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Author Topic: A/C Conversion R-12a to R-134a  (Read 245 times)

Offline weitrhino

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A/C Conversion R-12a to R-134a
« on: 04:31:17 PM / 12-Jun-18 »
I'm in the process of doing an open system R12 to R134a conversion. Because I'm feeling my way through the process I thought I'd post here and open up the project to discussion.



When I bought the car about 4.5 years ago the PO had said the A/C system was dealer-added, not factory. It didn’t work and I didn’t mess with it but that’s what I learned after bringing it up at the time of purchase.

The refrigerant obviously had leaked out so this seemed like a good opportunity to fully convert. I ordered a new receiver/drier and an O-ring kit and began to disassemble all the pipes and hoses using my ’85 FSM for reference. One of the first things I noticed is the high and low pressure valves are not up by the firewall as indicated in the manual. One was down near the compressor and the other up near MAF and had a 90 degree port adapter. Something was weird about that but I couldn’t put my finger on it….yet. The damn auto parts stores don’t carry any such conversion adapters so I’m waiting on one to be delivered but in the meantime I could continue with the O-ring replacements and clean up the compressor which was pretty gunked up on the outside. It was a big PIA to get the cooling unit out from under the dash but I wanted to clean it out and replace the O-rings at the expansion valve. It had a bunch of leaves and crap built up inside that I blew out. In for a penny…..



It’s a 33 year old Nissan so there have to be a few hiccups but I was pretty shocked to find I couldn’t pour much if any compressor oil out of the MJS170 compressor. The manual says there should be 150ml in the system. Oil apparently gets carried throughout the system with the refrigerant so it seemed logical that a lot of it also leaked out. The various pipes and hoses were drained before reassembly. Removing the compressor wasn’t too bad, two bolts underneath, two more on top and loosening the tensioner from below.

I found a pipe joint near the battery and another near the condenser fan that don’t exist in the manual and chalked it up to this being a dealer installed system. These aluminum pipes are insulated and this is what happened when I tried to take one connection apart.



Well shit! And to make matters worse I couldn’t find anyone willing to repair or duplicate this piece of hard line. Every A/C specialist shop simply said “no” until I reached an old guy in Tulsa who had been in the business over 35 years and had a much broader skillset. I sent the twisted pipe and seized connector to him and got it back looking nearly new about 10 days later.



This insulated line runs the width of the engine bay between the radiator and condenser. The insulation was dry rotted so I stripped all the tubes exposing oxidation hiding within. A little work with a kitchen scratch pad shined them up again then I insulated them with new closed-cell foam. Steel tie wraps secure the new foam because I didn’t want to worry about plastic tie wraps breaking down under the high heat between the radiator and condenser. Here’s what the new insulator looks like installed.



With all the O-rings replaced and the piping fully reinstalled it was time to add oil to the compressor. I went with Ester oil because it’s supposed to be fine if it mixes with any of the old oil still in the system.



So in goes the oil but it seemed to be going in rather slowly. I could turn the compressor by hand and it burped out a bunch of air but I had some trouble getting all the oil into he system. Air continued to burp out when I turned the compressor but when it wasn’t, the oil level in the big syringe I was using would rise back up. Logic suggested turning the compressor would draw the oil into the system, so what gives? I took a closer look at the MJS170 compressor and discovered that’s not what I have! I have the A5000 compressor which technically belongs in an ’84, not my ’85! Although they look identical the high and low pressure hose attachments are reversed and the A5000 system is supposed to hold 270ml of oil, not 150ml like the MJS170. The only thing I could think to do was to turn the compressor backwards and try to get as much of the oil as possible into the low side. For now everything is all sealed up while I wait for my 90 degree adapter.
« Last Edit: 06:20:34 PM / 12-Jun-18 by weitrhino »

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Offline weitrhino

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Re: A/C Conversion R-12a to R-134a
« Reply #1 on: 06:28:59 PM / 15-Jun-18 »
It's been 96 to 102 degrees (F) :evillaugh: here in north Texas and that's just too damn hot to have a non-working A/C system.   

