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Death, Vacuum Tube Contamination & Taxes: How to Diagnose and Clean


One thing is for sure in the HVAC industry: at some point you will run into contaminated sensors… just like death and taxes, guaranteed!  If your chosen micron gauge uses thermocouple vacuum tubes, read on! 

Let’s review the mechanics of thermocouple tubes.

The inside of a thermocouple tube has two wires in the shape of an X, and measureable gas surrounds those wires. 

The thermocouple element senses temperature  as the surrounding gas cools the thermocouple. Because the temperature of the wire is directly proportional to the amount of gas in the tube, we can infer pressure in the system. The thermocouple tube has an internal sensor that gives incorrect readings if contaminated. 

How do you know you might have a contaminated tube?

Sometimes your vacuum readings will over or underestimate the true vacuum, and/or there may be visible signs of oil or other contaminants in the tube. 


To check if the thermocouple tube is contaminated, you can use an otoscope to perform a visual inspection to see if oil is at the bottom of the tube. 

Cleaning thermocouple tubes is easy!

  1. Wearing safety glasses, hold the thermocouple gauge in a paper towel in your hand.
  2. Spray carburetor cleaner or acetone into the theromocouple.
  3. Shake out the oil, let it dry.
  4. Allow the thermocouple to dry completely before reinstalling in the system.

Death and taxes may not be simple, but diagnosing and cleaning thermocouple vacuum tubes, a piece of cake!

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