# Converting A/c over to 134a! HELP!!!



## tookey71 (Aug 17, 2007)

I'm planning on converting my a/c unit over to 134a. Does anyone have any experince with this on nissan hardbody trucks(1991)? Would you replace expansion valve,evaporator tube and dryer? After draining oil and replacing compressor with pag oil ,any chance of compressor failing due to the mixture of the two oils? Anyones advice welcome . Thanks


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## Oldnissanguy (Jan 6, 2005)

I don't know much about this, but what I do know is that you need to flush out all the old oil and sediment or your compressor will probably fail. The oils do not mix well.


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## Nissanpickup (Nov 16, 2005)

well ur gonna need a r134a compressor and i have one other than that u can just pick up a cheap o-ring kit from discount and replace ur o-ring along with ur charge ports but if u want the compressor hit me up my dad put r134a on my truck but i dont want ac so i pulled the entier ac system out of it and now im tryin to get rid of the parts pm me ok


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## Copper93 (Mar 24, 2007)

I've converted several vehicles from R12 to R134a, the compressors are the same. R134a was formulated to work with the old systems. However, R12 and R134a do not mix well. You'll have to pull a vacuum on the old system. Pull a vacuum and let it run awhile. The vacuum wil pull out the old oil and R12, also the vacuum will boil off any water in the system. Any water in the system will cause corrosion in the system which is bad. 
R134a does not cool as well as the R12, you might want to add a electric fan to the condensor to help. As long as your moving you won't know the difference. You'll feel the real difference if you get in traffic.

Good luck, its not that hard just getting the vacuum is the hard part.


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## tookey71 (Aug 17, 2007)

Is there any type of A/C flush that would help with getting the old oil out of the system?


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## TXhwyXE (Dec 20, 2006)

Glad I ran into this thread. I also have a 91 pu 4cyl and need to convert to R134a. 
First let me mention that Autozone has a DVD to borrow for free that explains how to service an auto AC. I copied the DVD at home for my personal recollection because it was helpful. 

The compressor on my truck started leaking and lost all of my freon. I purchased an R134a compatable compressor for my truck off eBay. I just need to drain the mineral oil out and put in the right oil. 
If you are using the old compressor, it might be best to remove it and drain all of the R12 oil out then blow it out with compress air. 
Buy a can of AC flush. Orielly has it for like $10. I also purchased an AC oring kit from Orielly. You might as well do it right. Take your AC lines off, pour in a bit of the flush and blow it out with the air. Would not hurt to do it two or three times. Also do the flush out on the compressor. 
You will need to flush the serpentine condensor also. Best to remove it possible. Not that difficult. Just carefully remove the plastic front grille and unbolt a support center brace in front of the condensor. 
You can then tilt the condensor on a table to pour in some flush and then blow it out. I would do it twice. 

Please replace the dryer with one made for r134a. It is worth it. You could very well blow up the bag inside the old one when charging the system with the 134a. 134a takes more pressure to work than the r12 did. A blown bag will contaminate your whole system with the dryer descciant and you will have to start all over to flush out the crap. Also there is no way to remove all of the r12 oil out of the old dryer. 
I prefer a dryer with a sight glass if I can find one.

Someone knowlegable about ACs told me not to worry about so much about leaving r12 oil residue inside. He said the r134a freon today is more tolerate of it. 
He also said about the pressure, for r134a that the low side takes a bit higher than the specs like 20 lbs more. Can anyone confirm this?

The amount of oil to use should be on a label under your hood. 
But can someone please tell me if I pour all of that oil into the compressor or do I need to put some into the system as I charge it?

------------------------------------------
91 Nissan D21 pu 4cyl
97 Nissan XE pu 4cyl


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## Copper93 (Mar 24, 2007)

I've always been told to charge to about 80% of the R12 rating. R134 is a bigger molecule to stop the leaks common with R12. If you get a recharge/conversion kit from the parts store, it should have the ratings and charge specs.


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## smj999smj (Jan 1, 2006)

You can use the original compressor, expansion valve, evapaporator and condensor...although, a bigger condensor will make the system more efficient. The receiver/drier tank must be replaced; it's not so much that the R-134a will cause it to "blow-up," as will the desicant bag will gradually erode away with the R-134a and eventually leak tiny bits of carbon (or desicant) into your system. You should drain the compressor of it's oil and add a similar amount of PAG oil, but I've seen plenty of people not drain it and their systems worked perfectly fine. Add 2 oz. of PAG into the new drier and if you do flush out the condensor and/or evaporator, add 2 oz. of PAG into each of them, as applies. You only need to replace the "O" seals on connections that you open, as well as any that are currently leaking, obviously. Esther oil will work instead of PAG, as well.

The 80% charge rule is general and a good place to start, however best results are obtained by monitoring the high and low pressures and comparing to the service manual AC performance test. The low side pressure will probably not vary that much from the R-12's spec., as you are not replacing the expansion valve in the system. It's differant on GM conversions where the original orifice tube is typically replaced with the Ford, blue type, orifice tube, which will affect the low side pressure about 20 PSI. I've found in some vehicles that 80% charge is fine, but in some cases, had to add until I got to a 95% charge to get the system to work efficiently and the pressures to be in an acceptable range. Here's where how to read a set of AC gauges can make a big differance in the outcome of the job.


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