Automotive Air Conditioning Information Forum

I've have this set for a few years and it does both R12 and 134A systems as well as R22 home a/c. Since I usually evac and charge by weight I haven't paid attention to the actual numbers much, but what is the outer scale for?

That is the pressure in PSI

Ok so what are the scales of the respective refrigerants for? I assumed that was the pressure of each one, i.e. if you’re diagnosing an R12 system you read pressure on the R12 scale.

outer scale is PSI. Photo is not clear enough for me or I would explain which scale indicates saturated temp.

I wish I knew the answer to that question too. My scale is the same and I am assuming the same as you, (my Mastercool Gauge instructions are moot with no explanation either). Been looking all over the WWW for an answer to this but no success. BTW the picture is clear as heck to me so I don't know what that other poster is looking at.

The outer scale is clearly marked PSI. That is the pressure scale, and the one you use for testing.

The inner scales are clearly marked °F. They are Temperature scales. Simply a P/T chart on the gauge face for R12, R22 & 134a

I had to copy your image into Photoshop to sharpen it enough to see the scales. Let's imagine the needle is at the 30 psi position. The first scale (in light blue) is the R134a scale. The temp of the refrigerant at sea level is 35* F. The next scale (green) is the R22 scale. At the same PSI, the temp of the refrigerant is about 8*F. The next scale (red) at 30 PSI is about 33*F.

Dougflas wrote:Let's imagine the needle is at the 30 psi position. The first scale (in light blue) is the R134a scale. The temp of the refrigerant at sea level is 35* F.

This is important to know because?
And the lower the pressure the lower the temperature. So at 10psi the temperature is only 8*F. That would be great but at 10psi there isn't enough R134a in the system and it probably will blow warm?

Simply outstanding folks. The answer has arising. Thanks!