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A/C R12 => R134a help

ssb on Thu October 22, 2009 11:32 AM User is offline

Year: 1974
Make: Chevy
Model: Corvette
Engine Size: 454
Refrigerant Type: R-12=>R134a
Country of Origin: United States

Needing some expert advise on installing a new ac system on my 74.
The car: coupe, 454 BB stroked to 489 ci. New DeWitt aluminum rad, dual fans, dual fan PCM control, new 74 evaporator, modified evaporator case to accept a later model, 1" longer fan; installed all new seals in the evaporator case; sealed all of the factory ductwork connections using 3M high density foam, insulated all of the floor and firewall with double aluminum sided jute under the factory insulation on the new carpet.

I am planning to use R134a and have been looking at the new Sanden 507 compressor, and also am looking to buy a new style horizontal condensor, not using the old snake style. Is the Sanden 507 the right selection? (have seen specs and I like!!!)

I have called a few new AC companies, and they tell me that unless I install ALL of their components, including their duct work and hangy down evaporator case, into the car, they will not warrant the cooling system . . . okay . . . and I'm in no mood to remove all the work I have accomplished thus far.

First: Should I or do I need to replace the existing VIR? I understand generally how it works, but since I am swapping over to R134 should I replace it? Why or why not. Anticipating taking it apart this weekend to make sure it is an original VIR, not EEVIR. (have owned her since 1978) and never taken it apart. What then should be replaced?

Second: If the VIR must go, what is the best system/combination of parts? One with an expansion valve/drier, or an orfice tube/accumulator? Types preferred? Is there any system other than VIR that does not cycle? Can the newer Sandens live without cycling or must they cycle? Cycling pros/cons?

Third: Has anyone out there been able to successfully keep the factory evaporator case and evaporator, 74 style, and upgrade from R12 to R134 and enjoy stellar performance?

Lastly: Please let me know if I have not asked the right question, and feel free to answer that question!
Southern gal needs to be COOL!!!

JACK ADAMS on Thu October 22, 2009 1:56 PM User is offline

If you do not have to convert to 134a, then stay with the R-12 refrigerant as these Corvettes did not cool that well to begin with. The VIR was not designed to work with 134a refrigerant, so they offer a VIR replacement that will convert to an Accumulator and CCOT. The kit comes with a pressure cycling switch and a few fittings that will need to be added to your system. One of your hoses (Suction) will need to be rebuilt with a new fitting (supplied in the kit) for this conversion. Are you still using the A6 compressor? Now if you are keeping the A6 compressor on the car, then stay with R-12 and rebuild the VIR. The A6 compressor was not the best compressor to operate with 134a refrigerant and for cycling.

Hope this helps and good luck.

ssb on Thu October 22, 2009 5:39 PM User is offline

Not only did they not cool well, they also had a tendancy to overheat in stop-go traffic when the a/c was turned on and bogged the engine down.
I am currently looking at the new style Sanden 507, maybe 508 compressors. They deliver better displacements, more pistons, higher rpm cooling capacity without the overheating problem and is said to deliver better cooling power at higher rpm speeds and less notability of engine bogging. I have a funny feeling that with the way air pollution control is going these days, it's not going to be long when R12 will be a thing of the past. I would also like to keep weight down to a min if possible. Also like the look of using the new Allen Grove brackets for the compressor since room is a big issue for me.
She has new Hooker headers with 4" side pipes and bung for air sensor.
Thank you for your reply and question.

JACK ADAMS on Thu October 22, 2009 6:21 PM User is offline

Well since you have your mind set forth on 134a then you will also need to use a Universal Parallel Flow Condenser or similar designed for 134a refrigerant.

bohica2xo on Thu October 22, 2009 7:00 PM User is offline

So much BS here, where to even begin?

Quote
Originally posted by: ssb
Not only did they not cool well, they also had a tendancy to overheat in stop-go traffic when the a/c was turned on and bogged the engine down.

That car did overheat. A big block shoved into the tight engine bay - loaded down with emissions controls that caused huge heat loads. A 454 can run an A/C compressor easily, if it can't produce 10 hp for a compressor it will not move a car very well either.

Quote
I am currently looking at the new style Sanden 507, maybe 508 compressors. They deliver better displacements, more pistons, higher rpm cooling capacity without the overheating problem and is said to deliver better cooling power at higher rpm speeds and less notability of engine bogging.

