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  • #16
    In answer to the query about vent temperatures, which may not have been directed to me:

    They vary depending on many factors. Ambient temperatures here in the summer typically run in the 80s or 90s, and when i'm using the AC in such conditions the vent temperatures typically run between 40 and 50 degrees F. I can get temperatures lower than that, but then it gets too cold inside the car. When ambient temperatures get up to 110 degrees or so F, vent temperatures may run between 50 and 55 degrees F. The temperatures rise a little bit when the car is not moving.

    But it's a mistake to focus too much on vent temperatures. What you want to know is how much heat the system is capable of removing from the air, and that depends on a lot more than just the vent temperatures. A major factor is how much air is moving at those temperatures, and there's no easy way to determine that. I disagree with one of Frank Beck's statements about the factory Behr system: "Inefficient evaporator and too far away from the dash vents." In my experience, that's simply not the case. I did replace the evaporator with a more efficient one, using the original evaporator housing, but I have no reason to doubt that the original one would have been capable of reasonable performance. Ialso question his statement: "Evap fan is inefficient causing low volume." I also replaced the evaporator fan motor with one that moved a little more air, but the difference in airflow is not that great.

    The AC is a system intended to produce a subjective result, comfort. So as long as it does that, I think that there's no reason to fixate on vent temperatures (although, because i'm an engineer, I have a hard-to-break habit of p[aying attention to such things).

    So I'll provide you with some subjeective information. When the car sits outside in the sun and the ambient temperature is above 100 degrees F, the interior of the car gets pretty hot pretty fast (I rarely do this, but it has happened on occasion). Running at maximum capacity, the AC can make the interior of the car tolerable in no more that about 5 minutes, and get it down to a temperature that we would choose in about another 5 minutes. It works better than the AC in my 993. My wife thinks it works better than the AC in her Boxster. I think that's a bit of an exaggeration, but if she's happy, I'm happy.

    As to the comment about two many components increasing the chance of leaks, the system was last charged about 2.5 years ago. I suspect that it has lost some refrigerant over that period of time, but just last week we had temperatures well above 100 degrees and the system worked quite well, so whatever loss of frean that might have occurred must have been relatively small, not enough to affect performance significantly. I'm not sure that the additional components are more of a factor than the fact that the system has about 40 feet of barrier hose, but that appears to be working well.

    Someone commented on getting rid of the condenser under the rear deck lid grill. I thought about that at the time I was deciding how to configure the system, but ultimately decided not to do that, in par on the basis of Grif's recommendation. The compressor feeds freon to the condensers in the following order: rear deck lid, condenser behind the left rear wheel, condenser in front of the left rear wheel, condenser under the nose. And then, of course, to the receiver dryer and the evaporator. Feeding the rear wheel well condensers first, then the rear deck lid condenser, might mitigate, under some circumstances, the extra heat added to the air coming in through the grill, but it wouldn't do that when it counts the most, when ambient temperatures are highest, and it would require even a little more hose. In any event, with the external oil cooler, which is a good idea anyway, it's not a problem.

    It may be that someone can make a system with only two condensers that works as well as this, but I'm skeptical. In any event, I've been pleased with the way this has worked out and would recommend the Griffiths system. It's well thought out, the components are of high quality and the support from Griffiths is excellent. It also makes good use of various components of the old Behr system and requires no modifications to the car.

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    • #17
      Originally posted by pilotdave911 View Post
      I disagree with one of Frank Beck's statements about the factory Behr system: "Inefficient evaporator and too far away from the dash vents." In my experience, that's simply not the case. I did replace the evaporator with a more efficient one, using the original evaporator housing, but I have no reason to doubt that the original one would have been capable of reasonable performance. Ialso question his statement: "Evap fan is inefficient causing low volume."
      With all due respect, I would like to think Frank knows what he's talking about here.... Having years of firsthand "real world" experience is an invaluable source of knowledge. I'd also like to think someone who lives in AZ prioritizes a functional AC system Furthermore, if the stock system works as well as you "believe" it does, how come virtually no one retains its use? Why do those that purchased these cars new with factory AC even admit that it never really worked that well?

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      • #18
        Porsche didn't figure out a/c until the 964, and then those always had leaky evaporators. My 930 was probably the worst, tiny condenser over the engine, the front condensers fan was pitiful and the dash vents were awful.
        The 964 had the condenser in the front left fender, where it got decent airflow. If you have good airflow a smaller condenser works, I don't think the rear wheel wells have good flow, but I guess having more area makes up a bit for that.
        Vent temps, as stated above have too many variables. Higher fan speeds, higher vent temps. On a 100 degree day if I am getting 50-55 degrees at the vent, I am happy and comfortable. That is a 45-50 degree drop from outside air temp. Pretty damn good for any a/c except maybe for a Chevy Pickup.

