dprantl

I bet it would make anyone jump! If I saw high-sides going close to 400psi, I would start to run away.

Anyway to the original poster, whichever way you decide to go, that self-recharge kit you posted a link to is a very bad idea.

Dan
'91 928GT S/C 475hp/460lb.ft

Dan87951

Just bring it in and have the put evacuate and the system to make sure there is no leaks and than have them charge it. To be honest after buying the cans recharge cans at wal-mart to have a professional do it is not much more. That last evacuate and recharge cost me about $50 if I remember right. To cans of freon will almost cost you that much..

Randy V

My suggestion is just go to Pep Boys, buy a recharge hose with guage and get a can of R134. Straight R134. Don't use the stuff that contains leak stop.

Less than 30 bucks.

Then follow the instructions and add the freon to the low side port.

Done.

rgs944

If you know a good shop guy that is a good way to go Dan. The problem is that most shops have a lot of money into there equipment and they want to get at least $250 out of every AC customer that comes through the door. Lets just call it gravy for a lot of shops, especially when the temps rise in early summer. To be fair there is another reason shops charge so much for AC work. They do not want to be responsible. Charging an old system might work only for a short while. Then the customer is mad at the shop for screwing up there AC unit. Overall I think it is best to just learn a little about the AC system and do it yourself.

dprantl

Going out and just buying a recharge can is a really bad idea. A system that has been empty of refrigerant for too long eventually gets air in it along with some water vapor in the air. When you connect that charge kit and charge the system, all that air and water in the system is going to wreak havoc. On an empty system, IMO it is a requirement to at least use a good vacuum pump to remove all the air and boil off the water in the system. I would change the receiver-drier as well.

Dan
'91 928GT S/C 475hp/460lb.ft

nuc

Lots of good posts here since I left last night.



I posted those #'s merely as an example of the pressures being +/-10% of each other.

Actual press./temp. chart is here

http://www.peachparts.com/shopforum/...9&d=1145327904

As you can see, 12 and 134a are around +/-10% at all temps.

If their popping in Georgia (high pressure valve pops ~525-550 psi), then there's no way cars would be able to be driving in Florida, Nevada, Arizona, Death Valley, etc... and be blowing cubes. Like I said before, numbers approaching 500psi and there is something wrong with/in, the system.

Take a look at the pressure chart, to approach 500psi with 134a, in a correctly functioning a/c, you would have to have ambient temps. close to 150 deg. F. Now it does get hot in Georgia, but not that hot

Now, back on topic, enough with the minutia.

Rastapapa, another option is the DIY/928 way. Instead of spending the $ at a shop, spend it on a good two stage pump and a set of gauges. Don't worry about a micron gauge or nitrogen.

You can now do all the a/c repairs you want, in the comfort of your own garage. And, especially if you ask lots of questions, you'll KNOW its been done right.

WallyP

OK, here is a better plan.
1) Buy a paperback manual on charging auto A/C systems. Read it. Twice.
2) Go to your local Autozone or equivalent parts store and check into their tool rental/tool loan program. My local Autozone will sell/rent/loan (they have used all three terms) an R-134a manifold gauge set for $99, and a vacuum pump for $199. Buy the R-134a there (if you are a nice guy) or at Walmart (if you are cheap).
3) Check the non-running system pressure. If it is at least 30 psig, you are golden. If it is zero, you have a problem. In either case, pump the system down, close the gauge valves and see how long it takes for the vacuum to leak away. If it is minutes, find the leak and fix it. If it is hours, charge the system to about 80% of the system spec for R-12.
3) Return the gauge set and vacuum pump and get your money (all of it) back. This is not a scam, it is the way the tool loan program works. I assume that they will also have some sort of leak detector in the system as well. They will NOT have the tools in stock, but can have them there the next day in most cases.

blown 87

Yea, they have 134a in systems with out the safeties that turn the compressors off at high pressures like the factory 134A systems do.

And they do pop off the safety valves according to others that I have talked to that are in this line of work.
Not a problem as long as the car is moving, but let it sit and idle for half an hour, things change.

rgs944

Those sound like some very good tips, I have about three cars I need to address the AC system in this spring so I will look into that.

blown 87

ALL ways wear safety glasses when working on AC units.

