What refrigerant is used if the ambient temperature is 80 degrees and you measure a pressure of 103 psig?
Looking at the Temperature column along the left side, find 80 degrees and mark it. Then scroll right along that temperature line until you get to 103 psig. Wait, there is no 103 psig, there is a 101.9 and 161.2 psig. In this case, 103 is much closer to 101.9, so just use the 101.9 and go up to find the type of refrigerant used.
Did you get R-500? That's correct.
If R-123 is being used and the temperature is 95 degrees, what is pressure?
Take the R-123 column, mark it and go straight down. On the temperature side, we see that 95 degrees is not an option so we have to take both 90 degrees and 100 degrees, mark it and go straight across until you cross with the R-123 column. The temperatures intersect at at pressure of 2.6 and 6.3. Since 95 degrees is in the middle of the two know temperatures, we will need to take the middle number between 2.6 and 6.3. To find the middle, take 2.6 + 6.3 = 8.9, then take 8.9 /2 = 4.45.
The correct answer is 4.45. If you didn't know how to do the math, you could estimate from the answers given in the EPA exam that 4.5 is between 2.6 and 6.3.