Decent 911 A/C is possible
 

FIRST AND FOREMOST I do not want to start another Pelican A/C brawl.

I am very pleased with my results, there are many different ways to get desirable A/C results, many vendors, many philosophies.

In a nutshell, my 1975S had a dealer installed under dash system installed. The system was removed during the engine swap. In 2013 I completely reinstalled the system adding a front condenser and blower fan. The car has non barrier hoses and all used OEM hardware. In 2 years I have had to add 1/2 a can of R134 due to 1)Hose leakage or 2)Connection leakage 3) or both

On 85 degree (low humidity) Southern California days I can initially get sub freezing temps
http://forums.pelicanparts.com/uploa...1439685008.jpg

After 30 min of freeway driving the temperature rises to 32 degrees

http://forums.pelicanparts.com/uploa...1439685117.jpg

Eventually vent temps riding to high 30s low 40s

Today it was a scorcher in Southern California so I thought I would give my system a real test.

I taped a wireless temperature sensor to the front bumper and took the car out for a spin

Initial temperatures were outside 105 f vent temp 32.9 f

http://forums.pelicanparts.com/uploa...1439685416.jpg

After 30 minutes of freeway driving, indicated outside temp 107, vent temp 42.8 f

http://forums.pelicanparts.com/uploa...1439685561.jpg

For now I will leave well enough alone, but if I ever have to open up the system I will definitely upgrade to newer better designed hardware.

I realize these results would be much different in the humid south. Some of you may notice the thermometer in the ash tray indicates 87 degrees in the interior of the car. During the test I had both windows open 1 inch due to a bad targa seal.

Again I hope this thread does not deteriorate to a hate fest. I just wanted to share the fruit of my 2 year project.

Thanks for listening

Bottom line seems to be, if you want the possibility of functional AC, a coupe would be a good choice.

Yes the additional surface area of the glass does increase the cabin temperature.

But it isn't unbearable. Tinted windows would help

Outstanding write-up. Congratulations. Job well done.

Additionally one of the wrestling points in past AC threads has been sub freezing initial temps and no one has taken it beyond sitting in the garage for metrics. Wonderful job.

That is a funny joke, Stig. Thanks.

Here is my write up from 2013 right after the install

http://forums.pelicanparts.com/porsche-911-technical-forum/758727-reinstallation-911s-c-love-story.html

Thank you so very, very much.

Was a bit puzzled as to the rise in vent temperature but the open windows probably the cause.

Hmm, I thought the rise of vent temp over time would be due to a warmer refrigerant 40 minutes after turning system on vs. the cooler refrigerant immediately after turning the system on.

The open windows merely prevented the cabin from achieving maximum cooling

That is my lay analysis

Driving typically involves sustained higher RPM ranges which should add to condenser efficiency, plus more pump volume, so seemingly the vent temperature should declined or least remained stable.

Yes perhaps, but in my case I am in the slow lane doing 65 at 2200 rpm (ish).

Perhaps more spirited driving (and engine RPMs) will get me the higher pressure/pump volume

RNajarian,

Nice write up.

A 10F rise in vent temp could be the evap core is starting to ice "partially", reducing
the effective surface area of the coil.

To take that supposition out of the possibilities, when it happens again quickly
pull over to safe place, leave the system running, pop up the front trunk, pull back the carpet, open the smuggler's box lid and see if the evaporator outlet pipe has iced up.
If so... the easiest quick fix is to turn back the thermostat a few clicks.
The thermostat should turn off the compressor clutch at some point moving CCW,
if it does not, keep turning it to full CCW, if the compressor stays on then its time for
a new thermostat (I just had a client drop off a basket case of parts to put in his car
and his 'new' old stock thermostat was shot; always on. )

I've always believed/thought A/C in a 911 was "decent",(heck, even darn good at times). I've never been one to delete or remove it if it's there. Thank You for sharing your thoughts on this too

Never thought of doing this, GREAT suggestion!I'll give it a try.

One of the next upgrades I will do is put a more robust fan on the front condenser. The current one puts out 150 CFM, there are several units out there which are more capable than my current one.

