Update A/C from r12 to 134a

[SidWell]

Is it possible to update an existing 78 A/C system from r12 to 134a refrigerant? What needs to be replaced?

[cygnusx1]

Get as much old oil out of the system as you can. Change as many o-rings as you can to buna material. Put in a new receiver-dryer. Pull vacuum on the system. Check for leaks. Add R134a and compatible oil. Put in 20% less R134a than specified for R12. Mine works great. It's an all-stock factory '76 AC system. You should have some bubbles in the sight glass. If you don't have bubbles, you put in too much R134a.

 

This is how I did mine and it has been working for about 8 years and about 25K miles with light A/C usage.

[zcarnut]

1. You have to flush out and change the oil in the ac system. Mineral oil is used in all R12 systems. However, mineral oil does not mix with R134a and therefore is not usable. Instead, use PAG oil (polyalkylene glycol) or better yet, polyol ester oil (ester oil for short). Ester oil mixes with and is compatible with mineral oil and ester oil can be used with both R12 and R134a refrigerants. Because of this, it is referred to as "retrofit oil".

 

2. Replace the receiver-drier with one that is designed for R134a systems (contains XH-7 or XH-9 type desiccant).

 

3. You should really change the compressor to one that is designed to be used with R134a. R-134a operates at higher pressures than R12. Older compressors have a tendency to fail when subjected to this increased pressure. In addition, the old Hitachi compressors are known to be somewhat leaky.

 

4. It’s also a good idea to change to a better (larger) aftermarket condenser with a higher flow capacity.

 

 

You should know that an air conditioning system converted to R134a will never cool as good as it did with R12. At its optimum a 134a retrofit will only get the cold air outlet temperature to within 3-5 degrees of the R12 system. R134a refrigerant is about 10% less efficient in removing heat than R12.

 

IMHO, do not waste your time with a R134a retrofit. Instead, get your MACS license so you can buy R12. Another alternative to use one of the “drop in” R12 replacement refrigerants like Freeze12 or AutoFrost.

[naviathan]

I just blew out my system with a dry air compressor and added the R134a oil and freon and went with it. Works great.

[cygnusx1]

Same here. When R12 hit platinum status, I read so many reports warning NOT to retrofit or mass destruction would occur!!! I figured that my system was dispensible at the time. If it breaks, I take it out and save weight, so I did the conversion as simply and basically as I could. The conversion kit box was about $39 at K-Mart at the time. Lo and behold! It works. No magic, no ghosts, no dragons, no wizards. It just plain has been working for eight years now. I think the R134a molecule is larger than the R12 which makes it tend to leak less. At least that's what I "heard". I had to file and drill the "conversion" fitting for the low pressure charge port but other than that, the boxed conversion kit fit the bill. I'ts not as cold as R12 but it's cold enough that the system cycles on and off properly to maintain cool cabin temps.

 

MOD:

I wired a manual switch in the HVAC circuit to turn on the compressor in VENT, DEF, HEAT, BI-LEVEL modes. This allows me to defog the windshield and get FRESH air with A/C if I want to. Make sure you keep the thermo switch in series with the manual compressor switch so the A/C can still cycle. I also wired the e-fan to come on whenever the A/C is on.

 

zcarnut probably describes the right way to do it but, I did it the backyard way and it still works ok. I think the Z compressors are pretty tough. They are definitely stout and heavy compared to modern units.

[ezzzzzzz]

Do a simple search of R12 vs R134. The R134 molecule is smaller. That's why it requires barrier hoses and O-rings. The R12 compressor should have the seals replaced too for the same reason. The condenser core must be larger (serpentine desired) because the R134 doesn't give up heat as easily as R12. The evaporator orifice should be swapped for R134 too. Of course, you can use an inexpensive retro kit and get acceptable performance. The freon will eventually leak out due to incompatible components and cooling ability will be less than a properly designed system. That is why so many think that R134 is inferior...not so.

[zcarnut]

Do a simple search of R12 vs R134. The R134 molecule is smaller. That's why it requires barrier hoses and O-rings. The R12 compressor should have the seals replaced too for the same reason. The condenser core must be larger (serpentine desired) because the R134 doesn't give up heat as easily as R12. The evaporator orifice should be swapped for R134 too. Of course, you can use an inexpensive retro kit and get acceptable performance. The freon will eventually leak out due to incompatible components and cooling ability will be less than a properly designed system. That is why so many think that R134 is inferior...not so.

 

It’s the chemical reaction between R134a and the older (nitrile) rubber o-rings that causes the o-ring to shrink and possibly leak. Molecular size has nothing to do with this. In addition, the higher operating temperatures of a R134a system have a negative effect on the nitrile o-rings. The HNBR o-rings recommended for use with R134a are fully compatible with R134a (and PAG oil) and have a much wider temperature range.

 

The problem with re-using the old Nissan Hitachi R12 compressor for a retro-fit is that no one makes any HNBR replacement seals, o-rings or gaskets for it.

 

Yes, leaks through the hoses can be reduced by switching to a barrier hose construction (which is basically a hose within a hose that limits the amount of the smaller R134a molecules that will slowly escape through the hose wall over time), but the leakage rate through even a non-barrier hose is so small it can be ignored. Again, no one makes a barrier-type hose that replaces the stock S30 hoses.

 

The ac systems used in the S30 Z cars do not have an orifice tube. They use a TXV system which utilizes a receiver-drier and an expansion valve. It's the CCOT systems that have an orifice tube and a accumulator.

 

The newer parallel flow condensers are much more efficient than the serpentine types. Instead of having a single large tube (to prevent an excessive pressure drop) like a serpentine condenser a parallel flow has many parallel tubes than are smaller in diameter. This allows more of the refrigerant to be in contact with the surface area of the tube which are themselves in contact with the cooling fins.

 

And another thing…it’s called R134a and not R134. The "a" suffix indicates a molecular structure of 1,1,1,2-Tetrafluoroethane. R-134 (without the "a" suffix) has a structure of 1,1,2,2-Tetrafluoroethane and is a compound that is not specially effective as a refrigerant.

 

Hey, I’m no ac expert… I just worked with a refrigeration engineer on a project two years ago and he really straightened me out.