Let me get this straight, an AC system is suppose to cool right? Griffths system does exactly that. Why would his or anybody else's system address MRT factor? The owner of the vehicle has the option to tint in the hopes of keeping the temp down during stationary times. We all should know that tints help with temp. A front reflective sun shade might work as well....but that has nothing to do with the AC..and why it may or may not work.

In a modern car, an AC may have an auto function. It continuously monitors the temp in the cabin and adjust. THESE ARE NOT MODERN CARS OR MODERN AC SYSTEMS. STOP TRYING TO COMPARE SYSTEMS. Your adding variables that have nothing to do with cooling in these old girls...keep it simple...

Did you know that Pelican actually suggests adding a cooling fan to the rear lid condenser?

^^^ wwest, your assumptions about general human comfort standards, and the idea that cool/cold air blowing on one's person (in hot/humid weather - aka: when a/c is most used) increases discomfort levels, are way off base. How can you assume to speak to the comfort needs of all human beings living in every imaginable climate? Get real, man - aren't you feeling the pinch of embarrassment over the absurdity of your remarks?

Saying that Griff's system is not capably of cooling a 911 interior to a measly 75 degrees, even with ambient temps above 90, is denigration - plain and simple.

No, he doesn't. He knows better than everyone what folks need and want. And he has a "solution" to make sure you get what he, errr, you want.

Embarrassed, no, not even for the ignorant. Lots of reading to do...


http://www.energy.wsu.edu/Documents/10_spr_iaq_nl.pdf

Manipulate the chart yourself...

Try setting the air temperature to 0 Centigrade and the air movement/flow anywhere on the chart...

http://wiki.naturalfrequency.com/wiki/Human_Comfort

Page 11...

http://www.labeee.ufsc.br/antigo/arquivos/publicacoes/Thermal_Booklet.pdf

There we go again, ambient temps are not the singular issue in the human comfort equation.

Home, window air conditioner. Enough cooling BTUs for the entire room or not enough so you must set closely in the dry/cool (""icebox" cold?) "discomforting" outflow in order to be "comfortable".

Which would YOU choose?

Be that as it may, has anyone, ANYONE, done enough of a survey of the average cabin temperature of an air-cooled pre-1989 911 with A/C in 90F climate?

Inclusive of MRT?

Again, I'm not saying Griffiths is at fault, their system will supply a more than plentiful level of cooling airflow, even COLD, discomforting airflow if you are attempting to bring the cabin, on the average, down to 75F in a HOT climate and BRIGHT sunlight.

Overcoming that problem requires addressing something more than just surrounding air temperature. Beginning with window tint, even windshield film now that a clear one is available. Haven't I seen pictures of owners applying products like DynaMat to help keep the radiant effects surpressed?

You will never reach the level of a typical Lexus LS, but some progress can be had at relatively low cost.

West, rather than rely on your own narrow ideas about "comfort", and on what you can mine out of books and papers on the subject, why don't you ask 911 owners with modified a/c systems if they are "discomforted" by the cold air blowing out of the vents?

As I have stated, I have frigid vent temps which make the whole intererior feel cold, even on hot and humid days. I love it, and so does anyone that rides along with me - they are amazed at the air quality in my car and comment that it is superior to many modern vehicles they are familiar with.

Believe it or not, to anyone motivated to modify their 911 a/c systems, very cold air blowing out of the vents is good, and if it is cold enough in the car that the thermostat can be turned to less than max, then we're talking ultimate success.

BTW, why does the comfort level that other 911 owners experience matter to you? You do not have a highly modified 911 a/c system blowing cold air in your face, and are thus not suffering what you call "discomfort" from such, so what has sparked your interest and concern?