Again thanks all for the input

Your experience and mine are similar. I ended up buying all my own AC tools, pumps and gauges back in the 80s when the 'pros' were worthless at fixing even basic AC issues with the even easier to work with R12. There is so much hysteria surrounding vehicle AC it is ridiculous and even more so with air cooled 911s.

When you have AC questions, kuehl's your guy. Do not pay any attention to wwest.

A lot of people have asked me why I did not go out and buy all brand-new hardware when I first reinstalled the system.

The reason I did not was because I was nervous after reading all the negative reviews about the 911 AC system to go out and spend for $5000 on hardware which would give me mediocre results.

So my intent was to install a inexpensive AC system and see if good results were possible.

My lay opinion is that good 911 AC is possible, of course it matters where in the country/world you are located. High humidity areas such as the US South will have different requirements then say the more temperate areas of Canada. This is why some systems may require two front fender mounted condensers and others can get away with simply the one under the front valence. Some systems may require additional cooling through a rear decklid fan.

My hardware is tired, it is old and the design is 30 to 40 years old. The newer hardware have much more efficient designs and much more modern materials. I do plan on replacing my hardware as they fail over the years. But for now I have an adequate system and I'm still figuring out the best way to optimize it. One of the things I did which made a big difference was adjust the rear deck lid to improve the airflow through the rear condenser.

One thing I feel that is very important to note that when I initially reinstalled the system I was very careful to ensure all the hardware was clean and all the connections were airtight I used a new larger receiver dryer and I pulled a vacuum and kept it for over a week to ensure the system integrity.

An additional item I need to do on my car is complete the Targa top and ensure proper sealing of the cab. When I do that it would be curious to see how cool I can get the car on the hot summer days.

The next items I think I will be upgrading on my system is a fan/blower for the front condenser and I know I will need to break open the system and replace the evaporator, schrader valve and thermostat. I just don't really have the stomach for that right now.

In my unprofessional opinion the Bottom line is the 911 is capable of decent AC performance the only caveat is that it is not a one-size-fits-all option. You need to carefully designed your AC system for your car and your climate.

But admittedly it is a fun project to do for us weekend warriors. Thanks to all the Pelicans who have helped me and given me guidance through the years I could not of done it without you

Congrats Brother. Yeah. mine works great too thank goodness these past couple of days in L.A. traffic was a killer.

Enjoy Brother! Let me know if I you need a hand sealing the targa, I can lend my un-pro hand :-)

Thanks Pal, I may just give you a call

Of course OEM 911 AC is good enough for you! You live in Canada! http://forums.pelicanparts.com/suppo...eys/spankA.gif

Spend some time in South Texas, say July through September, around 5 PM and see if it'll suffice.....:eek:

:D

Another scorcher today in L.A. Took the car for another whirl, temp rose ~10 degrees as before, pulled over as you suggested . . . And voila the outlet pipe was frosty.

Likely on the way to a complete freeze up.

Maybe time for one of these

http://forums.pelicanparts.com/uploa...1439753387.jpg

any one wanna help put it in? 👍

Before you do that how do we make sure your's isn't dirty and crudded up...?

Check through the passenger side inlet?

Post #589

http://forums.pelicanparts.com/porsche-911-technical-forum/823307-my-ac-burns-me-up-help-30.html


How do we go about confirming, or not, that the increasing engine/exhaust/catcon heat isn't causing the lost of rear lid condensing efficiency due to IR heating..?

First, follow CG's instructions, turn the thermostat CCW until the compressor clutch circuit opens, shouldn't take more than 10-15 degrees.

If the thermostat's max cooling position isn't "calibrated" to cycle the compressor off in the conditions you stated, "frosty pipe", the high side will be extreme and will PUSH more refrigerant through the ("never fully closes") TXV than its design specs call for.

Prove it.

This is mine. Totally stock 89. Just purged and charged r12. Posted on rennlist too. Anyway this is about 90 outside temp on highway at 70mph and running on level 2 for about 30 minutes. Keeping the cabin cool for sure. Hot this weekend! I'm in SoCal.


http://forums.pelicanparts.com/uploa...1439768146.jpg

What??

Wow, here I am restating, echoing, CG's statements and you say...