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        • #19
          Originally posted by flatsixer View Post
          Porsche didn't figure out a/c until the 964, and then those always had leaky evaporators. My 930 was probably the worst, tiny condenser over the engine, the front condensers fan was pitiful and the dash vents were awful.
          The 964 had the condenser in the front left fender, where it got decent airflow. If you have good airflow a smaller condenser works, I don't think the rear wheel wells have good flow, but I guess having more area makes up a bit for that.
          Vent temps, as stated above have too many variables. Higher fan speeds, higher vent temps. On a 100 degree day if I am getting 50-55 degrees at the vent, I am happy and comfortable. That is a 45-50 degree drop from outside air temp. Pretty damn good for any a/c except maybe for a Chevy Pickup.
          My Tacoma's will freeze you out. Fortunate to have that here in FL.

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          • #20
            Each of the condensers in the rear wheel well has its own fan. These fans cycle on and off with the compressor clutch. These fans together draw about 9 A, which obviously contributes to the electrical load and is probably the major reason that the Griffiths system draws more than the factory system, although the upgraded evaporator motor draws a little more also.

            As I said above, vent temperatures go up a little bit, about 5 degrees, when the car is stopped and I am sure that is due to decreased airflow over condensers. I'm not sure exaclty which ones, however, At idle, less air is flowing through the condenser under the rear deck lid, and I think that the condenser under the nose must see greater airflow when the car is moving. Perhaps forward motion contributes to heat loss from the rear wheel well condensers as well.

            i agree that vent temperatures of 50-55 degrees F are adequate to keep the car comfortable as long as the volume of air is good.

            As far as I know, the AC units in the 993 and 964 were similar, right down to the tendency of the evaporators to leak. I never looked to see where the condenser was in my 993. I had it for 22 years, until one day when my wife was driving it home from her office and, while stopped at a light, rear ended by a big SUV. The car was destroyed, although it managed to protect her reasonably well. The AC in it was, in my opinion, mostly adequate, although it struggled at ambients above 100 degrees or so.

            I have heard people say that 30 degree differential between vent temperature and ambient temperature is about all you can expect from a car air conditioner, but in my experience most are better than that. The Griffiths system will manage a 55 -60 degree F difference at an ambient temperature of 110 degrees F.
            pilotdave911
            2.0L
            Last edited by pilotdave911; 09-25-2022, 02:35 PM.

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            • #21
              More than way to achieve an end, however I prefer simplicity. Just for comparison the 964 A/C worked really well with one condenser + fan in the front left fender.
              If I didn't have the 2 battery setup, that is what I would prefer.
              Click image for larger version  Name:	911-PT-AC-install.jpg Views:	0 Size:	96.0 KB ID:	7824

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              • #22
                Very good.. Perhaps the 964 AC worked better than the 993 AC. For whatever reason, you seem to have had a better experience in your 964 than I had in my 993. I thought that the 993 AC. although not bad, was just mediocre. I'd not use the term "worked really well" to describe the 993 AC.

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                • #23
                  Were you on R12, or R134a?
                  So many factors can vary. I thought the 964 had great airflow and cooled very well, in comparison to most early 911s'
                  The best auto air conditioner i've ever experienced was the trunk mounted friga king in a 1959 Silver Cloud.
                  I think they sourced it from a commercial meat transport. It would literally create frost inside the car no matter the outside temp. Two tube outlets from the rear shelf with huge output, twin fans . The Dallas importer installed these units, as the british factory unit was wimpy.

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                  • #24
                    I believe that the 964 ac used R-12, and the 993 used R-134a. A significant problem with those systems was the tendency of the evaporators to leak.

                    The evaporators in earlier cars were relatively easy to change and did not, as a rule, fail. However, the one in my 993 did, and it seemed as though the evaporator was the first thing to come down the belt on the assembly line, with the rest of the car being built around it. Changing it required a major effort.

                    Perhaps the difference in refrigerant is why you liked your 964 AC better than I liked the 993 AC. However, I'd agree that the system in the 993 was better than in the early 911s.

                    Frank Beck made the point that the evaporator is too far from the dash vents. While it's true that having the evaporator within the knee pad would be bettter, there's not much room there and it would require a unit specifically designed for that purpose. My experience with the system I put into my car indicates that is not a major problem. Also, I replaced the original evaporator with a new one from Griffiths, along with the two existing condensers. I don't know how much more effective the new evaporator is than the old one, but the construction is different, with greater surface area exposed to the freon. The system is sufficiently effective that once the car is cooled down, running the system at about half capacity is adequate to maintain cool temperatures in the car at any ambient temperature that I've experienced.

