Getting ready to restore A/C operation after being without it for a couple of seasons. Not very knowledgeable on A/C...so I have a couple questions (end of this post).

History:
I'm 2nd owner (since 1999). A/C made it until 2010 before needing service.
2011 added 2 cans of R12. It took 4-5 years to leak out (below low pressure threshold).
2016 added 1 can of R12. It took 2-3 years to go below low pressure threshold).
2019 didn't run A/C that year.
2020 added 1 can of R12. Because clutch didn't engage, measured pressure...still below threshold.
2020 + 2 wks. Measure pressure again...which had dropped 10 psi. Tried to find R12 with dye.
2020 + 4 wks. Problems popped up with car starting. Laptop wouldn't connect...let the car sit.
2021 Replaced MAF relays and CTS. Car running fine again.
2021 Researched R12 vs. R134a vs R12a

Observations:
Many R134a sound happy. Some not as impressed. R12a owners also seem happy.
One post made lots of sense: Put Freon in the system it was designed for!
AFAIK...Slow leak points to failing seal (or shrader valve).
R134a molecules smaller (easier to leak) and not designed for older systems...tho it works "fine".
R12a is "flammable"...but so is R134a? (by-product of non-o-zone depleting properties)

Plan:
Refill with R12 (Found 2 cans -- in addition to 2 cans in hand). Also pressurized oil (4oz maybe?)
Because R12 with dye not available....Will replace all seals and dryer (shrader included).
Disconnect compressor, condenser, dryer, and evap. Lube and replace O-Rings. Reassemble.
Renting vacuum from AutoZone. Pull down vacuum. See if vacuum holds (gauges?).
Try to find R12 gauges (or buy them).
Fill with 2.5 cans of R12.

Questions:
How long to observe vacuum? Which port to measure that? Assume gauges show vacuum (neg pressure?)
Will I need to jump low pressure switch -- to engage clutch? If so, how? (Where is it?)
Is my plan flawed in some way? Should I be reconsidering R134a and/or R12a?
Should I add pressurized can of R12 oil? (Heard most of oil "sits low in system" and may still be in there after seal installation.
Assume I should add oil (which hasn't been delivered yet.) Any problem adding all of it? Can too much oil be in system?



Thanks!

 

There are several brands of R-12 Replacement gases. My neighbor tried some replacement Freon "R-12" substitute on Ebay and put it "in" his expensive Porsche system and ended up buying a new compressor two weeks later. Be careful out there, trust no-one when it comes to R-12 unless it is in the original Can. At big car shows there will always be at least one person selling the R-12 "Replacements" it seems.

I have been happy the R-134 and it's results have worked for me in my 1988 C4. I drained it out and then flushed the lines and added a new drier while at it and then I pulled a Vacuum and filled it up. R-134 is no longer the inexpensive gas any more. Harbor Freight has a nice 2 stage Vacuum Pump for less than $100 so I bought one. I have a good set of NAPA brand Gauges and the hoses mare clean and ready. I have since converted several other Cars for people as it is not that hard to do when you have the right tools.

Some folks claim you should install a new R-134 style Condenser before wrapping it up. My system was simple, it was just a matter of following the instructions that came with the first kit along with a new drier. The kit was less than $20 and the R134 I bought and had at home. I guess it really boils down to where you live, does it get HOT or just hot? Some people swear that the R-12 Freon was the best at making coldest air, we have seen thermometers showing ridiculously low temperatures using it. I do clean my radiator and Condenser using Coil Cleaner to ensure that they are corrosion free and able to transfer more heat.

I can live with the inexpensive kit (~$10 at Amazon) and though the temperatures in my C4 aren't "Ice Cold" it is still "cold enough" to have to throttle it back after a while. It is a whole lot better than the old Vent Windows folded back to force air into the Car. How did we ever live so long without Air Conditioning in our Cars?

I vacuum tested my system for 24 hours to be safe.

