A/C R12 to R134a Conversion Success

[Cruzerman]

I thought I would post a quick article on the retrofit of the A/C on the '93 FZJ80 from R12 to R134a. I bought the truck with a non-functioning A/C system. I have never worked on A/C and new little about how it worked, but after reading some posts here and other places, I thought I would tackle it.

My system was funky with a quick connect on the low side and Schrader valve on the hige. I assume the previous owner put on a quick connect converted on the low pressure side so they could squirt in one of those A/C fix cans. I assumed that the system was R12 and converted wrong, so went about doing what I believe is the right way. I was lucky in that the system was empty, so I didn't have to take it in to be evacuated.

The oil used in R12 and R134a are different and not compatible. So the steps involved are cleaning out the old oil, replacing all the O-rings, replacing the dryer, replacing the expansion valve, and converting the high and low side connectors from Schrader to quick connect valves.

I bought a manifold set and A/C system flush kit off Amazon, along with some A/C flush solvent. I also bought a new dryer, expansion valve, and O-ring kit from Rock Auto.

The hardest part was removing the evaporator so it could be cleaned out and the expansion valve replaced. Fortunately, there is a great write up on this by alia76:

https://forum.ih8mud.com/threads/a-...oling-unit-evaporator-expansion-valve.296748/

Other than that, I just cleaned out all the lines, condenser, and evaporator using the flush gun and solvent. It can get a little messy. I removed the compressor and cleaned it out as well. Put everything back together using new O-rings and the other new parts, along with 7 oz or so of PAG oil. I then pulled a vacuum using a Harbor Freight vacuum thing (I happened to already have this) for an hour. I let it sit for two hours and it didn't appear to leak, so I put in R134a.

My only issue was that my high pressure never showed what it should be. I put the new gauge set on another vehicle and it showed 200+ lbs. on the high side, so the gauge worked. However, I believe that the quick connect adapter I used on the high side didn't push the valve stem in all the way. That is all I can figure because it now works great and the air coming out the vents is in the 30's. The entire job cost about $175, with most of that being for the tools and A/C flush solvent.

 

[Timpanogos Slim]

I have seen people argue that the expansion valve does not actually need to be replaced, but that argument was made in part in reference to a system for which the only replacement valve available is known to be horribly unreliable

 

[ihatecrashing]

I'm getting ready to tackle the same thing. I'm debating on the oil change. I have read the oils are incompatible, but then I was told (probably unreliable source) that the oil for 134 is a different viscosity than mineral oil for R12 and could cause issues for the stock compressor. Did you feel like there was much difference between the consistency of the oils?

 

[Landseer]

The compressors are identical for a both the R-12 and R-134a trucks.

 

[Brunorelli]

So I've been researching this all summer. you can add r134 to the system if it still has r12 in it. There is enough oil in the r12 to keep lubricated for up to 5 seasons of refilling it at which time the compressor should seize from lack of oil. Adding the r134 actually increases the performance. It's almost to cold. You can buy the conversion fittings at wal mart now. I wish I would have done it a long time ago.

 

[DieselDriver]

I have done many different vehicles over the years! I have never done any more than add the 134a and have cold A/C!! The last one I did was my 91 LC, ice cold till I blew the motor, and then had it evacuated with a full charge, before that was my vette about 8 yrs ago same charge, still ice cold, zero compressor problems!

 

[Rifleman]

Sure, you can do all the steps the OP did, or you can just add the 134A and run it. We did many change overs in the shop, for the most part the customers weren't willing to spend the money to change the expansion valve and flush all the old oil, then recharge the system. The most important thing to do when doing this change over, if you system is empty (no pressure in the system) is to pull a vacuum on the system before charging it, to remove ALL the air and moisture. Then letting it sit for at least 30 Min. under vacuum to make sure you have no leaks, if you have no leaks then charge the system and enjoy the cool.

 

[Cruzerman]

For me, the system leaked out all it's contents and someone had already screwed with it. I had no idea what was done, what oil was in the system, etc. Since I was already going to swap out the O-rings, I might as well flush out the system. Yes, it was extra work and I had to buy a flush kit and some solvent. But it now works like a champ. Could I have just replaced the rings and squirted in some R134a? Beats me. I'm no expert. But I am pleased with what I did.

