Automotive Air Conditioning Information Forum (Archives)

blfastvette on Mon July 15, 2013 8:20 PM

Year: 1981
Make: chevy
Model: corvette
Engine Size: 350
Refrigerant Type: freeze 12
Ambient Temp: 72
Pressure Low: 35
Pressure High: 200
Country of Origin: United States

is there such a thing as a pressure chart for freeze 12?? i cant seem to find one. i have an 81 vette and it is like driving a magnifying glass, parrellel flow condensor, 2000 cfm fan bolted to it freeze 12, 72 ambient 200-210 high side 52 out the vent, would like to know what the hide side is supposed to be before i remove any gas??? also do different systems have different size orifice tubes with different results? i need to get my system squared away before i move back to the southwest

iceman2555 on Mon July 15, 2013 8:54 PM

Not sure why one would require a pressure chart for freeze12. Is this to be an attempt to charge a system with 'x' number of oz of refrigerant to determine charge rates? Since the premise behind freeze 12 was to mimic the pressures or r12...why not simply apply the r12 spec's. However, if one truly needs the chart check this web site. www.technicalchemical.com. It is available there.

Since freeze 12 is primarily 134a with a bit of another refrigerant...why not simply go with the tried and proven 134a. Forget all the hype about this blend.

Since the condenser has been updated to the newer performance unit....this should not be significant problem. Keep in mind that 'Vettes' always had AC cooling issues. Flush and clean the system thoroughly to insure proper amount and type of lubricant for the system and recharge with 134a. Start with about 90-95 %. See what happens.

Some of the later model Vettes had an additional electrical fan located behind the rad inside the shroud for additional cooling...does yours. If not why not mount a high flow secondary cooling fan in this location (plenty of room) and increase condenser cooling operations. A lower outlet temp of the condenser will result in a cooler evap.

Forget the hype of changing the orifice tube to the blue/red/purple/green/brown/whatever. True testing with test stands indicate that this does not contribute significantly to lower evap temps. The idea of adjusting the LPCO switch was proven to be bogus also. The pioneer of this technique actually changed his thoughts about this later after this process was introduced and stated that this procedure did not produce significant changes in evap temps. A adjustment of 2-4 psi to allow for longer compressor engagement would only produce an additional 2-3 degrees of cooling at best and often did not produce any changes. But if so inclined...go for it...will hot harm the system. Loss of cooling efficiency will occur is adjusted to low...the evap will begin to freeze..no air flow...no cooling.

The key is sufficient refrigerant to allow for proper cooling of the system. Changing the condenser in your vehicle was a major step in producing a properly cooling system. Stay with 134a and insure a proper and complete recharge and the system should work. Will it produce the temps you seek....that is dependent upon the insulation in the cabin of your vehicle.

Remove the carpeting from the vehicle and install Dynomat under the carpet. This alone will reduce the cabin temp significantly. Lots of heat generated by the cat right under the foot well...never mind the amount of engine heat that contaminates the passenger compartment.

Good luck

-------------------------
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

blfastvette on Tue July 16, 2013 11:35 AM

thanks for the extensive write up, i will keep all of this in mind when i go to lengths to get it cool in the car, i will need to be able to sit on las vegas blvd in comfort so i have my work cut out for me, you are right c3 a/c is inferior, more time spent on how the car looks then how it cools

blfastvette on Tue July 16, 2013 3:21 PM

i don't see where there is a pressure chart for freeze 12 at technicalchemical.com and it appears to me like the dont make freeze 12 anymore, this being said whose pressure chart should i follow, r-12 or r-134a?

mk378 on Tue July 16, 2013 11:07 PM

Get rid of the Freeze 12 and either revert to R-12 or convert to R-134a. Do not mix refrigerants. Besides being illegal, mixtures of different refrigerants almost always have worse performance than either one alone.

blfastvette on Wed July 17, 2013 1:09 AM

i have flushed and vacuumed the system, what is wrong with freeze 12? is it not better than r-134a?

mk378 on Wed July 17, 2013 10:08 AM

The only advantage to Freeze-12 is that it works without needing to change out the mineral oil. It's cooling effect is because it is 80% R-134a. Better results would occur with 100% R-134a.

Edited: Wed July 17, 2013 at 10:09 AM by mk378

webbch on Wed July 17, 2013 10:21 AM

I'm no expert, but I don't think there's much that is "technically" wrong with freeze 12. It was run in my truck for 7 years because the tech that serviced it didn't clarify to me at the time that it was different from R-12 (at the time, I thought it was a brand name). It's simply not commonly used in MVAC applications. Keep in mind that A/C shops already have to keep separate tanks for every type of refrigerant they service to avoid cross-contamination. They also either need separate gauge sets for each, or flush their hoses when switching refrigerants. Thus, a shop that sees a blended refrigerant is likely to turn it away entirely, or ONLY work on it if allowed to convert to pure R-12 or R-134a, which will require flushing. I'm talking about reputable shops of course, not ones that could care less about cross contamination.

