Micron Gauges Gone Wild

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.

Related Tech Tips

Condensate Drainage in a High Efficiency Gas Furnace
This article was written by HVAC/furnace technician Benoît Mongeau. Thank you, Ben.     High efficiency (or 90%, or condensing) furnaces use a set of two heat exchangers to retrieve more heat from the combustion products than their mid-efficiency counterparts. Because of this, they generate flue gases much colder than those of a mid-efficiency or […]
Read more
Underlying Problems That Get Missed
Today, I ran a service call with another tech where the previous tech had diagnosed an intermittent piston restriction. I read the history beforehand. For the past several years, there were many assorted comfort complaints and a lot of minor charge adjustments in both the summer and winter. It is worth noting here that the […]
Read more
Changing Refrigerants and Why it Matters to You
Graphic Courtesy of Danfoss On 8/8/17,  the United States court of appeals struck down an EPA phaseout of HFC refrigerants under the Clean Air Act on the basis that the Clean Air Act only gave the EPA the right to regulate ozone-depleting substances. However, many of us figured that the decision was likely to be […]
Read more

Leave a Reply

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

loading

To continue you need to agree to our terms.

The HVAC School site, podcast and daily tech tips
Made possible by Generous support from