My 90 degree high pressure R134a valve came in a couple days ago and yesterday I got to work on it. After a trip to the local Auto Zone and I was back with their loner vacuum pump and a manifold gauge set. After I had everything connected I powered on the pump which was missing one foot, leaked oil, and had a sight window as clear as black coffee. The FSM says to run the pump about 20 minutes so I stepped back inside for lunch.

Twenty minutes later I see the low pressure gauge is parked at 10 Hg and will go no further. At my altitude I should get approximately 28 Hg so this was a head scratcher. I shut off the valves and disconnected the gauge set and the low pressure side zipped to 10 psi with nothing connected, so obviously this gauge is crap. I had vacuum in the system but had no way of telling how much. That's all the time I could afford so this morning I went back to Auto Zone to return both the leaky vacuum pump and the crappy gauge set.

I had bagged the pump but it rolled over in the trunk and leaked oil all over my carpet.  :glare:  There's no stain but I know it will attract dirt over time and I get the lovely smell of Pag oil every time I open the trunk. Of course Auto Zone doesn't have another gauge or pump to loan so off to O'Reilly's down the street. Their pump disappeared last year and they never bothered to replace it, but they had a gauge set and their store on the other side of town had both. Better to get both at the same location, says I. Yay, a trip across town. For those who are counting this is the third trip to a second parts store for this job.

Maybe O'Reilly's is on their game after all. At the across town store they have a pump that's still in the box. It's used, but just barely. Win! At first the guy tried to give me vacuum pressure gauge. "No, I'm not doing a leak down test. I need a manifold gauge set for the A/C system." They guy seemed a bit lost and asked a second guy who produced a manifold gauge set in a case that looks in pretty darn decent shape. Another win! So I plonked down my $300 deposit for both and headed home. Once I was back I set up the whole system again and started up the vacuum pump and had my breakfast while waiting. Twenty minutes later the low pressure gauge reads exactly 0.

Gawd!  :glaresad: Do I have a leak? Did I miss something? Did I leave something loose somewhere? Could it be the only part I didn't closely examine, the condenser which is made of hen's teeth, has some kind of issue? I pulled the hose off the vacuum pump and stuck my finger on the end. Yes, it sucked. (that's a good thing) I played with the valves but nothing changed. Finally I put the vacuum pump directly on the low pressure gauge and it stayed rock solid at 0. This makes the second gauge set that was complete crap. Yipee! I get to go back across town to O'Reilly's and of course they don't have another set. Advance Auto Parts is across the street and they have none, nor have they ever had them for loan. That was the 5th time I set foot in a parts store for this job.

Ah, but remember the first O'Reilly's had a gauge set so back across town I go. The guy I dealt with earlier is gone now and the three parts jockeys working there now insist no gauge set exists. Now I'm getting pissed off at the 6th trip into a parts store for this job to be told something completely contradictory from what I was told earlier in the day. This is the first time I've ever fooled with an A/C system so I'm already questioning every step I take. I don't need another curve ball to screw me up.

I have one option left; another Auto Zone on the far north side of town so I called them from the front counter in O'Reilly's. They have 2 gauge sets available. By the time I get up there and back home again I've spent 7 hours screwing around with this today, but their gauge set works!

Pretty darn close to 28 Hg



Vacuum is holding steady. In goes about 2.5 cans of R134a. Glorious cold air is finally mine!  :cool2:
« Last Edit: 06:41:37 PM / 15-Jun-18 by weitrhino »

Offline BOSSMAN

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Re: A/C Conversion R-12a to R-134a
« Reply #2 on: 12:57:31 AM / 16-Jun-18 »
At least you can still borrow tools from part stores.  Up here in the Great White North the biggest auto parts store chain (and the only one that I know) stopped their tool lending service a few years back so now I either have to rent or buy specialize tools.
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Offline taktics702

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Re: A/C Conversion R-12a to R-134a
« Reply #3 on: 06:43:53 AM / 16-Jun-18 »
Awesome! Keep us updated on your A/C adventures.  Let me know how it goes for you.  Ive pretty much replaced every AC part but not completely satisfied yet.