                    With my "84 Supra, i always ran the AC at maximum whenever I was using it. I had about a 15 minute drive to my office and by the time I got there I could see my breath in the car.

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                    • #25
                      Originally posted by pilotdave911 View Post
                      I have a 1973.5 911T coupe that i use as my primary vehicle in the Los Angeles area. I bought it almost 20 years ago with that in mind but only relatively recently (a few yuears ago) did the work it needed to be useful in the summer. It had a Behr 2-condenser setup which was not functional, but all parts were present.

                      First I installed the front oil cooler kit from Elephant Racing because I did not want to see excessive oil temperatures while using the air conditioner. The support bracket for the oil cooler was made for later 911s and so has to be reworked a bit but otherwise the installation was straightforward. I can provide some tips on this if anyone is interested.

                      Once I was satisfied that was working well I proceeded with the air conditioning upgrade with the 4-condenser setup from Griffiths. The kit is made for a range of cars up through 1989 and i found that one or two things didn't fit quite as advertised, but only minor changes were required. This uses R-134a refrigerant.

                      Although I haven't been able to reproduce some of the numbers that Grif posts on his website, I think that from a practical standpoint the unit does what he says it will, which is to keep the car comfortable in ambient temperatures up to and exceeding 110 degrees F. In those conditions, the oil temperature runs in the range of 205-215 degrees F, at the upper range of normal. I have found that when using the air conditioning, the oil tempearature runs in the range i gave, almost independent of outside air temperature. I think that this is because, at least in part, as the temperature increases less heat comes out of the rear deck lid condenser and the other condensers become more important. The only thing I would do differently if I were to do it again would be to get the continously variable evaporator fan control, but it's not a big deal. The original Behr knee pad is perfectly adequate. I have found that factory support from Griffiths is excellent.

                      The only quibble I have is with Grif's claim ihat the stock alternator is adequate. I was skeptical of that and probably would not have proceeded if a high output alternator was not available (95A from Pelican Parts, no longer offered). Depending on evaporator fan and temperature settings, the ac system draws up to 33 A. The stock 50A alternator in the early cars will only generate about 10 A at engine idle speeds, so discharge rate from the battery when stopped at a light can get to be quite high, and the stock alternator lacks sufficient reserve capacity to recharge the battery during the short distance to the next stop. A high capacity alternator is available now from an outfit with a website classicretrofit.com. I have no experience with their product but it looks like it would be at least as good as the alternator I got from Pelican Parts.

                      Solving this electrical problem turned out to be more difficult than just replacing the alternator, although that is a necessary part of the solution. However, I managed to do so and no longer get home and find that the battery lacks enough charge to restart the car to drive it into the garage. If anyone is interested I can discuss this problem and the approach to solving it in detail.

                      What did you have to do to get the high output alternator to work in your car?
                      Former British Leyland mechanic, remember them?
                      Long Beach, CA

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                      • #26
                        British Leyland, huh? That brings back memories. Lucas electrical stuff too, i suppose.

                        To make a long story short, the existing electrical system has two relevant problems. One is that, because the batteries (two small ones in parallel were used in 1969-1973 911s) are located up front and the engine and alternator are in the rear, long cables, analogous to the long hoses in the AC system, are present. Also, the alternator is located in the cooling fan hub. I suppose that the design of the fan dictates the speed, but, for whatever reason, the alternator to engine speed ratio is only 1.3:1. Alternator experts have told me that they assume that alternators have a ratio of 3:1 and that the ususal test equipment can’t simulate anything below about 2:1. I understand that somewhat later 911s upped the ratio to 1.8:1 and in the final iteration of the air-cooled 911 the alternator ran independently of the cooling fan. I also found that the wire from the alternator output down to the starter motor, where it connects with the large cable running up front to the batteries, was quite small, inadequate for the current I needed it to carry. I came to these conclusions after making detailed measurements on the relevant portions of the system under load, so that I could see exactly where voltage drops were occurring.

                        The first step was to run a 6 AWG wire from the alternator output down to the starter, which I ran in parallel with the existing wire. I also added a second ground strap to the alternator, cleaned all other grounds and made sure that all other connections in the system were performing properly.

                        While I was working this out I sent the high output alternator to a shop to find out exactly what it was capable of. The data they sent me show the following current outputs at various rotor speeds:
                        2000 rpm, 76 A corresponding to engine speed of 1540 rpm;
                        2500 rpm, 92 A, at engine speed 1920 rpm;
                        3900 rpm, 117 A at engine speed 3000 rpm;
                        8300 rpm, 166 A at engine speed of 6400 rpm (just above red line of 6300 rpm).
                        They were not able to take measurements at any lower rotor speeds.