Huh? Are you just quoting the garbage some sales department sold you?

1) Better displacement? Really? That sanden is 7 cubes per rev. The OEM A6 is 12 cid. LESS displacemnt in the Sanden.

2) More pistons? Yeah, and smaller too. So what.

3) "Higher rpm cooling capacity"? Nope. Not anywhere on the output curve will 7 cid work out better than 12 cid. Besides, you state the issue is "Stop & go traffic" - which is low speed operation. Idle performance suffers with a reduced compressor capacity.

4) "Without the overheating problem". This is true - due to the 60% reduction in capacity at idle. Less heat removed from the passenger compartment, less heat in the condensor. The engine may run cooler - but you won't.

5) "Less bogging"? Sure, 60% reduction in load at idle. If it "bogs" you need to work on the carburetor...

Quote

I have a funny feeling that with the way air pollution control is going these days, it's not going to be long when R12 will be a thing of the past.


R12 will be around longer than the high octane gasoline that will support that engine. Speaking of pollution controls, are all of the OEM controls in place on your 489 cid stroker? Will it pass smog?

Quote

I would also like to keep weight down to a min if possible. Also like the look of using the new Allen Grove brackets for the compressor since room is a big issue for me.

She has new Hooker headers with 4" side pipes and bung for air sensor.

Thank you for your reply and question.

Ah, the old weight & size argument regarding the A6. It came OEM in the car, so we know it fits. If a few pounds are make or break, you don't need A/C anyway. All straw man arguments made to sell parts to corvette, camaro & chevelle owners.

Based on your original post, you have no aversion to modifying things for better performance. Neither do I. If you really want improved A/C performance, you need to move past the hype, and build a system to do what you want. Otherwise just add a parallel flow condensor, service the VIR & charge with R12. The VIR will not be happy with 134a.

If you want to discuss a high performance system upgrade, I will be happy to help.

B.


-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

ssb on Thu October 22, 2009 10:06 PM User is offline











Edited: Thu October 22, 2009 at 10:38 PM by ssb

ssb on Thu October 22, 2009 10:33 PM User is offline

Quote
Originally posted by: bohica2xo
So much BS here, where to even begin?

That car did overheat. A big block shoved into the tight engine bay - loaded down with emissions controls that caused huge heat loads. A 454 can run an A/C compressor easily, if it can't produce 10 hp for a compressor it will not move a car very well either.

Yes some of the following (above) information is put out by vendors, but the general consumer, me, has to do a good bit of research to ferret out the truths, half-truths, and BS. i have purchased all of the A/C books that i could find and have even obtained a text used in refrigeration classes used before r134a was an issue. by the way, if you can recommend any good books i am very interested. the problem has been that none discuss the specific issue of a conversion such as this.

and the straight talk on this forum is much appreciated!

Quote
I am currently looking at the new style Sanden 507, maybe 508 compressors. They deliver better displacements, more pistons, higher rpm cooling capacity without the overheating problem and is said to deliver better cooling power at higher rpm speeds and less notability of engine bogging.

car moves very well thanks! i agree that there should be no issue turning any of the compressors, but i am also considering that there is limited space in the corvette on the passenger side. so the smaller the compressor the better in that respect. if i have to get to something like the original A6, i can; or even the newer aluminum A6 (10 piston) type.

Quote
Huh? Are you just quoting the garbage some sales department sold you?

yea . . . that's why i need help from those who have to make these things work, not just sell them!

Quote
1) Better displacement? Really? That sanden is 7 cubes per rev. The OEM A6 is 12 cid. LESS displacemnt in the Sanden.

looks like i got that one wrong. the original 74 vette had a 10.8 ci A6 -- don't know why they didn't use the 12 ci?. if i understand correctly, this has a direct relationship with the amount of heat capacity the system has so i do not want to reduce that value, i need it to be increased. what is the correlation of displacement to heat duty when converting from R12 to R134a?

Quote
2) More pistons? Yeah, and smaller too. So what.
okay, not really relevant for this BB . . . but drag is worth looking at, i.e., for ways to compensate if value is large

Quote
R12 will be around longer than the high octane gasoline that will support that engine. Speaking of pollution controls, are all of the OEM controls in place on your 489 cid stroker? Will it pass smog?

well the engine has about 10:1 SCR and a happy DCR as well as AL heads to help with today's gasoline -- i think the static CR could actually be a point higher and i'd be okay. i do not live in a state that requires inspections, but i'm sure i pollute less with this combination than the original car did from the factory, gas mileage is the same, A/F ratio is correct, car is driven a fraction of what it was when new; this is a whole 'nother forum! But i was referring to the political climate with regards to refrigerants in general. i know that R22 is going the way of R410A now, and have no idea what is to replace R134a which i read will be sooner than later.

