The stock AC system in perfect condition works great at night, or as a defogger in the rain, or on a sunny day below mid 80s outside. In full sun, at 95 or above, it just can't keep up. I finally gave up on the stock AC after driving to Fort Worth, TX in summer. On a HOT day, it just does not work well enough after hours in the sunshine, and especially if the car sits in the sun for a while and get heat soaked. The factory system will be useless.

For the residents of San Diego, Monterey, or Canada the stock AC is great. I live in Oklahoma. Right now it is 106 degrees and the heat index is 116. The stock system would be totally overwhelmed.

If you live in a hot area and want your wife to ride with you, or if you want real cold AC contact Griffith's. At the least, add in some condensers. I have four of them. This summer driving home on a 100+ degree day going due west in the afternoon the sun was shining on our chests, after driving for 7 hours. I tried to hold my hand on the dash, and it was too hot to do that. We (my wife was with me) were not cold, but we were not sweating.

I have driven my 911 to Key West in July, and was totally comfortable.

http://forums.pelicanparts.com/uploa...1658954890.jpg

Next year I will have a real test of my AC system. Palm Springs, CA in June. It will be HOT!

Cool you rebuilt your compressor! I ordered the parts kit and tried but it kept leaking. Was bummed. So I bought a rebuilt one on eBay. Works fine. But you are right , we can do lots of stuff but original AC will only get so cool. I had fun fixing it. Car is my hobby

81 sc,
R12A orig york update:
95F (35C) local today.
Filled last spring (2022) from dead empty, added ester oil to york , vacuum using oil extractor, end of story.
40 minute outing at 95F full sun, 20min, 5min idle, 20 min, 50 mph.
Two people in car, it's survivable, but I wouldn't want to sit in traffic with jeans and a shirt.
So feel good about your updated systems, I'm happy too, seeing as it's passable.
(At around 92F and 2 hours of highway driving, around 90mph, the a/c is barely manageable. I think too much air entry into cabin.)


Ha, that's my review of R12A for all yar Texaners, Arizoners.

I like my R134a ....blows easily under 40F on high fan.
Temp control full "cold" fan on high
http://forums.pelicanparts.com/uploa...1685648322.jpg
Temp control "warmest" fan on high
http://forums.pelicanparts.com/uploa...1685648389.jpg
But then I do have a big @ss parallel flow condenser with two puller fans up in the turbo tail...
http://forums.pelicanparts.com/uploa...1685648487.jpg
And other assorted goodies like a Sanden SD5H14 8" compressor and a Rennaire serpentine evaporator....

AC temp?
 

The Griffith evap and more powerful fan made a huge difference in my overall stock system. I get 33F temps on low fan while car is moving along. I have to turn the temp up often cuz it gets too cold in the black cabin. Yes I use envirosafe industrial. Yes it works unbelievably well, way way better than r12 or r134a. No I don’t want to hear your opinion about it lol.

My son was meditating or so it seemed on the way back from school in the 911 at 95F out, I was happy he was minimizing his thermal output! I checked the temps in Arizona this week, wow, 102F, that's crazy. I would modify a/c living there. (I've read r12a has more cooling capacity than r12 and r134a, but still won't handle the south I'd bet)

tsuter, I like your fans! That's serious gear.

Phil

Fans are cycled with a trinary switch so mainly they will come on at stop and go when there is less air down through the tail condenser.

The condenser is 16" x 30" from ACKITS and the fans are Permacool Turboflex 10" x 2" rated at 900CFM each

Here are the stats:

Ambient temp measured above condenser - 103F
Vent Temp - High Chill - 32F
Vent Temp - Low Chill - 58F
High Side Pressure - 190-240psi with condenser fans cycling on trinary switch
Low Side Pressure - 19-22psi
Engine Temp - Normal - Needle just below horizontal after 30 mile run 92F ambient air temp
Refrigerant - R134a 18 oz

Empty original York system with original dryer, vacuumed with oil extractor over night and filled with 12a spring 2022. Wasn't even sure it was going to work at first.

20 minutes, 5 minutes idle, 20 minutes. Roughly 50 Mph, total 45 minutes.
2 adults in car.
Fan and A/C set to max.
Meat probe stuck into vent, not touching walls. (add some vinyl tubing to top of probe section so it's just fat enough to friction fit in middle vents)

90F/32C Sunny
Humidity 43%
Roughly 50 Mph, 4th gear between 2k - 3k rpm: 55F/13C.
Idling for 5 min in sunshine: 64F/18C.

Checked today.

tsuter, yours in high chill is impressive.

Phil

http://forums.pelicanparts.com/uploa...1685735821.jpg
After a recent compressor change due to a leaking front nose seal, I went for a drive on a 88 degree full sun day. The return line from the evaporator to the compressor was frosted. It keeps the compressor cool, just like the driver.

http://forums.pelicanparts.com/uploa...1685735821.jpg

This is the inside temp from the little bitty vent. The air blowing out of the center vents is too much to keep the thermometer in place and it just blows out.

I was freezing so I had to turn the temp up. I am hoping for a good hot high 90s day before I go out to Palm Spring in a few weeks to give it a real test.