                        I needed to know what was going on in real time, so I built some electronics to display net charging current into the battery on the voltmeter I had previously installed. With this system, 12 V corresponds to charging of zero A, and ;each volt above or below 12 V means an additional charge or discharge rate of 5 A or 20 A. I used Hall effect sensors around the cable running between the batteries and the starter and around the cabling feeding the various loads off the batteries. A switch under the meter panel allows me to display battery voltage or either the high or low sensitivity display of charging current.

                        From this I learned that the high output alternator generates nothing up to about 1000 rpm engine speed. By about 1100 rpm, it’s able to supply the basic needs fo the car (about 10 A., mainly for fuel pump and ignition) and by 1400 rpm it can fully support the car, the air conditioner and all lights. By comparison, the stock alternator is capable of 10 A at engine idle (abut 800 rpm) but as I mentioned in my initial post, lacks the excess capacity to charge the battery in between periods of idling when the AC is running. At idle with the AC running, the discharge rate can get up to 45 A, which explains the problems I was having.

                        The real solution would be a simple planetary gearbox to increase the alternator speed by about 35 or 40% over the fan speed; it would have to be a sealed system and take up minimal space, and that is beyond the scope of what I can do. But it’s a simple matter, if I’m at a light and the AC is on, to reach over with the heel of my right foot and goose the gas peddle a little, until the discharge rate goes to zero. Despite what the alternator is capable of, I have not seen charge rates of above about 25 A, which correspond to a total alternator output of 70 A or so. I am pleased that because every 62 A of charging corresponds to 1 HP into the alternator (actually about 1.25 HP, allowing for losses in the alternator and the field current which isn’t seen in the alternator output), and the extra belt tension required to generate higher levels increases the strain on the fan housing. Considering that the original alternator load maxed out at about 1 HP, I’d like not to exceed this by very much. I’m not sure what would happen if I tried to rely on the alternator to restore signficantly discharged batteries.

                        So this has solved my problem, and since putting this metering system in a few years back I have not had further occurrences of getting somewhare and finding that my batteries were not fully charged. I hope this answers your question.
                        pilotdave911
                        2.0L
                        Last edited by pilotdave911; 10-01-2022, 05:29 PM.

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                        • #27
                          Thank you for that thorough explanation, Dave.

                          Yes, I worked in a dealership and attended British Leyland training in Leonia, NJ in the mid-70s, when the British car industry was reaching a low point. The company had good people, but the quality from the factories was dismal. This was when the TR7 was a year or so into production. The Triumph motor was a clever design, but it wouldn't work until Saab made their own version. Too bad, the British car legacy was a fine one. I liked pre-Leyland MGBs a lot.
                          Former British Leyland mechanic, remember them?
                          Long Beach, CA

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                          • #28
                            Originally posted by Tom F2 View Post

                            Yes, I worked in a dealership and attended British Leyland training in Leonia, NJ in the mid-70s, when the British car industry was reaching a low point. The company had good people, but the quality from the factories was dismal. This was when the TR7 was a year or so into production. The Triumph motor was a clever design, but it wouldn't work until Saab made their own version. Too bad, the British car legacy was a fine one. I liked pre-Leyland MGBs a lot.
                            In the '70s and late '60s i was working as an engineer at JPL. The hot Triump at the time was the TR6. I knew a number of people at the lab and elsewhere who had them and if i had wanted an MG or Triumph instead of a Porsche I think that's what I would have gotten. I don't recall ever knowing anyone who had a TR7 or TR8. The main competitor to the 911 was the E-jag, and they were well-represented at the lab. I knew people who had them. The usual experience seemed to be that you had to make your E-jag into a hobby if you wanted to keep it running. The 911, by comparison, was practically bullet-proof. My car still has a lot of the original components in it, such as the CD ignition. What I have found is that if one of those original parts fails, after 40 or 50 years, then the replacement is likely to be not nearly as good, and so whenever possible it's preferable to find someone who can rebuild the original part rather than buy a replacement from Porsche. I have recently been through this wilh the fuel pump. The original finally started to leak after about 45 years. Outrageously-priced new replacements each lasted a little longer than two years (just past the warranty period) and i was able to find someone who could rebuild it for a fraction of the cost. So far it's working well. I'm still trying to find a good replacement for the fuel level sender.

                            Other friends of mine had MGs; the one preferred by my friends that got them was the MGB GT. Of course, in the early '70s the 240Z came along and gave all of its competition a run for the money.

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