While the naysayers are on the other side of the fence I still content that less than $400 can put your system in the Lexus A/C cooling class.

1.) Yes, convert to R-134a.

2.) add a trinary pressure sensing switch to the high pressure side.

3.) Use the switch to control the on/off cycling of the compressor.

4.) Mount at least 2 fans to suck airflow downward through the rear lid condensor as controlled via the pressure switch 2nd function.

5.) Use a TDR, Time Delay Relay, to allow those fans to continue to run under the control of the 2nd pressure switch function for up to 10 minutes post engine off.

6.) A reasonable, legal, tinting of the side and rear windows will always be of help.

The primary function of the pressure switch will be to prevent the compressor from "over-running" and thus over-pressurizing the system. The secondary pressure switch function will prevent the over-pressurization of the system due to latent engine heat.

I'll have to go buy a thermometer to put in the vent to test it. There seems to be enough of these posts that it would be cool (double entendre!) if we could get an idea where all the various setups stand. I'm a data nerd, so knowing what the starting interior temps is, and then the vent temps through 15 minutes would provide a nice graph from which we could extract a lot of data from. Weaker systems will have a smaller differential than more powerful systems. From there, it would be a lot easier to help people get the most of their money. Maybe some folks are ok with a bit of elevated temps at the stop lights, and just want something cooler for the highway. And others will want meat locker temps in stop and go traffic. Nothing wrong with either approach, but there will be a big difference in coin spent.

I'm in the middle of installing my new Kuehl setup from Griffiths and went through the same process as you a few months ago - trying to balance what I wanted to accomplish with the costs. What I knew I didn't want to do was have to keep playing with the system, incrementally trying to get to what I wanted.

With that in mind, I figured there was little point in re-using components that were now 31+ years old. The A/C in my car hasn't worked since I bought it 12 years ago, and I suspect it stopped working long before that so why try and make this old crap work again?. So I went with all new components except the rear deck-lid condensor, including the rear fender mount condensor. For good measure, I also decided on a new Wirbelsturm evaporator motor to push more air, as well as the Kuehl fan switch and center vent replacing the bowtie. Replaced the thermostat switch as well for good measure.

At this point in the installation, I can tell you that the evaporator motor and switch upgrade alone rock! Just having a lot more volume of air moving a lot faster at you makes a nice difference. Once the A/C system is charged and working, I have absolutely no doubt that I am going to be a lot more comfortable in the car.

I've got the new evaporator (incl fan and switch), front and rear Kuehl condensors, and driver side hoses all installed. Still have to hook up the new Kuehl condensor electrics, evaporator in/out hoses and compressor, so I've probably got a couple more evenings to put into it. Then I have to wait for warmer weather to get it all charged up - and will post results if anyone cares to see them.

So, my opinion would be if you want to try and do it in stages, at least start with new basic components (evaporator, front condensor, R/D and barrier hoses at least) so you know you've got a system with integrity. Adding a kicker fan to the rear decklid condensor would probably help too. The new evap motor and switch can easily be done after you've dealt with the basic system (make sure you use screws to reassemble the evap box). If you find that it's still marginal you could then add a rear fender mounted condensor.

I figured that trying to re-use anything 30+ years old was a false economy that I would regret and pay for again at a later point anyway, so that allowed me to throw out any budgetary constraints!! I prefer driving and playing golf to being a home mechanic so I wanted to do it once and get good results I'd be happy with.

No. Vent temps, LOW vent temps, are really only important during initial cabin cool down periods. Once that is accomplished(assuming it can be) a vent temperature just a few degrees below your cabin atmosphere comfort level will suffice.

At least that's the way ALL modern day climate control systems operate in automatic mode, Lexus (NipponDenso), Ford, most US marques, (Denso US), and Porsche (Bosch) inclusive.

Exactly. I mean, you're looking at a baseline - probably 6-700 bucks for a bare bones setup. But, some extra coin to do it right means years of comfortable driving without the headache of trying to fiddle with things to make it work.

So, where does one source a binary/trinary switch? And how would one put that switch in their system (is it an inline switch, or does it break off at a connector?)

WWest
Unless your car seals a lot better than mine, has tinted glass, a lot more/better insulation, more evaporator fan CFM, and an overall better sealed car...vent temps need to be quite cold and remain quite cold to keep occupants comfortable on a sunny, 100-degree day.