 

My particular manifold set only reads vacuum on the low side if I remember correctly. When I rebuilt my system I went to the parallel flow condenser (I suspected my leak was in my condenser but could never find it) and let it hold vacuum overnight. I also rotated the compressor a couple times during it just in case that seal was the source of the leak.

I converted to R134a for the relative ease of obtaining it, just in case a hose were to leak. I adjusted the switch on the low side for the cutout pressure, and then recharged by weight as best I could. (Being a different than stock condenser, I had to guess somewhat as the system volume changed plus I was using r134 instead of r12.) I also flushed the system and replaced the orifice tube and accumulator... on 90+ degree humid days I see 38-45 degrees from the vents. So as far as I'm concerned that's about as good as the system can operate. When stopped it warms up a little bit but that is most likely because of my under drive pulley setup spinning the compressor slower than it probably should be at idle.

 

I have an 86.
when i bought it, a/c no worky.
took it to an a/c shop. $300 labor, $600 compressor.
screw that.
so a friend said change the orifice, add 134 freon.
so i did, borrowed gauges, carged with 2 1/3 cans.
worked pretty good for about 10 years.
then a can a week to keep it cold,
someone else told me i should get “barrier hose”. The freon was leaching out through the hose.
i just went around and overtightened all the fittings, freon has been good since..
i had a leak i could not find. My friend who owns a corvette wrecking yard said its probably your compressor and they reseal them for around $65.
so i did and it has lasted pretty good, just adding freon every year.
Don’t know where the leak is, but i can do 3 cans of freon once a year till it gets worse.
then i will have to find it. Or sell it.

 

Maybe it would have helped if I said I have 2 cans of DuPont R-12 and can get 2 more of the same thing. AFAIK, that IS the genuine article. The same seller will provide a can of R12 oil and the lube necessary to do the seals.

If I can't get it to seal "air-tight"...meaning no need to refill for years, I'd probably be more inclined to opt for R-12a or 134a. As pointed out 134a isn't cheap anymore either. Knowing Dupont, they are probably about the release long-term studies saying it's bad AND they have the newest/best thing that everyone needs to go to. That's what they did with R-12, right?

Anyway, it SOUNDS like the R-12 replacements are about as "viable" as 134a any more? One other question I should have asked is if R12 "equivalents are compatible with R12? IOW, if I go thru with the R12, can I periodically fill (top-off) with R12 replacement...until it's basically converted via "leak-fill-leak-fill"? (If the seal kit doesn't fix the problem)

No one said how to by-pass the low-pressure switch on an 89....to force the clutch to kick in.

 

If you have it it makes sense to use it obviously. Mine was refilled with 134a way before I got the car so it was an easier choice for me.

Yea, 134a is out, as it's a greenhouse gas (we replaced an ozone depleting gas with a greenhouse one ironically). The new stuff is r1234yf... my truck runs it. The system is however pretty different from a traditional 134 or 12 system in that I doubt it would retrofit and work in any reasonable fashion... and a can was like 100$ last I checked.

For compatibility, I'm unsure as I've never used them however I would guess it should be as it's marketed as a substitute no? I glanced at red tek and it seems to suggest it is compatible as a top off.... however I am not certain. It seems to be propane based or similar hydrocarbons so I would guess it should be able to be mixed with residual r12...

As far as the low pressure switch, I have no clue... I'll assume it is different enough from my system and refrain saying anything as it's probably not the same and I wouldn't want damage to occur or say something that is incorrect... Sorry.

Edit: just re-read what you meant about the low pressure switch. No need to jump it. With the system under vacuum the first hit on the recharge will be enough of a hit that it'll come back on and run. At least it was on the few systems I've worked on.

 

R134a is $5 a can. Retrofit and relax. Before charging replace every Oring and seal. I would bet most are leaking. Pull a vacuum and watch for 12-24 hours, if it holds, charge it up.

 

For the sake of ending junk science brainwashing we have all been forced fed for decades... CFC's don't deplete Ozone, never reaches it and it's impossible to deplete the ozone.Ozone is created by the sun. Both dissipate and don't do anything.

