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Old 06-16-2014, 07:15 AM   #18 (permalink)
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Originally Posted by oil pan 4 View Post
Its looking like with the 50/50 CO2/R-404a mixture I am getting almost a 1psi change for every 10F in temperature change.

I did a test like this on tires if purged and filled my self with 95% nitrogen back in 2006 and saw something like a 1.5 psi change for every 20F change.

So the CO2/R-404a mixture only changes pressure with temperature slightly more than nitrogen. Nitrogen according to some people doesn't change pressure as it heats up.
Yes, some folks believe that old wive's tale.

But I disagree about the gases behaving differently.

The Ideal Gas Law predicts a 12F change for every psi change, and 18F for 1 1/2 psi. Looks like good correlation there for the data you are getting regardless of the gas. (Keeping in mind you are only able to measure the pressure to 1/2 a psi.)

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