We've been getting many questions on micron gauges that are ”going haywire” or reading in the micron range, even at atmospheric pressure.

First, micron gauges measure absolute pressure, so you can’t ”zero” them out.

They use tiny, very sensitive sensors that are calibrated to air, not refrigerant, so anytime refrigerant gets into the gauge, it's going to read a little wacky.

This often happens when pulling a vacuum on systems that previously had refrigerant in them, especially when pulling on the compressor because refrigerant pulls out of the oil as the pressure drops.

The best way to counteract these readings is to flow/purge with nitrogen prior to the vacuum, and just keep in mind that as refrigerant passes by the sensor, it may act a little erratic for a while. This will stop occurring as the refrigerant is removed.

If the gauge is reading incorrectly when open to atmosphere, you can just blow a bit of air or nitrogen into it to get it back to normal.

These erratic readings are not a problem with the gauge; they are an expected behavior when refrigerant hits the sensor.

—Bryan

P.S. – If you're interested in learning more about microns and micron gauges, please read this article.