Finally after failing to reseal my AC compressor the first time, I have installed a replacement used Denso compressor that is now functioning properly. The AC is conversion from R-12 to R-134a. Toyota TSB confirmed that no dramatic changes are needed for the Denso 10PA compressor for conversion, just changing dryer o-rings and dryer itself. However, the TSB says that R-134a operating pressures should be higher than R-12. Does anyone know how much? I am too cowardly to take the pressure higher than 230PSI on the high side. I have no idea how much higher it should be. My AC vents are putting out 60 degrees on 90 degree days. So not very good, but at least functioning ok. Any idea what the pressure ought to be?
r134a vs r12 pressures Anyone Know?
- Thread starter Kurtatron
- Start date
Depends highly on ambient temperature.
A quick search for "R-134a pressure chart" should have you there.
A quick search for "R-134a pressure chart" should have you there.
It's the ratio between high and low that's important. How low does the low side get?
Roughly 2.2x ambient temp. A 100f day should be close to 220 psi
What's the r12 capacity?
Single: 35 oz.
Dual: 44 oz.
Dual: 44 oz.
What type of oil is in it? Did you just put used compressor on without changing the oil?
Charge by weight not pressure. Try to use the same amount of R-134a as is specified for R-12, or a small amount less if the high side pressure gets too high.
Charge by weight not pressure. Try to use the same amount of R-134a as is specified for R-12, or a small amount less if the high side pressure gets too high.
Conventional rule on R12 to R134a is take the factory R12 charge weight, and multiply by .8
80% of the R12 capacity
Run and evaluate pressures from there
80% of the R12 capacity
Run and evaluate pressures from there
Only a couple of years ago, I did a complete R-134a conversion on my '88 Supra. I saw high side pressures around 225psi on the hot day when I filled it. Low side was 35psi at idle, but 15psi at 2krpm. The high-side pressure did not go up with engine speed.
If you're looking at the same Toyota TSB I am, they understate how much refrigerant you should really use. For the Supra, they spec 650g. I put in about 750g and it works quite well. My friend who deals with AC for a living says that's typical. As long as your low side pressure isn't too high, add the extra 100g.
Your system should have a high-pressure cutoff switch, so don't worry about going too high as it will save itself.
One note on measuring: you should check vent temperatures with the AC on max and driving around 35mph. The automagic system in my Supra normally aims to keep the air vent temperature around 60F unless the system is set to max. With the outside air at 92F, I got 44F vent air temperature, which is perfect.
mk378 said it right - charge by weight not pressure. Pressure is related to temperature not amount of refrigerant (once you get some in there), until you badly overcharge it.
If you're looking at the same Toyota TSB I am, they understate how much refrigerant you should really use. For the Supra, they spec 650g. I put in about 750g and it works quite well. My friend who deals with AC for a living says that's typical. As long as your low side pressure isn't too high, add the extra 100g.
Your system should have a high-pressure cutoff switch, so don't worry about going too high as it will save itself.
One note on measuring: you should check vent temperatures with the AC on max and driving around 35mph. The automagic system in my Supra normally aims to keep the air vent temperature around 60F unless the system is set to max. With the outside air at 92F, I got 44F vent air temperature, which is perfect.
mk378 said it right - charge by weight not pressure. Pressure is related to temperature not amount of refrigerant (once you get some in there), until you badly overcharge it.
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What is the outside temp? Is the suction line cold all the way back to the compressor?
