R-12 to R-134a conversion


Old 09-02-02, 07:11 PM
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Unhappy R-12 to R-134a conversion

After reading as many threads as I could find on changing over to R-134a, I realize now that I did EVERYTHING wrong! I have a 1989 Mercury Sable LS with a 3.0L engine and automatic transmission with overdrive. The A/C system has an FS10 compressor. I would like to repeat (out loud with someone else listening) what I think is the correct proceedure for the change over, and have you point out where I've still gotten it wrong. I will have to dismantle and back flush the system, including the condenser, evaporator and lines. The accumulator has to be replaced. The compressor has to be removed and the oil drained from it and measured. (Does the compressor need flushing or can it even be flushed?) Before reassembling the system replace all O-rings with new ones and lubricate them with the new refridgerant oil. Fill the compressor with new oil, the same amount that was measured when it was drained earlier. (Can you fill the compressor with too much oil?) Now, reassemble the system and evacuate. Check to see if system holds the vacuum, and if it does not, then I have a major leak. If no major leaks are apparent, then I should pull the system down for at least 30 minutes. I have a venturi type vacuum pump and air compressor,
which pulled the system down to about 29 inches of Mercury. Do I need to evacuate longer than 30 minutes? Ok, here is where I am really lost. Should I have put the new refridgerant oil into all of the system's other components (condenser, evaporator, accumulator) before I reassembled the system as I did with the compressor? Or, should I put in a can of oil charge after I have evacuated the system and just before I start to charge the system with R-134a? And speaking of oil, which should I use, the PEG or the Ester? I have noticed that the PEG comes in different viscosities. Which (viscosity) should I use if I choose that oil? Finally (I hope), my manual says that when charging with the new refridgerant, the engine should be started and the A/C switch left in the off position. The R-134a (can) should be inverted when charging, then after the first can has pressurized the system, then the A/C switch is turned on so that any other cans are drawn into the system by suction. I thought I read in this forum that you should keep the can upright when charging. Which is it, inverted or upright? And it is the pressures (high & low) that determine proper charge, not the number of pounds or ounces of refridgerant put in. Does any of this sound close to being right? Please point out any misstakes and add anything you think might be helpful. No item is too small to point out. Except for the A/C, my Sable is in mint condition and I just had it painted last year, and I want to keep it for as long as I can. Thanks in advance.
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Old 09-02-02, 07:29 PM
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1) Pitch all the O rings, replacing them with newer compatible ones.
2) Flush the ENTIRE system throughly with a flush gun. Autozone might carry them or rent you one.
3) The FS10 compressor is complete junk and chances are at this age, it's wiped or will wipe out on you when it's all said and done. I believe a new compressor is on the bill for this repair.
4) New barrier type hoses
5) New receiver dryer.
6) THOROUGHLY inspect the system for any damage.

As you can see, this will get quite costly. Be careful. A 1989 Sable is NOT the bastion of quality and has a very poor transmission. It would really stink to put 500+ bucks in an A/C system and have the tranny puke out on you. Sad, but true. Many a running Sable or Taurus to the yard with a bad tranny. The yards are littered with them .

You might choose to get some literature from Four Seasons or the library on the charging of AC systems so you do it right. Do yo have R134A gauges as well?
Old 09-03-02, 08:14 AM
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Unhappy R-12 to R-134a conversion

Thanks for the information Joe. Even though some of it was really bad news, I will take it to heart. Yes, I have the R-134a guages and my flush bottle and gun should be in by Friday. I'll try to find the other information you were talking about (Four Seasons), and I'll go over my Haynes A/C Manual again to see if I overlooked anything. My transmission has not given any trouble in almost 150,000 miles, but I change the fluid and filter every 50,000 miles. It's due for a change now. Hope I can get at least another 50,000 miles out of it. If I don't, then I will not worry about it. I'll just try to fine the money to replace the car. Mainly, I like trying to keep it going myself,and the things that I learn while doing it! Thanks again for all the help!
Old 09-03-02, 09:46 AM
Dan Meyer
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Let me add some things. Don't flush the compressor, expansion valve, orifice tube or accumulator or drier. Flush the compressor with the PAG (not PEG) oil after you have drained and measured what came out. You can drain it pretty good by turning the clutch.
Refill with the same amount that you originally took out. Add about one ounce of oil to the condensor and evaporator.Use the same viscosity oil as was originally in the car. 30 minutes is NOT long enough to vacuum, even with a piston type vacuum pump. With a venturi it might take a couple of hours. If the hoses are in good shape, they need not be replaced. R-134a does not need barrier type. Add a can of the R-134a UPRIGHT (GAS) with the engine off - can be added to both the high and low side. Then add the rest ONLY to the LOW side with the engine at approx 1500 - 2000 rpm. It only takes about 70% of R-134a to equal the original amount of R-12. USE GAUGES AND PRESSURE NOT AMOUNT OF r-134A. I wrap a heating pad around the can to speed up the refilling. Good luck
Old 09-03-02, 10:33 AM
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Assuming it has not lost any oil since 1989. Not likely .

Get the required amount of R134A oil capacity from the parts vendor or Ford and go from there.

Also you will be pitching the dryer in favor of a new one as the R12 dryer is likely bad and seldom is the old one compatible with R134A.

Replace the hoses for good measure. They are in a gazorch of a location and likely porous and rotten being from 1989. Do the job once, do it right. You'll need to take the hoses off to inspect and replace the O-rings anyhow.

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