 

I did the epa online exam, sent in my cert to these guys Frosty Freeze on ebay, and got my R12 products no problem. This link has the R12 with Dye R12, R-12 Refrigerant, 28 oz. Disposable Can, With RED Dye Charge, R12 | eBay It seems everyone has had good luck with purging the old lubricant in the system. Permeability could be an issue. I just opted to stay with the original but the conversion sounds interesting if you have the tools, but then again, my thinking was to avoid getting creative with pressure switches, and opening a system that other wise seems to run normally. R12 isn't like its radio active or anything, and its contained in a closed system. According to the epa guide, you do not even have to proof a R12 system for no leaks. I figure not being able to cool is probably a strong incentive to convert! charged up, my temp drop across the vent was about 60 degrees.

 

R12 was created in 3 days by GM in 1928, before we had "real science' about the environment. Like every other mess we humans make it takes a boat load of scientists and politicians to change complacency. I remember the ozone hole was a pretty big deal back then. Converting or 'evolving" refrigerants seems like a small inconvenience even if you want to call it that, to not "possibly" threaten the ozone layer. Now what the heck are we going to do about Global Warming? Now that is a minor inconvenience to figure out, LOL!

But to your point the article does say it is a Theory in 3 places .... speaking of R12.

EPA 609 guide.
"Depletion of Stratospheric Ozone In June 1974, Professor Sherwood Rowland and Dr. Mario Molina of the Department of Chemistry at the University of California at Irvine first proposed the theory that certain chlorine-containing compounds could pose a threat to the stratospheric ozone layer above the Earth. The Rowland-Molina theory states that CFCs would ultimately cause damage to the stratospheric ozone layer, which protects the Earth from harmful levels of ultraviolet radiation from the sun. What follows is a summary of the current theory held by the EPA. Refrigerants that contain chlorine but not hydrogen are so stable that they do not break down in the lower atmosphere even one hundred years or more after being released. These chemicals gradually float up to the stratosphere, where the chlorine or bromine react with ozone, causing it to change back to oxygen "

 

I'm completely aware of how ozone is formed. That being said, for the sake of not arguing about it, all I stated is what most people accept about the product. Should it reach it, the reaction is quite rapid for the given quantity of CFC present. I've done nearly the same workup lab scale so I know it happens, but I can't speak for if it reaches that layer or not.

I apologize if I ruffled feathers with that one, just what was hammered into me during undergrad. Reached a point it wasn't worth trying to discuss anything on the contrary with professors because they just didn't want to hear anything but how right they are about everything...

 

I don't think any feathers ruffled. Just decide if you have a leak or normal seepage and figure out if you need a tear down and/or a recharge. Some do conversions and feel great. Some do just keeping topping it off with R12 and feel great. Its a long term evolution to modern refrigerants. That's the only point. Its a 30 y.o car. eventually the A/C medium will be completely non-sequitur, non-relevant since the epa rules are fairly lenient and you can still get R12 legally.. not 12 A or B or C, Do what ever seems correct for you. In response to A/C restore title. There is R12 out there, plenty for now, you just gotta jump through hoops to get it. From my own experience if your juicing a can every year, there is a real leak and it wont be long until it's obvious and not patchable. Normal eventual wear and tear. EPA rules seem to say run it out, until... its time to repair, or upgrade. the market seems to say convert since 134 is cheap for now but if you don't have a (big) leak, then why convert until you are sure. If your charging every year, its time to take a close look. ?

 

I would totally agree with what's posted here. I am not looking for a fill once/year fix. When I reached that point, I'd either look further into what's causing the leak (and probably be forced into 134a or R12a) due to each of acquisition. Or, at the extreme avoid driving the car when temps are in the 90s. After all, they are [essentially] meant to be driven open cockpit.

And....It's not just that I wouldn't enjoy pumping refrigerant into the atmosphere. Who likes have money "seep" out of their wallet on top of that?