PROVE IT!

Ask CG....SmileWavy

If you are going to consider tinting, then look at 3M Crystaline. It provides better heat mitigation and is not dark colored like other tints. Should you ever decide to install it, make sure you find an authorized 3M installer that will provide a warranty. 3M has a lifetime warranty on the product as long as it is installed by an authorized installer.

Supply links and quotes.

It is expensive, both the product and the installation.

[QUOTE=RNajarian;8755478]Another scorcher today in L.A. Took the car for another whirl, temp rose ~10 degrees as before, pulled over as you suggested . . . And voila the outlet pipe was frosty.

Likely on the way to a complete freeze up.

Maybe time for one of these

http://forums.pelicanparts.com/uploa...1439753387.jpg

any one wanna help put it in? ��[/]
I put the thermostat around 1 on the highway and 2 around town. Keeps it in the hi 30s.
In Redondo beach now, just visiting, sooo dry compared to south Fla.!

Driving around Palos Verdes today Draco! Didn't see you ��

You do not have to 'calibrate' the stock thermostat.
You just have to have the probe located properly in the evaporator.

I got a quote of ~$600 for my car (coupe). I don't know how that compares to other tint products.

I haven't done it yet but am considering it.

BLUF (Bottom Line Up Front)

• You can only run your system as cold as where the thermostat switching the compressor on/off regularly or you will see icing, unless you are in a very dry climate.
• When the compressor shuts off during normal cycling behavoir I am seeing a 10-15 degree increase in vent temps. This happens faster than an "Expansion Valve/Icing" situation (as described below). During the off cycle any ice built up on the evaporator melts off, as the evap temp rises well above freezing.
• On the freeway you can run colder thermstoat settings, and still have the compressor cycling, than you can around town.

I am a little late to this, and having just gone through a rather painful (and successful) A/C rebuild (which I will do a write up on soon) I thought I would chime in on issue I was having with my new system...which was vent temps slowly creeping....here is what I learned.

• If your system gets very cold, let’s say 42 vent temps, and stays there for a while but then starts to climb slowly…..and does not stop even as it passed through 65 (if you are that patient)…and the compressor is not cycling/shutting off for a bit....you have the thermostat/system to cold. The Expansion Valve (EV) is slowing the refrigerant flow to help prevent icing. However it cannot totally prevent icing (in my humid climate) and it opens/closes slowly. So the temp will just keep creeping up. This also causes the compressor to work harder as it is pushing against the closing EV. I call this an EV/Icing event. :)
• If you have actually iced the evaporator (as I have done a few times) you will notice less airflow out of the vents AND the temp creeping. I also noticed very little-to-no water dripping out under the car. If I let the system sit for 10 min and then turn it on water is POURING out of the evaporator, like a hose is in there.
• If I am on the freeway I can keep turning mine down to get high 30's-low 40's vent temps AND have the thermostat click the compressor on/off. This prevents icing and enables colder vent temps then when I am on 45 mph roads with stop lights etc (not stop/go traffic). This is because when the thermostat goes off, the vent temp will rise 12-15 degrees and does so more quickly then when the EV starts to close. This warmer air blows out any ice that has built up when the compressor was on, and really does not hurt the cabin temps. Sometimes I can smell the moisture, as it comes off the evaporator, as the system cycles in this state.

I could go on and on.....but what's the best setup for max cooling with no icing?

1. Find the thermostat setting that shuts off your compressor when your evaporator reaches 32 degrees. This will prevent icing and should give you pleanty cold vent temps.
2. On the freeway you can get evaporator temps below 32 without icing, AS LONG AS the thermostat cycles the compressor on/off regularly to let the system come up to high 40's-low 50's before kicking back on, as this will melt out any ice that may have built up each cycle. On slower roads though I have found this setting does not permit the thermostat to cycle in my climate, which then creates the EV/Icing issues described above. Once that issue is present I have to turn the system up (like almost to the warmest setting, to get the compressor cycling regularly again) pretty quick, or I get to a place where the temp just creeps.
3. I have learned that humidity DOES matter, contrary to what many so-called expert say. Here in Florida I cannot run evap temps below 32 for any real period of time without icing, PERIOD....unless I am on the freeway. At full cold, even on the freeway I can cause an EV/Icing event within 15 min…even when it is 100 degrees out. A friend in Az (no humidity) can get evap temps below 32 as he does hot have enough humidity to build ice, in fact he can get mid 30’s vent temps. My car can be pissing water like a hose where his will barely drip. Also remember the action of the EV may prevent the icing in non-humid climates, but I have not seen it be able to do so in my humid climate on many cars.