Just because a modern car is in an "automatic" mode does not mean the vent temps are not very cold.

Assuming a person does not build a different evaporator/fan and increase CFM to the vents, vent temp is the best measure of performance of system upgrades...as other variables remain constant other than ambient temp/humidity.

TO r-mm........ Guy asks a fairly simple question as a newbie and all of a sudden it is a pissing contest over kuel and wwest. Perhaps we can help this guy without all the drama !!

Intentional or unintentional irony?

Griff can get you fixed up.

Wwest, without starting a pissing contest here, let's be logical because there are people reading what you post whom seem to have much different opinions and experiences in life and than what you are trying to 'project':

1) The quickest way to cool down a hot car cabin, for example the cabin of the car that has been sitting in the 95F sun for 4 hours and has reached a typical interior of 120F+, is move that 120F+ air out quickly as possible. So, if it's 95F outside and you roll down all the windows and drive away, that would replace the 120F+ air with 95F air the quickest. There is no evap fan on this earth, lol, well maybe other than the Wirbelsturm which can exchange the air so quickly.

2) Assume you have 1000 cfm of 40F air vs. 100 cfm of 32F air, which will make the cockpit more comfortably .... quicker?

That will only be the case if the "heat gain" (what is being absorbed back into the cockpit by the outside ambient and radiant energy the sun is dumping through the windows and thin R value above your head) is not greater than what the ac system can remove.

I disagree and frankly I think some 'modern day systems are a joke. My 05 Treg in automatic mode starts off with a blast, full fan speed, of what ever is in the vent system and what ever the evap core is at, and 120F+ of heat hitting is not pleasant. PS. Porsche is no longer "Bosch" inclusive for some time.

Female Trinary Safety Switch For Electric Fans - A/C Pressure Switch

Then why do ALL porsches of the era of concern have the control ability to RAISE the vent temperature...?

...

You're missing the point. If your car can't make cold air, then it's not a powerful system. If you want to measure an AC system's ability to make cold air, you measure the vent temp. After the car has cooled, it's up to you to make yourself comfortable - either by reducing the fan speed and keeping a cold temp, or raising the fan speed and going with a warmer temp.

If you have a giant fan pushing cool air, sure you could achieve the same results as cold air moving slower. But, we're all working with the same fan - so it's not a factor. Vent temp is going to determine whether you have a strong AC system or not.

I own 2 Lexus, a Cayenne, and a Toyota 4-Runner...all post 1990. When was the last time you posted without a backhanded insult?

*snort*

From another thread...this is what you are looking for:

This is what I'd love to see wwest post, but it seems it's either far too complicated, or far too embarrassing for him to do.

I feel that I should bring up the point that vent temp is not really as important as the maximum delta, inlet air temp vs outlet air temp, that can be attained for a given system working with a specific air volume.

ALL, ALL, modern day automotive climate control systems, or more "simple" systems with automatic temperature setpoint control, operate the A/C cooling system 24/7, with a few exceptions, primarilly not below ~33F. The resulting system air outflow would be pretty discomforting were it not for the system's reheat/remix path, used to MODERATE the air outflow temperature to a level that only sustains , barely, the cabin atmosphere nearby your selected temperature setpoint.
....control

And that would be germane if you had a source of colder air than that inside your car when driving around when it is sunny and 100F outside...in which case, you would not need air conditioning.

...maybe a window airconditioner and a very long extension cord would do the trick.

The statement makes perfect sense. We are discussing potential sytems for pre '90 911s, not 2014 Lexus. They are somewhat different.

PM me your address, and I'll send you temp prove to stick in your vent. It seems you're either too poor to afford one, too scared to share the results, or maybe you don't even own a 911. If you can afford a prob, you have the knowledge to use it, and you own a 911 - then being a troll is the only other reason you wouldn't post this info.

Argument simply for the sake of argument...

If you don't understand then simply say so.

A good measure of an A/C system's cooling capacity relates to how different, how COLD, the outflow air will be vs the inlet air temperature at a specific airflow volume.

How cold will that room temperature, 72F, gallon of milk get for each minute left to chill in a 'frig...?

An idiot statement if I even saw one.

You and I both diverged from the current subject, pre '90 911s, to post 1990 products.

