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basic a/c question

Applekrate on Thu September 06, 2007 4:37 PM User is offline

Year: 1972
Make: Pontiac
Model: GTO
Engine Size: 455HO
Refrigerant Type: r12

I just found this forum and have been going through it for a few days. I went back to page 15 to see if my question has been asked or not. I am a regular gear head type of guy and I do most everything on my cars from paint to building my own engines, electrical, etc, etc.
I need to learn more about a/c function. Everyone has their opinion, and it is difficult to get a straioght answer at times.

I would like to ask this- What is wrong with r 12? It seems the world is switching over to 134 in the last 10 years or so. I remember when the requirements for 134 came out ( mid 90s?). Everyone made a rush to retain their r 12 because it was 'superior'. Now, it only seems to be used by the die hards.
I realize 134 costs less but, r 12 has come down considerably recently too.
I also realize and have read that 134 works better with a certain type of condensor, etc

But, in comparing the 2 options- R12 and 134a..., all else equal, which is better, colder? r 12 or 134a?

Thank you AMA for providing this forum. I will buy from you when I need something.
Steve



TRB on Thu September 06, 2007 5:41 PM User is offlineView users profile

I'll leave the scientific explanation for the engineers.

Both work very well when using the correct components for said refrigerant. R12 has a bigger margin for error so you may get away a smaller component I.E condenser.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Chick on Thu September 06, 2007 6:58 PM User is offlineView users profile

Google montreal protocall9sp) and if you have a few hours to read [email protected]#$t it will explain and confuse you more. R134a is also scheduled for phaseout, so don't get to attached...
R134a phaseout time tables and other useless info

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

bearing01 on Thu September 06, 2007 10:08 PM User is offline

R12 is a CFC. The chlorine atom breaks off and acts as a catalyst (never wears out) to forever break down the ozone layer. It is blamed for putting a hole in our ozone, forcing us to wear sun block.

R134a is an HFC. It uses Fluorine instead of chlorine. It doesn't eat the ozone, but acts as a green house gas. Everyone is trying to reduce carbon dioxide green house gas to help prevent global warming. The future will phase out R134a because it's a green house gas.

To my knowledge, both have similar heat transfer characteristics. The difference is that you need to use higher pressures (physically larger compressors) to get the R134a to work.

As for A/C operation....
To get a liquid to evaporate you need to raise its internal energy by adding either work or heat. Liquid takes in heat to evaporate. To get a vapor (gas) to condense to a liquid the vapor has to get rid of its internal energy (its heat). If you could get a liquid to evaporate in a cool room (72*F) but then take that heated vapor outside where it is hot (100*F) and some how get it to condense to a liquid outside in the heat, you'd have an air conditioner. The problem is the condensation process would require the energy (heat) to be removed from the gas out in a warmer area. This is reverse to what will happen in nature. But, if you put a compressor in the system and get it to do work on the system then you can get the system work reverse of nature and in your favor.

Liquid in cold room (R134a inside car's evaporator) uses room heat (at 72*F) to make liquid R134a evaporate into vapor.
Pump will take that vapor outside where it's hot (100*F) where it won't condense naturally. However, the pump compresses the vapor to raise its pressure until it turns into a liquid. Raising the pressure will raise the dew point temperature of the vapor to something higher than outside temperature. This will cause vapor to turn back to liquid inside the car's condenser placed in the outside heat. Turning back to liquid means R134a got to give up its energy (its heat). The condenser gives off this heat. The hot liquid will then pass through the expansion valve where the liquid's pressure drops. Inside, the drop in pressure gives the R134a a dew point temperature much lower than the inside cabin temperature. That means the liquid will evaporate to use up more inside heat. And the cycle continues.

There's actually a lot of thermodynamic theory involved. But that's it in a nut shell.

You got to compress R134a to a higher pressure (like 220psi) in the 120*F heat & humidity than say R12, that only requires say 150psi, in order to get it to turn from a vapor to a liquid. more psi means more hp and work. You also need a better condenser coil to get rid of the heat more effectively.

Edited: Fri September 07, 2007 at 10:43 AM by bearing01

Applekrate on Fri September 07, 2007 12:38 AM User is offline

Thanks for the replys. More would be appreciated too.
So if I am interpeting this correctly.... r12 and 134a are the same, or as good, as each other for cooling. Just 134 needs more pressure and a better condensor to equal r12?

If this is true, then what if you put a better condensor with a r12 system? Would that make that system colder?


To rephrase my question in a nutshell- Which system can be made to blow colder? r12 or 134?

Thanks again. I am learning.
Steve

Chick on Fri September 07, 2007 5:57 AM User is offlineView users profile

That really doesn't apply to Auto AC systems, since you will find Home freezers that work with R134a, chillers, window units etc..It's how the system is designed..I have been in R12 vehicles that worked great, and some not so great, also cars with R134a systems that you couldn't let the air blow on you (would burn your skin) and others that you'd be better leaving the wondows down (exaggeration) but don't forget, interior area, amount of glass, color of vehicle, insulation all play a role in how cold the interior is..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

bearing01 on Fri September 07, 2007 11:16 AM User is offline

I believe an R134a system designed today for R134a can be just as good as an R12 system designed for R12 back in 1985. However, if you put R134a into an R12 system (do a retrofit) then the system won't work as well because you're using R134a in a system designed for R12.

