Portable air, NOT a compressor

I'm not a chemist, I'm a mechanic. These are just the things I have learned about a/c systems // low side pressure 30 psi =a core temp of about 30 degrees. The biggest joke on new kids is when a customer came in with a a/c problem the old guys would bet on pressure in the system while the car was sitting, ( complaint would have to be not cold enough) and it would always be ambient temp. That's why Freon has been used as propellants in aerosol cans(or something close to that makeup)

did not print the whole chart but look at the 62,64 temps =63,64 psig its close to a temp=pressure

What you show is a chart describing the normal temperature/pressure relationship of an A/C system, which cycles the r134c through the gas and liquid state using a compressor, condenser, and evaporator. That's totally different than filling a container with r134c and observing the temperature/pressure relationship of the gas alone with nothing else acting upon it, as would be the case if you happened to fill a tire with it.

As I mentioned before, using Fahrenheit temperature units doesn't even apply to the gas law, so even if you did happen to find some relationship of that kind its purely coincidental.

dwalby said:

What you show is a chart describing the normal temperature/pressure relationship of an A/C system, which cycles the r134c through the gas and liquid state using a compressor, condenser, and evaporator. That's totally different than filling a container with r134c and observing the temperature/pressure relationship of the gas alone with nothing else acting upon it, as would be the case if you happened to fill a tire with it.

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The chart is absolutely correct however I believe there is a point missing in the discussion. You are dealing with Gasses and the Chart refers to a liquid in a sealed container. This could be in a can or in a charged AC system. for example Liquid Oxygen stored in a sealed container at room temperature would have a pressure of more that a 1000psi and thus not correlate with approximately the same temperature on the thermometer. It is mathematically predictable but just a coincidence that the Liquid Refrigerants temperature in degrees Fahrenheit and pressure in P.S.I roughly correlate.

CruSTy said:

The chart is absolutely correct however I believe there is a point missing in the discussion. You are dealing with Gasses and the Chart refers to a liquid in a sealed container. This could be in a can or in a charged AC system. for example Liquid Oxygen stored in a sealed container at room temperature would have a pressure of more that a 1000psi and thus not correlate with approximately the same temperature on the thermometer. It is mathematically predictable but just a coincidence that the Liquid Refrigerants temperature in degrees Fahrenheit and pressure in P.S.I roughly correlate.

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Hey Crusty, thanks for the little push here. Since Al didn't really explain what his table meant, I wasn't sure what he was presenting. Based on the context of his comments, I thought it was an auto repair guideline to evaluate the health of auto A/C systems. I now realize, thanks to your push, that the chart is actually a saturation table for r134c. So, at each given pressure in the table, it states the max temperature at which r134c will remain in the liquid state (or minimum temp at which it will remain a gas). Are we in agreement on that, I think so??? So my original claim that his table didn't represent the pressure/temperature relationship of r134c gas sitting in a tire at ambient riding temperatures was correct. The other chart I posted shows that at the normal pressures and temperatures expected of a tire, r134c isn't exactly an ideal gas, but its within about 10% of being an ideal gas.

But now that I understand Al's table, there is something about r134c that is questionable for emergency tire inflation purposes, and that's the fact that at 40psi, if the ambient temp is below 45F it will begin to turn back into a liquid (if I'm reading the table correctly). Al originally claimed the risk would be that at 90F the tire pressure would be 90psi, which isn't the case if we inflated the tire to 40psi at room temp. But at lower ambient temperatures we would run the risk of the pressure inside the tire dropping down below 40psi and I guess it would reach equilibrium at the max pressure at which r134c could remain a gas at the ambient temperature.

dwalby said:

But at lower ambient temperatures we would run the risk of the pressure inside the tire dropping down below 40psi and I guess it would reach equilibrium at the max pressure at which r134c could remain a gas at the ambient temperature.

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At normal room pressure uncontained the R134a will boil into a gas at any temperature above -14.9 deg F. It would work fine in the tire. That said I like my method in Post #30 of this thread. You can carry enough starter fluid in one small can to inflate many many many MC tires. Plus its way more fun to play with fire!!:flame:flame:flame Don't get me started on fun stuff you can do with starting fluid pardon the pun!!

CruSTy said:

At normal room pressure uncontained the R134a will boil into a gas at any temperature above -14.9 deg F. It would work fine in the tire.

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yes, that is true, but at normal room pressure our tire would still be flat

dwalby said:

but at normal room pressure our tire would still be flat

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Granted the r134a will not behave the same as air but Boyle's law still applies to the gas. If you inflate a tire at 70 deg F to 40 PSIG the pressure will drop proportionately to the temperature as shown in your chart. The tire will be low but not flat at 45 deg F. The refrigerant would not change to a liquid under these conditions. The tire cooling process is insufficient to remove enough latent heat to cause the state change from gas to liquid. If he wants to use refrigerant to inflate a tire roadside more power to hm. Fun with Mr. Science

CruSTy said:

Granted the r134a will not behave the same as air but Boyle's law still applies to the gas. If you inflate a tire at 70 deg F to 40 PSIG the pressure will drop proportionately to the temperature as shown in your chart. The tire will be low but not flat at 45 deg F. The refrigerant would not change to a liquid under these conditions. The tire cooling process is insufficient to remove enough latent heat to cause the state change from gas to liquid. If he wants to use refrigerant to inflate a tire roadside more power to hm. Fun with Mr. Science

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I think you might have missed my point, if the r134a is at normal room pressure, then our tire would be at 0 psig. As in the pressure inside the tire would equal the pressure outside the tire. I was just trying to point out that the low saturation temperature associated with 0 psig doesn't do us much good, since we need 40 psig in the tire for it to be useful. At that pressure the saturation temperature is around 45F, so we wouldn't have a lot of margin. Its pretty much an academic exercise anyway.

edit: the standard air already inside the tire would combine with the r134a, so the gas inside the tire would be about 25% standard air and 75% r134a, not pure r134a. The saturation temp of the combined gases would be high enough that we'd have enough margin even in relatively cool weather.