i bought the hose with gauge test with (green,blue,yellow red) bars on it. when i test my pressure on my a/c it's all the way up to 90 (which is on the red bar) on the blue bar says "filled". will the pressure having it on red affect the coldnest of the A/C ??? what if i lose some pressure to meet the blue bar "filled" will it make a difference?

 

your best bet is to use some r134 or r12 manifold gauges, depending on what kind of refrigerant you have. once you hook your manifold gauges up to the high and low sides, your readings should be similar to what the ambient temp. is

example: if the temp out side is 70 degress, the low side will read close to 70, if not EXACTLY 70. if it does read 70 then your ac system is about right, not too low, not too high. if it reads over 70, its overfilled, if it reads anything lower than 70 such as maybe 60 or below, then you may be low on freon.