[DML] Re: R12 to R134 Conversion Help
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[DML] Re: R12 to R134 Conversion Help

Have you checked your gas pressures first to ensure that you've got a leak? Granted if there was work done up there something might have been damaged, but you should still check first. Using a simple Manifold Gauge, just go ahead and connect it to the High and Low sides of the ports on the back of the A/C Compressor, turn the A/C on with the fan on full speed, and then refer to page N:06:01 of the Workshop Manual and see if your High and Low pressures match what they're supposed to be based upon outside temperatures.

For the record, there is absolutely nothing at all to be afraid of when it comes to either servicing or retrofitting your car's A/C system since this is something that you can VERY easily do yourself in your own garage. The two biggest tools that you'll need are a Manifold Gauge and a Vacuum Pump. And since most auto parts stores have these things in their Loan-A-Tool Programs you don't even have to buy them!

Now in regards to your question, when it comes to an R134a Conversion, when done properly it WILL work just as efficiently as R-12. But there is one big drawback/key to doing this: You need to replace ALL of your old rubber hoses with new Barrier Hose. R-134a molecules are much smaller than R12 and can pass through the rubber walls of the hose. It's the exact same thing as a latex balloon that slowly shrinks and stops floating because the gas inside is slowly leaking out. The speeds are not the same though, of course. It might take about a year or two before you loose enough R-134a that you'll need a recharge. BUT if you compare the price of say 3 or 4 R134a recharges within a 10 year period compared to 1 or maybe 2 R12 recharges, it could technically run you much higher to convert if you don't do it properly.

Barrier Hose has a Neoprene membrane inside that prevents the gas from leaking out. The cost of converting over to R134a you can figure in at about $350 or so, with that price mainly just covering the hoses and some odds and ends, but countered by the cheaper price of R134a.

How hard is the conversion itself? Not very. If you were doing a complete rebuild of an R12 system that was exposed to the outside, you'd pretty much be doing the same amount of work to prep and repair that system that you would to convert it. You'd be flushing the system out, replacing the Accumulator, Orifice Tube, replacing the O-Rings and Seals, and then recharging the system. The only difference would be you'd just be buying different versions of some of the components that you're replacing. Not a big deal at all. Otherwise installing those Barrier Hoses are the only additional pieces that need replacement. Though if you're like me and have physical damage to your hoses (the Underbody sawed through the return line in the engine compartment because it wasn't tucked down far enough) and will be replacing them anyway, you're gonna have to buy new hoses anyways. So in my case an R-134a conversion is actually cheaper than maintaining R12 because the aftermarket hoses and refrigerant are both cheaper.

What is key to getting an R134a conversion to work? You need a Variable Orifice Valve, and you need to readjust your Low Pressure Switch. R134a & PAG Oil are more viscous than R12 & Mineral oil. As such you can develop increased High Pressures and when idling the A/C doesn't run as efficient in the same system. That is until you make these two key retrofits: The Variable Orifice Valve will allow Refrigerant to pass through it at lower pressures when the engine is idling. This not only allows the A/C system to continuously cool itself, but reduces the higher pressures, as well as keeps the occupants cold. Adjustment of the Low Pressure Switch is the other key as noted by the EPA's own guide to R134a retrofitting. Although with a VOV in place the adjustment will simply be minor (if at all). The other thing I mentioned here was the increased pressures on the High Pressure side of the A/C. Over the years people have warned about older compressors getting damaged by it, and advocate against retrofitting as a result. IMO it's a 6-of-one/half-a-dozen-of-the-other situation there. Higher pressures are bad, yes, but who knows what kind of damage the system already had let alone if the person who did the conversion even did it properly? People also complain about the efficiency of R134a compared to R12. R134a doesn't work best with old fashioned Orifice Tubes because they have a static pressure at which they spray. This is why your modern cars that use R134a don't use them anymore. They usually come with Expansion Valves that do the exact same thing as a VOV. I believe I've seen some DeLorean owners retrofit over to R134a and hit temperatures at idle in the low 40°F range with at least one who hit 38°F.

If you've still got refrigerant in your system you can either pump it out into another tank standing by so that you can pump it back in, or if converting you could see if any A/C shops in your area are willing to extract it and buy it off you if you're not going to reuse it.

As for filling your system up with either R12 or R134a, it's not a big deal. Once you've flushed the system out and have replaced all your parts, you just have to pull vacuum for 30 minutes to an hour (depending upon who you talk to), and then let the car sit for at least another half hour and ensure that your vacuum pressures haven't dropped. Then go ahead and charge it up as normal. Shove a thermometer into a duct vent, run the A/C full blast, watch your pressures and see that they match up with the chart on page N:09:01.

As for the Vacuum Pump and Manifold Gauges, like I say you can usually borrow them for free from most Auto Parts Stores. The only thing I would recommend is that you'll really want a vacuum that has it's own valve to seal it's hose off, and a Manifold gauge that also has a second valve on the yellow hose to connect to your refrigerant source. This way when you pull a vacuum you're not only purging the system inside the car, but also the line from your R12 or R134a source. Some people online say just simply cracking the hose open at the manifold once your disconnect it from the pump and move it over to the can to purge the air out of the line. Aside from not properly purging the manifold internally and still allowing moisture in, you also risk frostbite if that gas sprays out and hits your bare skin. So using a T-Fitting on the Yellow hose either on the manifold or vacuum side, along with a valve on the vacuum is pretty good insurance against loosing a finger or even an eyeball. To see a diagram of what I'm talking about, check out Figure 27 on page N:04:02.

There are still some other minor details here and there, but overall this should give you an idea enough that this is indeed something that you can do yourself.

vin 6585

--- In dmcnews@xxxxxxxxxxxxxxx, Mike <cambpd@...> wrote:
> Is there anyone in the Maryland area that I could get with on a weekend to help me convert my Delorean R12 a/c to R134?  I've done all my own work on my car, but am afraid to tackle an R134 a/c conversion.
> Last fall I drove  to PA. and had some welding work done on the  frame, in the rear and up front around the right fender.  On the way back to MD the a/c got weaker and weaker and finally shut off.  Now it seems I have a leak somewhere in the R12 system and am thinking that it should first be converted over to R134 before trying to troubleshoot the leak?
> Thanks!,
> Mike 
> VIN #5781
> [Non-text portions of this message have been removed]


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