I sold my soul to the A/C devil . . .

http://forums.pelicanparts.com/uploa...1685772553.jpg

http://forums.pelicanparts.com/uploa...1685772758.jpg


In all honesty once the system warms up the vent temp also creeps up (40 degree range)

^ That's because you have frozen your evaporator and it is blocked with ice. The air then finds 'another route' through the evaporator but the area for heat exchange is reduced so the temp goes up. Eventually the whole thing is blocked and there is no air flow and no cooling.

Anything below freezing (0C / 32F) is unsustainable. Looks impressive as a snapshot but ultimately doomed to failure. Usually you want a few degrees above freezing to have an effective and 'long lasting' AC experience.

...Which indicates your refrigerant charge is incorrect, or sensors aren't working right.

http://forums.pelicanparts.com/uploa...1685969424.jpg

It’s possible to drive an evap below freezing without it “blocking.” Is necessary to know how much ice is doable. Endoscope mounted in plenum enables a live view to what’s going on icewise. Trick then is to cycle the compressor so there’s enough but not too much ice---air passage through evap is always preserved. When the compressor cuts OFF, cabin air quickly melts what ice exists. Compressor cut OFF here is set at 29 dF (as measured inside the evap) and cut ON at 32. Temps inside the evap have momentum—as “RN” noted—so temps in evap dive lower than 29 and float higher than 32. This cycle of freeze & thaw is functional given the humidity this system usually deals with, 60 - 80%. (In drier climate, evap would not be dealing with as much moisture and so could run to a lower temp.) Evap does not have equal temps throughout---there are colder places than others (so where a sensor is placed matters. Placing it in a warmer location results in the compressor running longer and so providing more cooling to the cabin.)

This: 3 condensers. Griffith Serpentine evap. Engine bay is sealed to get the engine’s cooling fan suction pulling air majorly through the rear lid condenser. An Arduino with a number of sensors has replaced the factory thermostat. Charge = 23 weighed ozs R134 done after a 12 hour evacuation that includes the charge hose—so zero air/moisture introduction when going from evacuation to charge. Charge is liquid, not gas. Temp & humidity info is displayed in real time by a small screen mounted in the center console. Analog pig sticker (in center vent) does not keep up with the real time digital “Evap” sensor readings.

Nick... it "could" be lower but not necessarily "should" be. Vent temps are always subject to the state the whole of an AC system is in---doesn't matter what year your 911 is. If everything but one thing is in good order, that one thing drags the whole of the system down---sending vent temps in the opposite direction. If you're interested, I suggest checking the intake side of your evap for debris build up. Then checking the intake side of your condensers. Condensers not only get debris on them but they crud up. That crud is insulating. That insulation curtails an efficient transfer of refrigerant (cabin) heat to the outside ambient air. A good cleaning of that aluminum (or copper if you have) is a step in the right direction. Sealing your engine bay is a fine way to use the engine's fan to increase the air flow through the rear lid condenser. That alone can get you a few degrees provided other areas are in order. (Engine fans move a shi* load of air!) It's incremental system improvements that add up to lower vent temps.

Good to hear you're feeling better!
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TBH, although ice looks 'impressive' it is never a good idea. It's insulating and reducing the surface area of the the heat exchanger thus preventing it from working at maximum efficiency. Ice indicates the beginning of a downward spiral of performance.

In my experience, you'll never recover from an ice up without shutting off the system for some time. It's impossible with one evap temp sensor to guarantee that all parts are ice free if the cut off temp is too low. Better to run a few degrees above freezing.

In these cars the evaporator freezes for two common reasons:

1. Lack of air flow across the evaporator. Get a better fan and put it on high. If it freezes on low speed at high ambients like 95F plus and not on high speed that is actually pretty dope!

2. Refrigerant is too low. When the pressure is too low in the coil, moisture freezes on the coil. You can guess this if it is freezing up AND the fan speed is on high.
Hook up your gauges and check your pressures.

Other reasons are much much less common. Like dirty filter restricting air.

For anyone wanting to genuinely understand AC operation, the above is nonsense. More to the point, it’s blatantly misleading and worse, it’s coming from someone who knows (should know) AC.

In reality…

Ice doesn’t prevent a system from “working at maximum efficiency.” Rather, it proves a system is working at max efficiency. Being an “insulator” and “reducing surface area” when a system is already performing… is like saying “that plane cannot fly” after it’s in the air. The supposed “downward spiral of performance” …thermostatic control is what cycles the compressor on & off to prevent this, so in fact there is no downward “spiral.” To guarantee an evap is thawing completely, one must know the humidity and hystersis an evap is operating under. Then actually see the evap cycling to confirm what’s happening. I happen to know my system’s cycle of ice-thaw-ice-thaw etc from watching the evap operate in real time. The ice-thaw cycle is perpetual with the transition between icing and thawing occurring rather quickly & completely. The efficiency of this cycling including hysteresis was deliberately taken into consideration when defining & testing the program that runs this AC. Control here is digital, driven by an Arduino with 2 sensors inside the evap, 2 in the cabin, and 2 external.

I’m not in a pizzzing match with Jonny. My input here is to set the record straight. Jonny is one among others who sells AC systems. Charlie Griffith is another. I started with Griffith’s “Ice Man Project.” Ice is a good thing when managed correctly.
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