I also believe today's AC system design strategies are different than in the 1980's. Back then they didn't care about emissions. Now they do. Also, you don't want to loose unnecessary engine hp to drive a compressor. Efficency and reduced emissions are the design targets today. Face it. 90% of the cars will end up in a junk yard some day and most of the AC systems will get discharged to the atmosphere. If you could reduce the amount of refrigerant used in the cars then you would reduce the automotive AC emission problem by half. Nowdays the AC systems are designed to use less refrigerant than yesteryears's AC systems. That means the system has to be more efficent in order to get the same amount of cooling. Improved evaporators and condensers ensure better heat transfer from the reduced quantity of refrigerant. Also, higher efficent compressors mean less engine Hp loss and better fuel economy for less CO2 emissions out the tail pipe.

It's not that they can't make the R134a systems "colder" than the older R12 systems, but now days they only make them as good as they need to be. Sometimes I guess their performance comes in just under par.

Edited: Fri September 07, 2007 at 11:19 AM by bearing01

iceman2555 on Fri September 07, 2007 5:17 PM User is offlineView users profile

OPPS

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson



Edited: Fri September 07, 2007 at 5:20 PM by iceman2555

TRB on Fri September 07, 2007 5:24 PM User is offlineView users profile

Quote
Originally posted by: bearing01
It's not that they can't make the R134a systems "colder" than the older R12 systems, but now days they only make them as good as they need to be. Sometimes I guess their performance comes in just under par.

Bet that is why some claim there is two sets of tooling for compressors. Guys like Iceman only get the good stuff.

-------------------------
When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

iceman2555 on Fri September 07, 2007 5:34 PM User is offlineView users profile

Perhaps, a miss reading of bearing01....but are you stating that the compressor increases pressure/temp of the refrigerant and thus results in a change of state.....gas to liquid....However, the pump compresses the vapor to raise its pressure until it turns into a liquid
Perhaps, these ole freon scarred eyes are miss reading this statement. The compressor does compress....raise temp...but not a change of state....that is the cooling job of the condenser.....cool refrigerant.....condense a gas=liquid......
AnyWHOOO....for Applekrate....An R12 system will always work (cool) better with R12....but a true designed and functional 134a system...cools pretty darn good.
Retro's are a 'n'other' story altogether.

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

BugMan on Sun September 09, 2007 11:18 AM User is offline

In general, R-12 is more much efficient than 134a and is the reason it has been around for so many years until EPA got involved. Simply put, it takes less work to achieve the cooling effect (BTUs). IOW, R-12 operates at lower pressures than 134a to get the same evaporator temps.

I'm not sure that the price of R-12 has dropped or not, but there are drop-in replacements (406 or 416...I think). This may initially drop the price of R-12, but I've heard back and forth discussion as to whether the drop-ins do as good of a job.

iceman2555 on Sun September 09, 2007 9:57 PM User is offlineView users profile

Gotcha second line....thinking of adding a 'third' line for those special customers.....those that prefer those with stange writing on the label.....ahhhsooooo

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

NickD on Mon September 10, 2007 8:04 PM User is offline

Quote
In general, R-12 is more much efficient than 134a and is the reason it has been around for so many years until EPA got involved. Simply put, it takes less work to achieve the cooling effect (BTUs). IOW, R-12 operates at lower pressures than 134a to get the same evaporator temps.

Actually, the opposite is true, both the specific and latent heat of R-134a are greater than R-12, or stated in a different way, a given quantity of R-134a has greater capacity to carry away more heat than R-12, and since this ability is greater, less pumping energy is required, therefore the efficiency is higher.

A problem is encountered by putting R-134a into an R-12 system, first off the condenser cannot handle this extra heat that results in much higher temperatures, R-134a also does have about 10% higher pressures that is compounded by the condenser and cooling system to handle this extra heat, so the pressures are much greater than expected. To compensate for these higher pressures, not as much R-134a can be put in, so rather than having a pure liquid, more like foam, and foam does not carry heat away like pure liquid. Efficiencies are also very dependent on the pumps ability to pump without eddy currents and undo restrictions plus the plumbing of the system to minimize restrictions, the only permissible restrictive device should be the orifice itself.

Efficiencies of an R-12 system can be improved vastly by installing a parallel flow condenser with additional or larger cooling fans, then you can get some pretty decent cooling, but we are talking about putting bucks into a vehicle that is already over 13 years old. Probably okay for a restoration job, but not something to take you around the block one more time.

I prefer sticking with R-12 for my R-12 vehicles for that reason, both cost and in one case, for purity. Regarding the cost of R-12, still still fill the system cheaper than filling the tank with gasoline, except the R-12 lasts was longer than the gas. Gas tank seems to go on empty just by driving around the block a couple of times. Come to think of it, the price of R-12 was always less than a tank of gas. Dang, just put in 40 bucks for gas, could fill the AC system for around 27 bucks, but it doesn't need it.