As for changing out the expansion valve. I was taking out the evaporator anyhow to clean it. The expansion valve was less than $15. No way I wasn't going to change it while I had it out.

 

[Funner]

I have done many different vehicles over the years! I have never done any more than add the 134a and have cold A/C!! The last one I did was my 91 LC, ice cold till I blew the motor, and then had it evacuated with a full charge, before that was my vette about 8 yrs ago same charge, still ice cold, zero compressor problems!

I did the same thing to 3-4 vehicles over the years. Just screwed on the adapter and filled the old system with 134. Never had a negative experience doing this.

 

[Landseer]

Sure, you can do all the steps the OP did, or you can just add the 134A and run it.

The problem with this is that mineral oil and R-134a are not miscible. In a normal system the oil and refrigerant mix and the oil is carried through the system maintaining lubrication for the compressor. If you fill an R-12 system with R-134a the mineral oil and R-134a do not mix and the oil will end up sitting at a low point somewhere in the system (probably the dryer in an 80), and the compressor will be starved of oil.

Many people have had success converting to R-134a by simply adding 134a and leaving the mineral oil in place. However doing so will eventually end up damaging your compressor. How long the compressor will last is the big question and will vary by application.

Another option would be to leave the mineral oil in the system and add PAG oil along with R-134a, the PAG oil and R-134a would circulate and the mineral oil would just sit at a low point somewhere.

http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/1193931/Re:_Why_are_R134a_and_mineral_

 

[Rifleman]

Another option would be to leave the mineral oil in the system and add PAG oil along with R-134a, the PAG oil and R-134a would circulate and the mineral oil would just sit at a low point somewhere.

Having to much oil in a AC system, be it mineral oil, pag, or both, can cause poor cooling, high pressures, or a failure of the compressor from trying to compress liquid oil.

 

[Cruzerman]

If you fill an R-12 system with R-134a the mineral oil and R-134a do not mix and the oil will end up sitting at a low point somewhere in the system (probably the dryer in an 80), and the compressor will be starved of oil.

Maybe this is why it is working for those that have tried it. On my R-12 system, the dryer is not the lowest point. It is mounted up by the battery. The compressor may be the lowest point, meaning that it gets oiled.

 

[Landseer]

Having to much oil in a AC system, be it mineral oil, pag, or both, can cause poor cooling, high pressures, or a failure of the compressor from trying to compress liquid oil.

This is absolutely true, although I'm not sure how much extra oil you would need to cause problems. Interestingly, adding PAG to mineral oil is the Toyota procedure for retrofitting to R-134a:
http://tms.cleanautoalliance.org/documents/ac002t98.pdf

 

[Landseer]

Maybe this is why it is working for those that have tried it. On my R-12 system, the dryer is not the lowest point. It is mounted up by the battery. The compressor may be the lowest point, meaning that it gets oiled.

I was thinking of the dryer as a local low point, the bottom of the dryer is ~6 inches below the exit and it would be a good point for the mineral oil to settle. I assumed that mineral oil was more dense than liquid R-134a and thats incorrect. The density of liquid R-134a is about 1.15 g/cc mineral oil is about 0.8 g/cc so the mineral oil would float on top of the R-134a. The only place I can think of that the mineral oil could accumulate would be at the top of the condenser.

 

[FZJ80 in KC]

Glad it all got figured out!

Sometimes people forget (or don't know) to remove the Schrader valve from the r12 port before screwing on the R134 retrofit fitting on top of it, so wonder if that gave you some of your issues.

Sounds like you got it figured out though, so congrats!

 

[BILT4ME]

Congratulations on getting it done and doing a write-up for others to work with!

 

[Mitch Jacob]

The compressors are identical for a both the R-12 and R-134a trucks.

If anyone's paying attention this thread, can you verify the R12 and R134a compressors are functionally equivalent? Meaning, any compressor can run either R12 or R134a? I have a 92 truck (3VZ-E) and replaced the engine with a 95 3VZ-E. The compressors are not mechanically compatible. It looks like Toyota Engineers (whom we hold in high esteem) replaced the crappy spring driven T-belt tensioner with a gas damper cyclinder, which is good, but they also moved the mounting features so that my old 92 compressor is too short, causing the pulley to misalign with the AC drive belt. I think my best course of action is to evacuate the system, install the new compressor, then recharge with R12 so that I don't have to dick around with any of the other components.