75 a/c upgrade

**Pat Bush** · June 29, 2003, 03:25 PM

Re: 75 a/c upgrade

Ralph -

I have some experience dealing with VIR based cars. The fellow I had working with me was a commercial and residential air conditioning professional. You can take this for what it is worth but here is what he told me when I had the lock, stock and barrel discombobulated from my 73:

1) 134a will never blow as cold as R12. It has to do with the properties of the freon and the design of the system. Plus, 134a has higher head end pressures and the system components were not really designed for retrofit in 1975. It will work, but it is helpful to know what you are getting yourself into.

2) We had a devil of a time using R-12 just with a replacement compressor (had to "feel" the charge until it was right) simply because Corvettes have a different compression ratio A-6 than just about any other car and replacements are of the "many" rather than the "few". Those on the board believed I was stretching the POA portion of the VIR assembly to its limits given the higher compression ration of the compressor on the suction side. Yours should be an R-4 I think so or was that in 76? Perhaps this will not be an issue for you. I cannot even begin to figure what would happen with a 134a conversion....

3) You should probably replace your manifold and liquid lines if you were not planning to do so -- 134a has a different set of properties according to those I talked to and uses different rubber lines than R-12. Something about porosity not being a factor with R-12, whereas it is more of a problem using old lines with 134a. Again, having battled with my 73 system to restore back to original R-12, you just don't want to go there again!

4) Before you install, soak all the o-rings in the oil you use to charge the system. The AC guy was emphatic about this and I still am not sure why but I think it has to so with the seal and longevity of the seals.

As for your questions:

1. Will I have to break down any of the hard plumbing between the POV/VIR
and the evaporator to change o'rings?

Yes. There are seals at every hard junction point between components. You will need to remove the VIR valve and change the dessicant bag at a minimum if it has not been done. Plus it ain't a bad idea to purge all the mineral oil from the valve. I need to tell you the VIR valve on my 73 was hard as #$% to remove/install and is right up there with the lower radiator hose in terms of patience and difficulty. However, the green 134a O-rings will work fine with R-12 too if you ever decide to go back. VIR valves are "all in one" units and what I was told were they always had some sticking problems here and there usually on the POA side. A great idea that never quite made it to complete design success....

2. What components should I have flushed, if any?

If you have already broken the system open, I would do as much as you can. 134a uses a different oil altogether, plus, there is always moisture in the system. On mine, since all the components were essentially new, we didn't flush but charged with nitrogen first to pressurize the system and remove moisture, then test for leaks, and then we charged. The nitrogen thing is a great thing to do in any event even if you flushed the system.

3. Is it necessary to replace POV/VIR to upgrade to r134.

I do not think so, but I would definately change the dessicant bag, and see if there is a POA insert designed for 134a pressure changes. These do exist for pre-72 conversions. I don't think they exist but perhaps someone else has been there and done that. I know there are kits to convert your VIR assembly to a orifice type found on later 70's cars but I haven't tried or used them on mine. It works!

In closing, you may want to consider using either the real McCoy (R-12) or one of the blends (Freeze12 etc...) instead of changing over (several guys have done this with good results for drivers) -- if you are converting to 134a, your charge fittings will be different anyways and I assume you just want it to work like most of us. The idea is to get it as comfortable as possible in the compartment -- and I know how much time and effort it takes to get this done. I just don't want to go back there again! The design of your system is for R-12 and if you change over you will take a deduct at NCRS judging for a 134a conversion I would think. If you have done a good job on everything else, it oughta last for a long time since it is essentially a sealed system.

Hope this helps -

Regards -

Pat Bush

**Ralph Spencer** · June 29, 2003, 06:29 PM

Re: 75 a/c upgrade

Pat, Thanks for your response, and a fine one it was.