This is all entirely separate from the argument that no motor vehicles ever came from the factory with Freeze 12 installed. Others have indicated that it's performance is no better than R-134a which is the primary component. Thus, you're left wondering "what's the point of using Freeze 12"? Unless you're absolutely convinced that it has a performance edge somehow, which has not been substantiated on this forum of folks who do it for a living and are likely to know, then I, too, fail to see the point in using it.

NickD on Wed July 17, 2013 3:53 PM

Should still follow all of the R-134a guidelines for a conversion, since Freeze 12 is primarily R-134a, in particular, the accumulator or receiver. If not R-134a compatible will dissolve the dyer and really destroy your system Its been so long since this Freeze 12 subject came up forgot the name of that other refrigerant, but it is a mixture, not a homogeneous refrigerant.

If either leaks out, one or the other will first, then you really will have major problems.

Are you lucky? Freeze 12 is the most powerful refrigerant in the world, did I fire five or six shots of this stuff.

webbch on Wed July 17, 2013 4:49 PM

The "Other" refigerant is HCFC-142b. Apparently, it's normally used for blowing polystyrene and polyethylene foam. Not sure if it's in the process of being phased out.

So Freeze 12 is 80% R-134a, and 20% HCFC-142b.

iceman2555 on Wed July 17, 2013 4:57 PM

Here is the link. www.technicalchemical.com/techsupport/techtip7.pdf?


Freeze 12 is a blended refrigerant...MSDS www.technicalchemical.com/msds/6030.pdf?

The blended refrigerant is a replacement for R12. The pressure/temp are almost identical to R12...slight variations, but very little different. The problem with FR12 is that this chemical is a blend and will fractionate within the system. One gas may leak more than the other, and the system should only be charged as a LIQUID to insure proper mix of the blends. Does it work....test have shown that it does perform, however, there are multiple drawbacks to using this chem. First and primary the chance to contaminate someone's rec/recharge equipment when the system is serviced and a refrigerant ID'er is not utilized. Serious problem. Must be recovered (legally) and can only be used once. Since it must be charged as a LIQUID, this prevents the average DIY"er from ever charging his vehicle properly. An undercharged system will produce performance issues....probably similar to this mentioned here.

Since the post mentioned that the condenser had been replaced....a suggestion would be 134a with a complete charge. Remember that the system should be charged by weight and not pressures...pressures are not an indication of a fully charged system.

Corvettes are notorious for having cabin cooling issues.....there is simply so much heat generated and then absorbed by the passenger compartment. Keep the heat out and the vehicle perform very nicely.

Several suggestions were made....spend the cash and time and the system should function.....cooling in Las Vegas in the summer....not too sure about that one....may take a bit longer for those vents to drop down...but this should occur. IF equipped with glass tops....locate the interior covers and block this extra sun load.

Heck, in Philadelphia this week....it is hot....very damn hot....driving a new 14 Impala and it takes time for this vehicle to cool down. An AC only transfers so much heat....reduce heat load....and the cooling temps are more acceptable.

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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

blfastvette on Wed July 17, 2013 10:44 PM

thanks for the extensive write up! the problem with using weight vs measure is the original system was modified when i swapped out the condensor and so was the required weight and volume. i am going to go to lengths if i have to to get it right, i once charged a 90's taurus at 70 degree ambient with 134 and i watched the vent temp drop to 37 degrees, so i intend to find the flaws in the system, there is more to it than just the fact the car is a hot box, like the orifice tube is a foot from the evaporator and the tube that the orifice tube itself is in is uncovered 12 inches long in an engine compartment of 150 degrees and then there is the hvac housing protruding into th 150 degree compartment with nothing but an 1/8 in fiberglass wall, also i have read and it makes sense that r12 would use a different size orifice tube over 134 as these are different gases with different size molecules, the bottom line is i drive the sh.... out of this car and i will be comfortable! i also need to work on the cfm out the vents as well, if need be i will go to the junk yard and check out the ford systems as the seem to get some pretty cool air out the vents for 134, i can only insulate the vette so much and dont really want to tint, so the journey continues