While not "highly" modified(***1), I find myself wishing, searching for a way to reduce the discomfort level caused by cool and dry airflow to my, and my wife's, face and upper body. Thinking of using a SPAL(:rolleyes:) fan instead of the blower wheel for A/C evaporator airflow..reverse the airflow(***2) direction once I switch from COLD system outflow for initial cabin cooldown. Cool/dry high velocity(911 requirement) airflow is not as discomforting from the footwell.

***1 My A/C modifications have centered on increasing the system's refrigerant condensing capacity in low speed stop and go traffic, the MAJOR shortcoming of the factory system.

***2 Double WIN! Downward airflow direction would help to force condensate down and out the provided drain, instead of right back into our face. Maybe triple win, no debris "sucked" onto the evaporator WET side and maybe "glued" in place there.

I quoted you again to note that this really is the only reasonable course of action - wwest's most recent post in this thread, where he offered line-item nonsense, and even falsehoods, to a post of mine, really emphasizes how useless interacting with this guy really is.

And to Eric, yep, I must be one slow learning MF!!! :)

Accusing someone, anyone, of offering nonsense, telling falsehoods is a empty, groundless, accusation absent a statement making your case.

Forthcoming foundation for the accusation or just more Cluck, cluck, cluck.....

I have cracked corn ready....

Yeah, it's always great when you tell him something and he says "I don't believe you!" (Or something similar).

LOL, like the world revolves around feeding Wild West some of his own medicine.

LMAO.

Thanks everyone for their help. I got it charged and blowing cool air but the front condenser blower stopped working. Troubleshooting results:

1) The blower will run with 12vdc directly connected.
2) The fuse and relay have main power and I even tried swapping the fog light relay in.

System will not turn on the blower and the wiring diagram from Bentley has me a little confused. What are the DME Control Module, AC Temp Switch and Electro-magnetic coupling? How do I test them?
http://forums.pelicanparts.com/uploa...1409347168.jpg

Thanks,

P

Hi,
Please try jumpering 30 to 87 on the condenser relay. That confirms wiring OK.
Then jumper 85 to 86 that confirms relay OK. BTW sometimes the male pins on the relay lose contact with the socket. You can spread the pins open a little with a razor blade.
Let's see what that shows.
Good luck,
Dave

Weird. Jumpering the relay socket #30-#87 with the AC running did not cause the blower to run and #30/ #85 measured 13/ 11.3V, respectively. Seems I may have a break in the connection between the relay and the blower.

Thanks Dave.

Make sure you have 12 volts at #30 of the relay socket. If not the problem is further up the line.
Dave

Hah. It turns out that the body shop plugged the wrong connector together at the blower. Once I found the other one after tracing from the relay, I plugged it in, tested and everything is working. Of course, I am still only getting vents about 25F below ambient. I will survive for our last couple of hot months. Thanks everyone.

:P

I am glad you found that wiring problem. Does your 25 degree difference reflect how cold it gets with the doors and windows closed and the system recirculating and cooling for a while?
Dave

Sadly, yes. Over about 15min of driving it went from 83F to 58F. I probably need to check the pressures again now that I have the additional "condensing capacity".

P

Sorry, P. Please post your P's and T's and maybe we can spot something.
Dave

P,
Looking back over your posts, your system is very similar to mine. Mine required 23 oz. of r134. My vent temps are sub 30 to mid 30's. I remember you charged with 48 oz +/-. Your problem could be as simple as modest overcharge of system. P/T should help spot this.
Dave

I originally put in 3-4 cans but later evacuated, pulled vacuum and currently have approx 20oz in. Less than two cans before I hit target pressure. I need to recheck pressures tomorrow.

OK, some lessons I have learned on my Summer vacation...

1) Before charging, pull a vacuum for a few hours to get the moisture out. My lesson here was that the first time, I was having issues with the schaders on the test ports. You can tell by watching the gauge. If it nearly instantly goes to 30Hg Vac, you have a valve lineup issue. It should drop to >20Hg fairly quickly but then take a few minutes to get to 30. I figured this out pretty quickly.