I am going to leave it r12, probably cost a fortune to fill but like you said,
it is a sealed system and with a good installation, I shouldn't have to fill it again.
I will have the components flushed, replace o'rings, and dessicant bag.
New box gasket kit and see what I got.
Thanks again for the good info

Ralph Spencer

**Randy S.** · June 29, 2003, 08:19 PM

Re: 75 a/c upgrade

Ralph,
I am at the same point on my 66. A couple of issues I have run into:

After reassembling the rebuilt components of the system ,I cannot seem to maintain a vacuum, the first step in charging your system. In order to find the leak(s) you have to pressurize the system and use a dye. If you choose R12 it will be costly to chase down the leaks. Once R12 is in the system it cannot be recovered. My AC shop is advising to charge with r134a to chase down the leaks. r134a CAN be recovered and reused, Once I have a sealed and reliable system and if I am not happy with R134a after a few months, I can always get a home equity loan and go back to R12.

Re oil. R12 uses mineral oil and R134 uses PAG oil. They are recommending Estercool, a synthetic oil that is compatible with both.

Check the archives, lots of experiences out there.

**Ralph Spencer** · June 29, 2003, 09:24 PM

Re: 75 a/c upgrade

Couldn't you as Pat suggested, fill it with nitrogen and die to check for leaks as opposed to using r134 then use r12. I just seen 30lb of r12 on ebay for $475.
By the way does anyone have an idea of how much I will need????

Thanks again all
Ralph Spencer

**Pat Bush** · June 30, 2003, 04:26 AM

Re: 75 a/c upgrade

Randy -

I read your post. I had no problems whatsoever using 12. It's been in my 70 and 73 coupes for over 2+ years. Still blows ice cold. Does your car have crimped hoses or barbed fittings with refrigerant line and clamps? I seem to recall the older ones being done that way.

The test procedure I mentioned to Ralph goes as follows -- it has always worked for me:

1) Inspect all threads, fittings, and components for wear and/or corrosion. Key areas for leaks are the front seal on the compressor, all fittings, schrader valves, or your hoses. Usually the evaporator is OK. Condensers seem prone to leaks not because of design but location of unit and fittings.

2) Soak all the seals in the refrigerant oil of your choice (mineral for R12, PAG for 134a). Install and tighten to spec. I always hand start all the threads, look for any crossed threads, and make sure everything is clean where I am working (as well as my hands).

3) Pressurize system with Nitrogen. Nitrogen is a lot cheaper than R-12 and it does a great job of removing moisture from the system. We pressurized to around 180 psi with gauges and then monitored the gauges on the system for 24-48 hours. If you have no pressure drop, you are cool. If not, you will have to start checking each fitting and component front to back using a leak detector until you find the offensive bugger. We didn't use a dye -- the fluid we used was a biodegradable, thick, bluish stuff -- don't recall the name. It made BIG bubbles when there was a leak. Repeat this step until it holds pressure.

4) Now de-pressurize the system and evacuate it. We pulled mine down to around 300 -- and it held.

5) Now charge. I understand your trepidation with using R-12 as it is expensive. But if you do the nitrogen thing, you will never use a drop of R-12 until the system is already in a sealed, pressure tested, and evacuated state.

Many auto AC shops do not use nitrogen to pressure-test but I understand it is a common practice in commercial HVAC circles.

Hope this helps -

Pat

**Pat Bush** · June 30, 2003, 04:30 AM

Re: 75 a/c upgrade

Ralph -

Look on the label on your compressor (most times). It will list the correct charge there or on the evaporator case label (some times). Any competent service manual will also tell you the correct charge amount. My A-6 system took 3.25 lbs to charge. Usually runs between 3 and 3.5 lbs. You should be good with 6 cans (so you have a little extra for the future or just in case :-)

Pat

**Jim T.** · July 2, 2003, 09:36 AM

Re: 75 a/c upgrade

Ralph in converting to R134 your R12 system requires only a fill of 80-85% of the original amount because of the expansion properities of R134.
Here is a web site that has some useful information on the conversion.
Interdynamics at www.ID-USA.com. Good luck let us know what you do and how it comes out.

75 a/c upgrade

75 a/c upgrade

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