I live in las vegas so I understand the heat.  I am on an A/C adventure myself.  Got my AC to work pretty well actually but once it gets to above 100 degrees the performance dramatically decreases. Its like when its 90 degrees and below the ac blows ice cold. But once it gets to 100 and up the ac gets overwhelmed and struggles to keep up with the heat.

Im going to install a parallel flow condenser because it works better for r134a.  Get a custom hose made to adapt to the old piping. And then add a  12" spal pusher fan since my car doesnt have any auxilary fan. 

I will update you the results.

Offline weitrhino

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Re: A/C Conversion R-12a to R-134a
« Reply #4 on: 08:38:51 AM / 16-Jun-18 »
I don’t know where you could fit a second condenser so it would get enough air flow to efficiently shed heat but you could supplement with additional fans. There might be room enough to squeeze a second fan in there if you can find a way to mount it. If you do, I’d give it a low temp thermal switch or hard wire it to run when the compressor is powered. All that said I’m still not convinced any of that will help you get consistently cold air, even at 100 degrees. A second condenser means you’ll need even more R134a.

R134a is said to be less efficient than R12a and yet somewhat strangely when converting you're supposed to use about 90% as much as you would R12a. One thing I am convinced is necessary is to put the system under vacuum before adding the R134a. That’s much of what draws the gas into the system aided by the high pressure in the can. I suspect you have some air trapped inside that limits cooling efficiency and that’s got to come out. Vacuum is the only way to do it.

My process:

Expose every connection point and replace the O-rings
Remove and clean the compressor
Remove and clean out the cooling unit (and consequently the blower)
Strip all the dry rotted pipe insulation and replace
Replace the receiver/drier
Replace the service ports with R134a adapters (for mine, a 90 degree adapter was needed for the high pressure side)
Replace old compressor oil with Ester oil
Vacuum the system
Inject R134a
Sit back and say, “ahhhh”



Post Merge
At least you can still borrow tools from part stores.  Up here in the Great White North the biggest auto parts store chain (and the only one that I know) stopped their tool lending service a few years back so now I either have to rent or buy specialize tools.

That kinda sucks. I was frustrated to the point of nearly buying a $100 gauge set but held back because I still had enough doubt about my understanding of the process. I had been pretty convinced I had correct reason to distrust the gauge sets I had borrowed, but having two of them turn out to be crap kept me wondering if I was doing something wrong. I’d have been really pissed if i’d Have dropped the coin on a gauge set only to learn I was screwing up on my own.

Perhaps a trip south is in your future.
« Last Edit: 09:10:34 AM / 16-Jun-18 by weitrhino »

Offline taktics702

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Re: A/C Conversion R-12a to R-134a
« Reply #5 on: 05:04:35 AM / 19-Jun-18 »
No im replacing our serpentene design condenser with a parallel flow. Never had and aux fan since i owned the car so I will be adding a spal 12 inch pusher offset to one side. 

its a better design for r134a.  You should really look into it since you are basically overhauling your whole ac system.  Its one of our systems weakest links.  Ill show you with pics as soon as I can.

110 degree weather coming soon lol

Offline weitrhino

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Re: A/C Conversion R-12a to R-134a
« Reply #6 on: 09:36:08 AM / 19-Jun-18 »
At first I thought you were installing another condenser in parallel to the original. I understand now.

At any rate, I'm complete with my system and quite happy with its performance especially considering the A/C had not worked since I bought the car about 4 years ago. I don't know what the new condenser will cost you but I overhauled my system for cheap.

$27 for 3 cans of R134a
$7 for a refrigerant tap valve
$4 for insulating foam
$8 for steel tie wraps
$9 for a 150 piece O-ring kit
$? for one bottle of Ester oil (it was pretty cheap)
$6 for a 90 degree high pressure side R134 adapter
$10 for R134 adapter kit (only used the low side)
__________
$80 approximately

I did pay $56 to get that twisted aluminum hard line repaired, that was the biggest expense and turned out to be worth it. So, that's less than $150 for a complete system overhaul and conversion. I call that a win. Labor at a shop would likely have pushed the job over $1000.





« Last Edit: 09:41:26 AM / 19-Jun-18 by weitrhino »