"..They are somewhat different.." Yes, different in the manner I stated, to which you jumped in and disagreed, falsely.

I think we have a winner.

I assume you wish to know my vent temps starting with the cabin preheated, fully preheated, HEAT soaked, to a specific temperature. Tell me which and if it is within reason I'll provide the initial vent temps, along with how long it takes the system to bring the cabin atmosphere down to 72F. I'll also provide you with the climatic conditions under which the test is run, OAT, Rh, and an estimate of the heat gain form the sun, if any.

Okay..?

blah-blah-blah,..no data testing points. Until that;s provided , you are dead in the water, WWEST. And I do mean truly dead. Quite tiresome with no test data.

Best,

Doyle

How many car owners with a stock AC system in a pre 1990 911/912/930 can say that?

Gentlemen, show of hands?

I am also an engineer...I suspect I understand as well as you...or better.

Explain why that is not the same as vent (outlet) temperature at a specific ambient temp (input) since the ductwork (air path) and evaporator fan are fixed (volume)?

If you don't understand, them simply say so.

Because ambient temperature, OAT, is NOT an input to the recirculate ONLY mode of the Porsche 911 pre-1990. While OAT does not change as a function of the duration of A/C operation, IAT does.

Evaporator fan are fixed (volume)...not in any of my 911s,

you, of all people, do not understand....?

The amount of cooling a given volume of air receives, temperature delta, upon each pass through the evaporator is a reliable measure of he system's cooling capacity.

Take the temps at whatever cabin and ambient you like. Just make sure to record what those temps are. We're not going to get a perfect lab setup, but knowing it's 85 degrees outside, high noon, sea level, 75% humidity, and the inside of the car is 90 degrees, well that will provide plenty of context. Take some vent temp readings when the inside is still steaming hot, and after it has cooled down. Make sure they're at idle.

LOL, nice. I don't believe wwest has any kind of science background. Or he does, and is TROLLING.

IAT does not change appreciably enough to make much difference...and is effectively OAT unless the vent temp is quite low and volume is quite high. If you start at 100F...a trickle of 65F air will not even overcome the engine heat and the sun coming through the windows. Most folks drive their 911s for an hour or two at most. The rate of change would never make a serious impact. If after 8 hrs of driving my 100F interior drops to 98F...I am not impressed.

The max volume of air is fixed on all my 911s. It is on yours as well.

Yeah, we've only been saying this for about ten threads now.

This doofus kills every damn AC thread there is by trying to shout down anyone who actually knows anything about these systems.

He's splitting hairs. The interior temp of the car is going to be much higher than the OAT, initially. 140-150 degrees F around here, in the summer. The big delta is opening the windows for a couple of minutes to get that super-heated air out, and to begin cooling all those IR-absorbing black materials in the car. All the while, the AC is running, and cooling the ductwork. Close up the car, turn the fan on high and let the Griff's evap fan blow hard on that higher-capacity evaporator. The interior temperature drops very nicely when the output air is 45 degrees at the highest air volume. Pretty soon, you have goosebumps and have to turn the air and the AC down a touch. The car is still at about 80 degrees, but the evaporative cooling on your skin is now in effect. And 80 is better than 140. Soon, the fan is at it's lowest speed, and the AC is set at the speed next to "off", and the air coming out of the vents is 35 degrees, and the interior temp is about 70, and steady.

He implies that vent temps are not important. Of course they are. It is not rocket science...I can park my two targas side by side at 95F ambient. Open the windows and IAT=OAT. One Targa has a 33F vent temp and the other 56F. One is comfortable almost immediately with the 33F air blowing on your body. Eventually you will begin to see some effect of the system cooling already cooled air. The other targa never gets comfortable. You can drive cross country and it will never cool down the interior if there are 100F+ temps. That is why vent temps are so important. If you can only drop IAT by a degree or 2 per hour...it is negligible unless you are driving cross country...and even then, it heats back up to ambient if you stop for gas.

When he specifically posts that he has tested his add-on fans and they will duplicate the performance posted above (which is what I would expect from an A/C system): "In 95F ambient air temp with full sun (over 300 shortwave insolation) system produces copious amounts of 40F air at high blower setting and a steady flow of 32F air at medium blower setting."...then he will be interesting. Until then...he is just tilting at windmills (and folks with well-designed, proved products). No one is looking for half a solution.