Quote
I would also like to keep weight down to a min if possible. Also like the look of using the new Allen Grove brackets for the compressor since room is a big issue for me.

Quote
Ah, the old weight & size argument regarding the A6. It came OEM in the car, so we know it fits. If a few pounds are make or break, you don't need A/C anyway. All straw man arguments made to sell parts to corvette, camaro & chevelle owners.

weight is not a make or break issue but is just one part of a technical evaluation and it probably will carry much less weight than other components (no pun intended). i actually do not have factory brackets for the A6 and the rear factory bracket would not work with headers, and if you know big blocks, i.e., many belt options, i will be running a different v-groove from factory.

Quote
Based on your original post, you have no aversion to modifying things for better performance. Neither do I. If you really want improved A/C performance, you need to move past the hype, and build a system to do what you want. Otherwise just add a parallel flow condensor, service the VIR & charge with R12. The VIR will not be happy with 134a.

If you want to discuss a high performance system upgrade, I will be happy to help.

thank you for addressing these questions -- i am very interested in a discussion of a high performance system upgrade for this car. the only thing really keeping me from just installing whatever is the best "replace everything" kits is that i think about everything from the firewall back is already in very good shape or brand new. as a note, the 74 evaporator has two main refrigerant lines and one small liquid line that i don't know what to do with without the original VIR. the thing is that if i have to even replace the evaporator, i may as well pull the engine as there is only about 1/4" from the evap housing to the valve cover. then i know that i will get the "while i am at it" disease and ty to install a 6 speed auto . . . etc., etc.

Thanks for reading and your input!
also, thanks for the link to the condensers!

ssb.

Probedude on Thu October 22, 2009 11:37 PM User is offline

Quote
Originally posted by: JACK ADAMS
Well since you have your mind set forth on 134a then you will also need to use a Universal Parallel Flow Condenser or similar designed for 134a refrigerant.

How do you mount those condensers? Looks like the upper and lower rails are only attached to the fins and not to anything else substantial. What happens with vibration or when the fins start to thin and rot? Are the rails sufficiently strong?

Dave

bohica2xo on Fri October 23, 2009 2:43 AM User is offline

SSB:

Glad to help. You are right the OEM compressor was a 10 cid A6, but most of those got replaced with 12's someplace along the way - at least in my experience.

You are on the right track with planning a large PF condensor. Make sure it is well coupled to the radiator fan assembly, so that all of the air the fans move passes through the condensor.

Your evaporator has an oil bleed line, just like earlier models with a seperate POA valve. The bleed line allows oil from the evaporator to return to the compressor even when the POA has reduced suction line flow. The bleed line can be capped if you are not using the VIR...

You should consider mounting a V7 compressor on this vehicle. This may require some mount scrounging, or modification. If you are considering a change to a serpentine belt system this is also possible. What you get is this:

The V7 is a variable displacement compressor that is designed for 134a. It incorporates evaporator pressure control, which provides the same function as the POA valve. The suction pressure is controlled by de-stroking the pump, which reduces power consumption. It is the right displacment 10.9 cid (179 cc) when it needs to be, and can de-stroke to 10cc / rev when it needs to. The V7 is used in several GM platforms, including later Corvettes. V7 Compressor It is available as an ear mount like in that link, as well as a cross bolt mount. While pictured there with a serpentine drive, a V belt drive is available for the V7 as well.

Some custom plumbing will be necessary of course. A TXV will need to be fitted to the evaporator in place of the VIR. A suction line will be needed to fit between the evaporator discharge & compressor suction. The VIR is removed. A conventional high side receiver dryer is needed, bit it can be located anyplace between the condensor discharge and the TXV - it does not need to be where the VIR is now.

I am a big fan of the V7. They will take 6500 rpm all day long, and have plenty of displacement. They are designed for 134a, and several control valves are available. With a conversion like this you get to keep TXV / POA performance, full displacement - and gain variable displacement economy. Should be able to do it without yanking the big iron out of the bay too.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Edited: Fri October 23, 2009 at 2:45 AM by bohica2xo

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