2) After pulling the vacuum, close the valve on the gauge set, turn off the pump, and let it site for at least an hour. It should stay at 30 or you have a leak. I actually got this part right too.

3) When charging, the car should be running, windows/ doors closed, AC on max, AC clutch engaged (center part turning), front condenser fan running, evaporator fan running and.... car at >2000rpm. This is important as it more accurately represents driving conditions. I got half of this wrong the first couple times.

I saw significant pressure differences without the front blower running, with the car at idle vs 2-3k rpm and, as mentioned previously, the consensus is doors/ windows closed. I most recently had nearly everything right except the front blower and maintaining >2000rpm. I stopped adding R134 when my pressures hit 40/270 but the car was only getting ~25F cooler than ambient. OK but better is achievable.

I fixed the front blower, used a piece of wood to keep the rpms up and my current pressures are 12/190 at 85F ambient. I will add some more freon, recheck and then let you all know.

Of course, if anyone believes I have made another error or misstated a lesson, please provide the correction.

Sounds promising. How much R134?
Dave

Pato, your checklist looks good/thorough, but I want to mention that the 2K RPM deal is not necessary - charging at idle speed works perfectly and renders excellent results. Experienced techs that I know personally charge at idle speed, and I have been doing so for many years as well. That said, there is no harm in charging at 2RPM, but it is not needed.

Thanks Ronnie, I tend to agree as I am not seeing the change in pressure I saw before. Low side tends to drop with increasing rpm but high side doesn't really change. I probably imagined it.

This system has me frustrated. It is blowing cool air but not cold (low 60's). This morning, I checked the pressure and it was 12/190. I just checked again just now and it was showing 10/230 (after running for a while). I added some freon but stopped at 20/ 260. I am worried as that pressure ratio is too high. Weird as it was 40/270 back when the front blower wasn't running. Ambient is 90F.

Do you think the gauge set or my test ports may be affecting my readings? Maybe my TXV? Blockage?

Sorry P,
It sounds like you have inadequate condenser function. All a/c systems are eventually limited by their heat exchangers, mostly condenser capacity. Could be air movement, refrigerant flow, or something else. If I recall, you have an ackits parallel flow condenser. When new, they should work great. If you suspect any debris in system, these condensers act as filters, due to small passage size and need replacement. They are not really flushable. May not apply to yours. Sorry.
Good luck,
Dave

With R134a in your 911 or 930, at 90F ambient:
at IDLE,
DECK LID RESTING ON SERVICE HOSES,
WINDOWS CLOSED,
FRONT CONDENSER BLOWER RUNNING,
THERMOSTAT MAX COLD,
ANY FAN SPEED, TRY speed 2,
HEATER BOXES ARE CLOSED (you crawled under the car and checked),
FRESH AIR VENTS CLOSED (top controls in dash to the left),
NO air infiltration coming through dash (for example, the trunk carpets are covering the back side of the dash).

In a perfect world you want something near 238 psi on the high at 90F


Low side pressures can vary for many reasons:
A) first is evap temp, a low pressure can signal a cold evap,
or an evaporator with low pressure drop(design of the evap)
B) clutch engaged or not engaged
C) TEV opening and closing.... and don't blame the TEV, that's the first mistake
novices make; including "Qualified/Certified MBA, Gold Certificate, MasterMechanic, SAE blah blah technicians ... Porsche "experts".

The avg for a normally running stock system can vary from 20-40 and it all depends upon what else is happening.


When you are charging a system there are 2 things you are looking at:
1) The amount of refrigerant, and
2) The P&T; what is the ambient outside air temperature and what is the high side pressure.


Recommended Reading: Snap On Technical Training Systems, Air Conditioning, Basic Service Training Series, pn ACT279B, Mitchell International

Thank you very much for the guidance. I will check again tomorrow and adjust if required. Where would one buy or access that manual?

OMG......sell the car

Piss off.

ahhhh, no sense of humor!