iceman2555 on Thu July 18, 2013 12:17 AM

The charge rate should be the same as R12. There is no need to short charge the system. A quick an test for proper charge is to simply measure the inlet and outlet temps of the evap after several minutes of operation. The temps should be the same.
There is no need to change the orifice tube....stay with the white GM unit...it will work as designed. Not so sure why so many DIY'er seem to believe that the system must be re engineered to function. There is so much erroneous information posted is so many sites that it truly baffles me. There are several functions that need to occur within the system to produce cool/cold air. Insure that these conditions are met and the system will function as designed. Attempting to make major modifications to the system often results in a non functional system.
The change of the condenser will benefit the OE R12 system by removing one of the stumbling blocks of the Vette system. Now you have a more efficient condenser and this unit should increase the temp drop/sub cooling of the refrigerant when using R12/FR12 or 134a. This alone should decrease evap inlet temps several degrees. Changing the orifice may actually contribute to a slight increase in liquid pressures due to the more restrictive orifice tube size.
The exposed low pressure liquid line (orifice tube) could be insulated with AC insulation tape, although the temp increase is probably negligible. But what the heck...insulate the darn thing...surely will not harm the system. Try insulating the accumulator also. GM has a foam type cover for the unit or use some insulated foil...this will also aid in a slight reduction of temperature contamination. Use the foam case or some type of insulated foil. Should be available from most commercial HVAC supply houses. Ford used a foil insulation on the evap case of many of their units at one time. Not too sure how effective this material was....they spent the money...so must have performed as designed. Have removed many of these things over the years...they simply fall apart....never had a come back due to failure to cool properly. But any insulation that can be done to the fire wall and foot wells will reduce cabin temps.
I think one of the best insulations would be the DynaMat (?) under the carpet and cover as much of the interior firewall as possible. Feeling a bit ambitious...pull the dash out and completely insulate the cabin fire wall. This alone should drop cabin temps significantly. Keep the heat contamination out of the cabin and enjoy the cooling. Running headers...wrap the headers....once more reduce the heat signature from the engine.
Make sure the fan clutch is fully operational. Vettes used the heavy duty fan clutch and often for cost reasons they were replaced with the standard duty units. The heavy dute unit engages earlier and produces less slippage than the standard unit...thus more fan speed.
Take your time...think thru your repair and make wise decisions....the AC system used on Vettes is the same system used with other GM products...and they cooled very well. The problem with Vettes is the lack on insulation within the cabin....high engine heat loads due to location and size of engine compartment. Also, check the air ducting for proper sealing. The age of the vehicle may result in loss of duct work sealing....the black stuff that blows thru the vents at times.....wrap the connections with AC tape (Home Depot) not the silver duct tape....use the foil tape...works better...easy to install and remove.
Seal it up...insulate the darn thing....insure proper engine cooling...charge the system...and you should be good for those hot nites in Vegas.
Good luck

-------------------------
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

blfastvette on Thu July 18, 2013 2:02 AM

thanks for the extensive write up again, i will defintitely look towards insulation, seems like my pressure is still a fair bit too high on the high side, not quite sure how i would measure evap inlet and outlet temp? with a laser thermo? i will definitley be doing some insulating, orifice tube, accumulator fire wall etc...i have the biggest parrell flow condensor i could get with a 2000 cfm fan right on it, insulation is a good idea as i am sure it gets to atleast 150 under the hood on a hot day

mk378 on Thu July 18, 2013 8:56 AM

Infrared thermometers aren't accurate enough for the evaporator inlet vs outlet test. Use two thermocouples or other contact methods. Someone once sold a kit with heat-indicating tape to apply to the pipes but I don't know if it exists any more.

wptski on Thu July 18, 2013 12:08 PM

blfastvette on Thu July 18, 2013 1:21 PM

what is the logic behind measuring evap inlet outlet temps and how realistic would this be for me to make happen $ wise?

mk378 on Thu July 18, 2013 10:40 PM

In a properly charged CCOT system, the evaporator fills up with liquid refrigerant that is in the process of evaporating. Thus the temperature throughout the evaporator is the same, or even slightly lower at the outlet (due to lower pressure there). If undercharged, the outlet pipe will warm up relative to the inlet.

blfastvette on Fri July 19, 2013 3:47 PM

the orifice tube in my car is 12 inches from the evaporator in the engine 150 engine compartment, seems in rather in efficent to me

blfastvette on Fri July 19, 2013 3:49 PM

could the orifice tube not be moved closer to the evap?

blfastvette on Fri July 19, 2013 3:52 PM

i understand the hot box that the vettes are especially in the sun but, side by side in the shade i think the ford systems are far superior, i charged one with 134 and watched the vent temp drop to 37 degrees, i dont think i could get 37 out of my vents on a snowy day!!!???

blfastvette on Fri July 19, 2013 3:55 PM

once i am done insulating the vette as well as possible should i go to the junk and reverse engineer the 90's ford system?? they blow damn cold even with the 134???

wptski on Fri July 19, 2013 7:05 PM

blfastvette on Fri July 19, 2013 9:20 PM

yes r-12 seems to be defintely more effective than freeze 12 or r 134