Applekrate on Mon September 10, 2007 11:17 PM User is offline

I appreciate the replys here and I am learning much. I want to be able to do most or all of my own a/c work with both kinds of 'freon'.

However, there seems to differences of opinion here as to which is better. I would still like to know....all else equal, which can be made to blow colder? regardless of whatever parts I would use?
In other words, if you had 2 ideal systems. Ideal meaning the best, most efficient parts in each system. 1 with r 12 and other with 134. which could be made to blow colder?

thanks again all you guys for the replys.
Steve

NickD on Tue September 11, 2007 6:15 AM User is offline

33*F seems to be the limit for MVAC unless you live in a very dry desert, sitting next to a freezer that uses R-134a and it's at -12*F, is that cold enough? But my refrigerator uses R-12, Amana figured that is more efficient than R-22, it's freezer is set at -10*F. Never was much of a PAG fan, substance is the same stuff used for women's makeup, but you have BVA-100 that doesn't have the moisture problems of PAG that works great with R-134a. Can walk into Wal-Mart and buy a can of R-134a, can't do that with R-12 and you don't know what's going to happen to R-12. Ironically, many new HVAC systems are still using R-22, a mild form of CFC's and with all this BS on global warming, they are sure to pick on R-134a, but at least for now, you can buy a couple of 30 pound tanks for a couple of hundred bucks, that should hold you for awhile.

I would go with R-134a and BVA-100 oil, like the V-5 even though that means even buying more tools to change the bearing, V-7 has more output. Would be nice if they could be mounted off the ground, probably would last longer if you are forced to drive in salt slush.

jaym on Tue September 11, 2007 7:46 AM User is offline

Being inexperienced, please explain ".....V7 could be mounted off the ground....." and the reason it couldn't be mounted there.

TIA.

NickD on Tue September 11, 2007 9:09 AM User is offline

More of a problem up north in the road salt area, GM use to mount their compressors way up high on the engine, easy to get to, now on many vehicles are mounted way below where they are exposed to winter road salt leading to corrosion or belly leaker problems. When mounted high, weren't exposed to that road salt slushing so would last much longer. Just a small point.

bobbyrae on Tue September 11, 2007 6:56 PM User is offline

Quote
However, there seems to differences of opinion here as to which is better. I would still like to know....all else equal, which can be made to blow colder? regardless of whatever parts I would use?

In other words, if you had 2 ideal systems. Ideal meaning the best, most efficient parts in each system. 1 with r 12 and other with 134. which could be made to blow colder?

Steve


R-12 has somewhat better heat transfer capabilities, since, as people keep saying, you need a little higher system pressure and/or larger condenser for R-134a to acheive the same heat transfer. And more heat transfer means COLDER. I think your question is basically unanswerable when you ask which could be made to blow colder. Either one could be modified radically to achieve a very low temp, but at what cost? You can always increase the pressure and size of the exchangers. They design R-134a systems to achieve the same temp as older R-12 systems. Your question is like asking which engine can produce the most power - gasoline or diesel? It just depends on the design, but we know that diesels generally are more powerful.

But I think that for most of us the big question is whether to convert your old R-12 system to R-134a. I initially thought I would do that, but after investigating, realized that it would be more expensive and less effective. Since you can still get freon (R-12), the simplest thing to do is just fix the old leaky system and put some R12 in there.

Test Specimen on Fri September 14, 2007 3:32 PM User is offline

I have no idea where all the mis-information on R-134a and R-12 comes from. Most of the 'common' knowledge is incorrect. R-134a and R-12 are both very good refrigerants, both can work very efficiently, and picking which one is better is like trying to figure out which color goes best with white. It depends on what else you are doing.

The increased heat transfer performance of R-134a almost exactly cancels the reduction in performance by the increased condensing pressures. Bottom line is the performance differences between the two refrigerants are a wash.

Here is original research from NIST, one of the most respected testing organizations on the planet that did science to show what the correct answer on heat transfer is:

http://www.bfrl.nist.gov/863/HVAC/pubs/PDF/NISTIR5144LubBoil.pdf

Check out the abstract where they state R-134a has a 20% higher heat transfer coeficcient than R-12. Adding POE lubricant to the R-134a actually increased the heat transfer coeficcient of R-134a some more. The same thing does not seem to happen with R-12.

The OEMs that designed equipment did a lot of work on energy efficiency and cooling performance and found almost no difference in properly designed systems. The differences were so small as to make measuing differences almost impossible (a few percent either way can't be measured). As a practical example, the energy efficiency of a modern R-134a refrigerator freezer is at least 30% higher than the old R-12 units - they had no trouble squeezing out more performance when they had to - they could just as easily have done the same with R-12, and probably for the exact same same cost.

If you get different information from this, I suggest you look up the original source of the data and check it against high quality science work to see how it stands up. I'm betting you will find the quality of the scientific work that shows R-12 to be significantly better than R-134a is suspect.

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