 911 M491 Coupe |
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Lower center “bow tie” vent? My car did not have one, nor did it have the hole for a bow tie vent. NOw I have though about plumbing something into the cabin to use the now capped 60mm output on the blowers drivers side. The best solution comfort wise would be to move the fuel gauge to where the clock is, and mount up a circular vent in to the hole the fuel gauge currently sits in. This makes for the easiest (and maybe only doable) routing of the feed hose, and could get a lot more air into the cabin and on the driver. That said I am not sure it is really needed yet. I am not sure it could be routed down to here the bow tie vent is front eh factory. IF it could, I would point it straight into the cabin unlike the bow tie vent. Remember this system as 2 x 60mm intakes, and mine is feeding 3X 60mm outputs, and 2 x 40mm outputs. The 3D printed footwell vents? Right now they are far too un-pretty to even post (and I made my first set wrong). Essentially they cover and mimic the bottom of the mixing valves exactly at their base. The hole closest to the passengers is left open, as this is the systems intake. The hole farthest from the passengers is covered and has a duct that comes up, and turns 90 degrees to blow at the passengers. This tube is 1/2” away from the hole closest to the passengers, to permit good intake flow, and extends well past the intake hole, to prevent the intake from sucking in the air you want on your body. It also only extends down from the underside of the dash a total of 3”, so it does not get in the way of your feet (I a 6’2” and have a size 12 shoe). This seems to flow enough air, and be up and out of the way enough. I am hoping to get some new prototypes built soon that work better than my first set. Using online CAD programs is a bit kludgy though.
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Chris - 1975 911s "Outlaw Rat-Rod" - steel wide body, 3.6 conversion 1989 911 Carrera 25th Anniversary Ed (5th from the last car to ever leave the original Porsche factory assembly line) - SW Chip, Fabspeed Headers & Exhaust, RetroAir A/C 2001 996 Turbo - ~42k miles |
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Frank Amoroso 1987 911 M491 / M470 Coupe 3.4 #PTSGeminiM491 1988 911 M491 / M470 Cabriolet #BlackM491Cab (sold) 1989 911 M491 / M470 Coupe #SpecialWishes1989M491 WTB / ISO: G50 911 M491 Coupe |
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Exceptional AC posting Chris.
Am curious, and forgive me if I missed it, what controls electric AC's compressor's cycling if there's no temp sensor inside evap?
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Karl ~~~ Current: '80 Silver Targa w /'85 3.2 Prior: '77 Copper 924. '73 Black 914. '74 White Carrera. '79 Silver/Black/Anthracite 930s. |
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