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Old 05-09-2003, 07:45 PM   #1
Scooby Guru
Member#: 4800
Join Date: Mar 2001
Chapter/Region: TXIC
Location: Houston, Tx
1990 Legacy & OB XT

Default Legacy A/C conversion - R12 to R134a Tutorial

Well I just finished up the conversion on my 1990 Legacy today to R134a. I must say, the conversion wasn't that hard and the results are good. I know people bitch and moan that converting doesn't work and blah blah blah. If you do it right, it works fine. Procedure should be similar if not same for imprezas too.

I'm goin to give a little tutorial on the basics of what needs to be done to have a successful swap.

The first thing that needs to be done is the system discharged. You can do this the "proper" way by using a vacuum pump, or just loosen one of the bolts a little and let things vent......you shouldn't do this....but I can't stop you

Next you need to get all the old oil out of the system. Most of it will be in the compressor and receiver/dryer. You will need to replace the receiver/dryer anyway, so you can leave that alone right now.

Unfortunately to get the oil out of the A/C compressor, you will need to take it out. Loosen the belts for the alternator & a/c, remove the lines from the compressor, and unbolt the compressor. Once you get it out, dump out the oil from the intake & discharge holes. Turn the compressor clutch a couple times to get any excess oil out. There is also a drain hole on the side of the compressor. It wouldn't be a bad idea to remove that and make sure everything's completely out.

Leave the compressor out for the time being.

Next remove the lines that connect to the receiver dryer, and also remove the pressure sensor. Once you have them disconnected, loosen the bolt that holds the clamp down on the receiver/dryer.

Check all the o-rings and make sure they're good. If they're good, you don't need to replace them. Mine were fine.

Next take some compressed air and blow through the line that goes to the condensor from the compressor. Put a rag under that line at the receiver/dryer to catch any oil or other gunk that comes out.

If you get any nasty black goo, or anything that looks bad, you should probably flush the system with some flush stuff.

At this point, you have the option to take the evaporator box out. You don't need to take it out, however gunk, leaves, etc gather in there and can cause things to stink up pretty bad. Mine was nasty.

Here's some pics of before an after.

Needless to say I took my evap box out. It really wasn't that difficult. You must first remove the lines that connect to the lines in the evap box. Once you do that you will need to take out the glove box, and the plate that it bolts to. There is a bolt at the bottom and nut at the top of the evap box. Remove those two and the whole thing comes right out.

I cleaned everything up with pinesol. It worked very well.

Once you get it clean, put it back in, in reverse order.

Now you're ready to put everything back together.

As I mentioned, you will need a new receiver/dryer. Just get the one for your car at a local autoparts store. I got mine at autozone for 45 bucks.

I guess now is as good as any to talk about other supplies.

Oil. r134a & r12 refrigerants use different oils. The oil acts as a means of transportation for the refrigerant. R12 systems use mineral oil. Most newer 134a systems use PAG oil. PAG oil is a synthetic oil. It however has zero compatibility with mineral oil. So it's not the best choice when doing a conversion.

Esther oil however does work with r134a, and is compatible with mineral oil. So you don't have to get every last drop of mineral oil out. However you should try to get as much as you can out.

So, while you're at the parts store, you will need a receiver/dryer, some esther oil, and some r134a refrigerant.

Note, you probably don't want to get the refrigerant that has oil and other crap in it. As it will probably have incompatible oil in it.

Now let's talk about the amount of oil & r134a you will need.

It will vary for different vehicles, but on mine, it said to put in about 5 oz. of oil. When you put the oil in, you want to put about 1 oz in the receiver dryer, and then put the rest in the suction port on the compressor.

For refrigerant. You want to fill the system to about 75-80% of the original r12 capacity. Mine called for about 1.8-2.0 lbs of R12, so I used 1.5 lbs of R134a.

Last thing you will need is the new R134a fittings.

So....now that you have all your supplies....time to put everything back together.

Like I mentioned, put about 1 oz of the esther oil in the receiver/dryer, and put the lines and the pressure sensor in it. The receiver/dryer should come with new o-rings....you can put those on.

Pour the remaining esther oil that your system calls for in the compressor, like mentioned above. Now the compressor is ready to bolt back in the car. Bolt it back in and connect the high and low pressure side lines. Put all your belts and such back together.

Now put on the new fittings, and you should be ready to pull a vacuum. I took my car to a shop at this point, since I couldn't find a place to rent a vacuum pump and it cost more to buy one then to just take it to a shop.

The hooked the vacuum pump up, sucked all the air out. This also boils all the water out of the system. Once it was all out. They let it sit for 10 min to make sure there was no leaks. He added as much refrigerant as he could with the car off, and then had me start it, and finished adding the appropriate amount of 134a.

That's it. It really wasn't that hard, and she blows nice and cold air. Only issue I have is that since I have an underdrive pulley on, the compressor really isn't spinning fast enough at idle speed. If I get ambitious I may swap it out for a non-underdriven, but lightened pulley. We'll see.

Total cost: $118.97 + tax

Receiver/dryer: $43.99
2 cans of r134a: $12.00
Esther Oil: $6.99
Fittings: $5.99
Labor for vacuum: $50.00

I got a deal on labor for the vacuum and charge....that may be a little more, depending on the shop you go to.

Not bad for $120.00, and it won't cost an arm and leg to recharge.

Also, forgot to mention I had the aid of a buddy who told me most of what I just told you. Plus he recommended the Haynes Heating & Air conditioning tech book. I think it was like $15. It has all the oil amounts & refrige amounts too.

Very helpful, and would highly recommend you get one if you are planning on do a/c work yourself

Here's the link to the haynes tech manuals

Here's the book number and info

10425 - Automotive Heating & Air Conditioning, Covers theory and operation of all heating and air conditioning systems in use today. Step-by-step procedures are provided for diagnosis, maintenance and repair.
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Last edited by Legacy777; 08-09-2005 at 11:41 PM.
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Old 08-23-2014, 05:41 PM   #2
Scooby Newbie
Member#: 285012
Join Date: Jun 2011
Chapter/Region: South East
Location: K-town, TN
93 Impreza L


I just did this to my 93 Impreza L. I simply ordered a new (reman) compressor and evaporator/dryer for a 96 with the same engine. Just swapped out those components, added the 134 adapters and had it pulled back down, and the 134 pumped in. Really easy.
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