924Board.org

[ZV]

Now that I've got the A/C blowing air out of the proper vents I've discovered that the air isn't cold.

Everything is working right but the compressor isn't engaging. My guess is that there is not enough R-12 in the system and that the safety switches are keeping the compressor from engaging.

I know that I need to replace the receiver/drier, evacuate the system, and change the oil in the compressor. Is there anything else that you would recommend I do? I plan to do the job myself rather than paying a shop to have it done.

Also, how does the R-134a do in terms of relative effectiveness when compared to R-12? Will the A/C still be sufficient to keep up with a 100+ degree Fahrenheit day?

ZV
_________________
Shifting is an art, learn it, love it, live it.

1976 Porsche 914 2.0 - Driving Restoration.
1987 Porsche 924S - Daily Driver

[gohim]

R134a conversions do not cool as well as the original R12 refrigerant does when the system was built for R12.

R134a operates at a higher pressure, and less gas is used, than with R12. Conversions usually use about 15%-20% less R134a.

Whenever servicing an ac system, all 0-ring seals between the hoses, and components should be replaced. Especially when converting from R12 to R134a, the seals originally installed in R12 systems are not compatible with the compressor oil used with R134a.

The complete system should be flushed to remove as much of the R12 oil as possible. The reason that you must replace the accumulator/drier, and flush the old oil out is compatibility. When the old oil and new oils combine, they form a gummy, jelly that can plug the system up.

You will need a vacuum pump to remove the air from the ac system after you have finished the conversion. If you have a decent size compressor, you can get a compressor powered vacuum pump from Harbor Freight for about $13.

Before you convert to R134a, I would suggest connecting an ac manifold gauge set to determine why your ac system is not cooling. If the addition of a small amount of R12 will get the ac working (if all of the R12 has not leaked out) then I would sugggest adding the R12, rather than the conversion, because you will be much happier with the way the system works.

The ac system in a 924/944 doesn't work that great with R12 to begin with. I would not expect the performance of an R134a conversion to work to my personal satisfaction.

[ZV]

According to the studies I've seen, R-134a is compatible with the same seals as R-12, and the Porsche service bulliten regarding converstion from R-12 to R-134a only mentions replacing the receiver/drier.

Seal compatibility at top.

I've got all the necessary evacuation hardware available from a friend who works in HVAC professionally.

Right now R-12 runs at least $60 per pound. If the system is working perfectly and just needs refridgerant, I will come out ahead financially by converting if I need more than 1.5 pounds of R-12.

ZV
_________________
Shifting is an art, learn it, love it, live it.

1976 Porsche 914 2.0 - Driving Restoration.
1987 Porsche 924S - Daily Driver

[gohim]

R134a gas particles are smaller than R12 gas particles. If the gas leaked from your ac system with R12 in it, what do you think is going to keep the R134a in the ac system after you drop it in?

As for the seals being compatible with both R12 and R134a, it's a know fact that seals made for R12 will not last when subject to R134a, and the compressor oil for it.

The reason why you need to flush the entire ac system is because the compressor oil is distributed throughout the entire ac system.

The accumulator/drier must be replaced for two reasons: #1 the filter media in the drier is contaminated with R12 compressor oil, and the will react with the R134a compressor oil, and #2 the filter media for R134a is different than that used with R12.

The hoses meant for use with R134a are made from a different material than those made for R12. Even if you replace all of the o-rings, if you have a hose that was marginal with R12, with R134a, the same hose will leak like a sieve.

talk to your friend that does auto ac systems for a living, and ask him what is required for a sucessful conversion.

[ZV]

Actually, the friend recommended R-22! We did a little digging and found that while R-22 was fluid compatible with R-12, it was much too high pressure to have it running in an automotive A/C system.

I'm fully aware of the reasons that the system will need a full evacuation (e.g. vacuumed out).

I'm going to try to get a manifold pressure guage for R-12 to see just how much is left in the system. Beginning to think that I ought to just take it to a shop and let them worry about it.

ZV
_________________
Shifting is an art, learn it, love it, live it.

1976 Porsche 914 2.0 - Driving Restoration.
1987 Porsche 924S - Daily Driver