So how do I achieve the above noted condition?

1. I currently have a digital cooking thermometer sensor on the input line of the evap. This is the same line that has the Expansion Valve’s sensor (not the valve, the valve is in the output line), meaning the line in the smugglers box that gets water/ice on it. The wire is run back in the car so I can see the units display.
2. I have been driving down the freeway, turning the thermostat down until I get the 32 degrees...trying to find that point where it shuts the compersor off at 32. Once achieved I note that position as my "MAX" setting.
3. I then drive around town (not stop/go) to watch the evap temps. I need to ensure that around town it still cycles the thermostat at or just above 32.
4. IF YOU ARE IN A NON-HUMID CLIMATE (Az, Ca, Australia, etc) then you could experiment with colder settings below the one found above, again because your humidity is so low icing will be less of a problem.
5. I have heard that there is a refrigerator switch that could be placed on the input line or the evaporator. These switches apparently open at 32 degrees, which if connected inline to the wire that the thermostat uses to cycle the compressor, would switch the compressor off at 32, no matter your thermostat setting. This would prevent icing completely, and I may investigate this.

On my car I cannot get the thermostat TO the 3 o;clock position. There is will not cycle properly, even on the freeway. At about #4 on the dial (just above 3 o'clock) my vent temps are regularly in the low 40's....sometimes in the high 30's. I also have found that, for the most part, the thermostat setting that works well does not change as the outside air temp does. This makes sense as they thermostat sensor only cares about the evaporators temp.

Also remember that our cars are recirculate only. This means the lower the inside air temp is the lower the vent temp will be, to a point.

"If the thermostat's max cooling position isn't "calibrated" to cycle the compressor off in the conditions you stated, the high side will be extreme and will PUSH more refrigerant through the ("never fully closes") TXV than its design specs call for."

Nope, I never stated that, implied that or suggested that.

Weird!

SmileWavy

Duc/Chris,

Well done, excellent write up.

Adding an indicator light downstream of the thermostatic switch would make your procedure easier. A LED can be used if you somehow "squelch" the inductive voltage spike from the high Q clutch coil as the voltage is switched off.

PS: the metering valve, TXV, is on the evaporator inlet pipe, the "pigtail" sensor is on the outflow side.

..at some point..

And there is post #31..

"1. Find the thermostat setting..."

SmileWavy

Willard is trolling again.

{QUOTE}I put the thermostat around 1 on the highway and 2 around town. Keeps it in the hi 30s.
In Redondo beach now, just visiting, sooo dry compared to south Fla.!

Driving around Palos Verdes today Draco! Didn't see you ��{/QUOTE}

Fan speed or thermostat setting/position?

If you're getting high 30s in thermostat position one or two then you probably get freeze-up above 5.

Damn Good A/C in any case.

Always. :)

This is true....and I don't really need one as I can hear my new switch click on and click off, and unless I am on the freeway with the blower on full power, I can hear the compressor run.

I thought the TVX (EV) sensor was on the input line as that is the one that gets frosty...meaning it is colder???? The line with the valve in it never develops frost, meaning it is warmer...i.e. above the dew point of the trunk?

The pigtail sensor is used to "tell" (***) the TXV that the COLD has propagated to the outlet therefore the evaporator core is at the low limit that the TXV will ("should")allow.

The TXV inlet is exposed to "hot" (~105dF) liquid refrigerant and the outlet to vaporizing refrigerant. The "sum" is sometimes below dewpoint so you will often see condensate in parts of the TXV.

*** As the gas inside the pigtail cools more and more the TXV spring is able to overcome the gas pressure in the diaphragm and push the valve opening toward closing.

You might be confused by the EPR which is used downstream of the evaporator