SteveG

3 cars = keep the gauge set. One of the reasons the shops want to evac a system is so they can charge the system by weight (ozs). That way they know there no "mixture" in there and they know exactly how much to put in, no overchargeing, which is as troublesome as low pressure. (Robinair's charging station isn't a scale but it shows liquid ozs. -- too complicated to go into here) Anyway, for the DIYer, it helps to know pressures, rather than just dumping a can into the system.

The sticker is prob gone on your car which would tell you, but IIRC a 928 w/o rear air is 28 ozs, 33 with. I forgot you were converted so ignor the ozs, you need to know pressures. The numbers, above are for R12.

rgs944

I have converted the 968 but I think I am leaning towards buying R12 for the 928. I am a little confused on what is needed for R12. It sounds like you need different gauges for each? I would assume autozone would not carry anything for R12 specific.

SteveG

Uhhh, you can't mix/switch manifold hoses back and forth or you will contaminate both systems. Plus the fittings are different in order to prevent this from happening. This is what makes a shop shun r12. If you mention r12 they will chase you off the property, b/c they are afraid there is some unknown concoction in the system and it costs $$$$ if their equipment gets contaminated.

Correct about any chain store and r12. You can prob only find products on ebay from indep suppliers.

Better to pick same refrigerant for all of your cars. This is part of what I was saying about using the term Freon interchangably. If you mix systems, it is truly a bucket of worms.
Some people will say in going to 134a from r12 that you don't need to change gaskets (O-rings). There are some oils that can go either way and some that can't.

Pick one or the other. Get 6' (hose) gauge for the particular system. Search here for info on A/C or buy a book.

dr bob

A legal 'conversion' will have a label that tells what oil is used. POE oil is OK to go back to R-12. PAG not such a good idea. Else flush and change the oil. You'll want to see what the pressure in the system is now. If none, plan on finding the leaks and buying a new drier at minimum before you put anything in the system.

Proper fan operation is mandatory for converted cars, barely not quite so mandatory for R-12 cars. AC won't do well at all if the fans aren't in top condition.

------

There's more than a casual amount of science to AC systems in the cars. The instant top-off charging kit from JCW is intended for a system that still has plenty of refrigerant in it, so you are adding more gas to a partially-charged system. An empty system is a whole different story. Leaving any significant air in the system, for instance, dooms you to warm air temps, like 50-60º best. A little moisture thanks to a saturated drier means possible icing in the expansion valve, possible compressor problems with the dead-headed system. A system that's leaked refrigerant has also leaked out some of the oil. How much? You can guess and worry, or you can flush the system properly and put the correct amount back in.


and FWIW, you can buy that same charging kit and the cans of R-134a in the automotive section at your local Wal-Mart.

blown 87

I cant tell you how many AC systems I have "Fixed" by flushing the oil out and charging with the proper amounts of freon and oil.
My guess is that 95% of the time when oil is added to a system with out a full and complete flush, and that means taking most of the system apart and off the car, they end up way over full on oil, and this hurts AC performance.
The newer systems are going to be charge critical, some of the articles I have read they are talking about 2 QZ or less of freon in newer systems.
These are going to be a mess when they start to have issues, there will be no more lets just throw some freon in it and see what happens.

Glad I will probably not still be working on cars when this filters down to shops like mine.

I agree about air in the systems, we vacuum down the gauges and all the hoses as a unit when doing a full service, you do not want air in them.
We also change the oil in the big vacuum pump every time it is used.
once the oil gets moisture in it then it is not capable of getting moisture out of any oil that is left in the system.

I have a 5 CFM deep vacuum pump that I like to leave on for at least 24 hours to get any moisture out.

I do not have a thermistor vacuum gauge that most here seem to think you have to have to service AC units, nor do I know any professional that does own or use one.

I plan to buy one so I can say I have it, not sure if i will use it or not.

Doing AC work for money is a high dollar thing, multiple charging machines, flush units, dye injectors, multiple, big vacuum pumps, multiple gauge sets, identifiers, etc, all of that equipment cost money, and for the most part you need it to do a good job on many cars.

Then some idiot comes in who has tried to fix it himself and put sealer in one and it stops up a recovery machine, that will get this hillbilly fired up.