 

On the topic of oil... you don't see it visible anywhere correct? On mine it would coat around the compressor and edges of the condenser after a while on the solder... If not, I'd just add what the FSM reccomends for the drier replacement. If I remember correctly it's only a few ounces and you dump it right in. Now if you plan on doing a flush while apart I'd just add the full service quantity per the sticker under the hood and or the fsm... thats my take on it.

 

I converted my 89 over to 134A and am satisfied with the result.
Pulled the compressor, drained all the mineral based R12 oil out of it, replaced that amount with PAG 100.
Replaced the drier, added 2oz. of PAG oil before connecting the hoses.
Bought a can of AC system flush and flushed my condensor, evaporator and hoses to remove the residual mineral oil. Added PAG oil to the condensor and evaporator.
Replaced all the O rings with the green R134a compatible ones.
Purged the system with nitrogen 3x, pulled a vacuum of 29.5 inches for about an hour, system held that vacuum for 45 minutes so I was sure there were no significant leaks.
Charged with 2.5 (12oz) cans of R134a
Ice cubes yea!

EDIT-I have found the cheap aluminum conversion fittings in the box stores problematic and leaky. NAPA has a better quality kit that use steel valves FWIW.

 

Got side-tracked on my deck project....back to finish A/C recharge (prompted with this thread). One question I should have asked is about sensors/switches. Even if I swap all seals and pull a vacuum for a sufficiently long period of time -- hoping the charge holds for a period of years, what about switches/sensors?

R-12 is obviously expensive now (which I WAS planning on using to recharge my 1989). The downside is there may not be any facility (or other means?) to recover Freon if something else happens. Specifically, I've been thinking about a 30-yr-old electronics failure. My 89 is 32 years old now. The hoses look pretty good still so I'm hopeful of getting a seal. Now I've been thinking about the possibility of a high/low pressure switch failing. Would anyone recommend any other "maintenance" before re-charging the system?

As mentioned in my OP, I have new seals and a drier. Those will be installed prior to vacuuming. Are their any other areas (switches?) that might be prone to failure down the road?

FWIW, This other thought has me reconsidering 134a. Currently I have 4 cans of R12, acquired at $25/can. It takes 3 to fill the system -- leaving 1 to spare. It looks like the "going price" of R12 is $40/can on eBay now. Maybe I'd be better off selling and going with 134a despite any loss in cooling? If my odds of success are high -- for a multi-year repair, I'm still inclined to keep the system as designed.

 

Well all the switches are mounted on Schrader valves (at least on my 84) so if a high or low fails you just replace it. On an 84 there is a compressor mounted switch for the fan that actually mounts into the compressor case. If that failed I would need a full recharge. However I am unaware if later cars have a switch of sorts there as well.

Basically, short of a seal failure, you can replace electronics without losing charge it would seem. The Schrader my seep a little with the sensor off but while doing a quick part swap it is almost negligible. Unless you suspect it being an issue I wouldn't worry. They're relatively basic switches and fairly robust.

 

From my observations and experience, either R12 or 134A will work equally well in your Corvette if done properly. I recommend resealing any older compressor. Resealing a Denso is cheap and easy. Even a tiny leak not only releases refrigerant, it will prevent pulling a good enough vacuum to get every bit of air and moisture out of the system which is very very important. I also recommend replacing old hoses if you want to be leak free long term. I replaced my low pressure switch with an adjustable one because the pressure difference needed is not the same as with R12. I ran the vacuum pump for 45 minutes then let it set for an hour to make sure I had no leaks. I used a scale to measure my R134 charge. After pulling a vacuum the system pulled in the correct charge without even starting the motor so no need to jumper the low pressure switch. I started the car, 85 degree day parked under my carport and let it run with the temperature set at max cool. The air temperature at the center vent dropped to 23 degrees and the compressor was covered with ice. I adjusted the low pressure switch to cycle the compressor off at about 38 degrees so the evaporator wouldn't ice up. It works great now. It has been said that R134 conversions don't cool as well as they do with R12. I haven't found that to be true in a c4 corvette.

Another trick I learned on the early c4's is remove the center vents and dremel out the plastic that covers half of each vent on the inside. It gives you much more airflow.