monkeyboy

My compresser just went out, so I am going to make the move from r12 to r134 while I in there anyway. I have ordered a rebuilt '89 compressor, a new dryer, and a system flushing fluid. Is there anything else I need. Has anyone else been through this? I called a Nissan dealer, and he said I need to replace the high and low pressure lines as well. Is that just an expensive alternative to flushing the system?

I have read that r134 is not as efficient, and needs a lot more pressure. Does that mean I should get a newer compressor (from a '93 or '94)? Would that be the reason for replacing the lines?

Lastely, I have seem some mentions of alternatives to r134, that are more efficient. Does anyone have any info on any of these?

Thanks!

John van de Pol

Going to R-134, even though it appears as an only path, is probably one of the worst things you can do. You are right in observing it's less efficient, pressures are much higher (350-400 psi as opposed to 200-250 psi on the high side). The molecules of R-134a are smaller so they can literally pass through the rubber of the R-12 AC hoses. The hose replacement suggestion should have added that you need to replace the hoses with BARRIER hoses. Besides replacing the drier you should replace all the o-rings in the system. The chemicals in r-134a and the compatible PAG oil are not compatile with most old r-12 seal materials.

There are great alternatives to R-12, One is a group called hydrocarbon refrigerants. They work great, but they are subject to a lot of hype, most of it against it (fueled by refrigerant companies whose interests are directly affected), but some of the supporters also overclaim abilities from time to time. Take some time and read up on it. There is a great and helpful board at http://www.aircondition.com/wwwboard/alternative/ There are some local legal issues to consider, but when reading through the counter hype, keep in mind that other areas in the world (Europe, Canada, Australia) are moving to these products big time because they are cheap, efficient, but to them, more importantly, they are completely environment friendly. R-134 is NOT.

An other group is made of refrigerant blends. They stay in the family of refigerants, without or with lower ozone depleting characteristics. The blend is mixed so that the temperature curves match that of R-12.

If you decide HC refrigerants or blend alternatives are not for you, there are two things to keep in mind when rebuilding ANY AC system running ANY refrigerant. Your system needs to be clean, and it needs to be dry. This is why you must flush your system thoroughly, there is no substitute. I would advise you, once you tear into it this far, to take out your evaporator and replace the expansion valve, this will allow for thorough cleaning of that major component and eliminates a current or future trouble that will be involved to fix.

Then, if you go with R-134a, consider the following. Moisture will chemically combine with elements of that refrigerant. This forms a caustic acid which will slowly eat away at all metal parts of your system from the inside. When the weakest one fails, you rebuild again (now this will take 2-4 years, no failure in mere weeks or months). PAG oil sucks up moisture like a sponge. It is horrible stuff. Moisture in an AC system should be to the tune of tens of parts per million. A brand new METAL can (very well sealed) of PAG will already have hundreds of parts per million. Left open for even a short period will yield thousands of ppm. A plastic container of the stuff will start at thousands of ppm. You can't vacuum the system dry because after a prolonged deep vacuum, the pag oil will boil off before the moisture does.

So look into using a new product: Poly-alpha oil it is compatible with both mineral oil (R-12) and R-134 systems and eliminates many of the downsides of PAG. It will allow you to create a properly dry system with the proper tools, without too much of a fuss.

Read up on this and make an informed decision that will work for you. Whichever way you go, best of luck.

John

davecmu

I don't know much about what you just said, John, but it sounded like the most intelligent and thought out thing that has been said on this board in weeks. Congratulations on being a major AC brainiac - or at least being able to convince people you are.

dat_nomad

That was so much usfull info I am more confused then when I started!!!! ( I was planning on doing this myself) Can someone plese translate what the hell all that meant? My mere college education cannot decipher the vast knowledge the was just spewed before me.

John van de Pol

AC Brainiac? Thank you, but I don't think so. I used to have a 92 Accord. After 8 years the dual pressure switch broke and allowed all the R-12 to escape. A dual pressure switch senses the freon line for too high of a pressure (which can lead to a catastrophic failure) or too low of a pressure (which can damage the compressor as it is starved of lubrication if there is not enough freon to circulate the oil with). The switch will switch off the compressor of the pressure is not within normal parameters. Oh well, things break after 8 years, so I did not think much of it and had it fixed. The R-12 that used to cost a buck a pound, cost me 42 dollars a pound that time (the system took 2.2 lbs). Then 15 month later the same switch blew again! I was told it was a weak design, even in a Honda. The freon by that time was over 50 bucks a pound. At that time I had also developed a very slow leak. Some repairman malpractise caused me to lose all my freaon for a third time, and that's where I drew the line.

I started researching for R-12 alternatives, and quickly found out about the various refrigerants I described in my earlier post. I became enamored with the HC variety by its promised efficiency improvements, which I realized in the Honda. I since converted my Max' R134a as well and dropped the pressures from 425 psi to 225 psi. Think of the horse power that saves. In my Max I initially had poor results, as the unit was not functioning properly prior to conversion with the R-134 either. I (mis)-diagnosed it as a stuck or malfunctioning expansion valve, but it turned out to be a partially blocked high pressure line. Liking to do things "right", I took the opportunity to superclean the inside of the system, replace the dryer and the expansion valve, and get all the PAG out (including the compressor) My system since then has been colder than the day I got the car (at 9k miles) and I have never looked back.

However, the knowledge I have garnered, I obtained by extensively reading the AC boards and any other source on HC I could find. I had spent time earlier in life figuring out how A/C works, so a lot of it made immediate sense, and it helped me segregate valid information from hype.

Hydrocarbon refrigerant is basically a mixture of propane and butane, and yes, it is flammable. But so is the oil in R-12 under pressure and the PAG oil / R-134 combination in systems. So reading up on the subject this was a big one to evaluate. I decided to go with it.

From the boards I learned how to fix a system right (clean and dry for one), and how to properly charge it with HC. HC really work poorly if you overcharge them so it takes some attention to do it right. In my post above I merely passed on some of the things I learned, and pointed people to the source of the knowledge as it is fairly difficult to condense months of reading into one or two posts.

Read and learn (this really applies to anything you try to figure out how to fix). AC has specialized knowledge, but there are no real secrets.

Good luck.
John