International. Considering that the accuracy of contact-type temperature thermometers is superior to infrared temperature guns for performing mobile air conditioning diagnostic work, contact-type units have a high degree of accuracy, but precautions should be taken when using them (especially when connecting them to lines) to ensure accuracy.
Otherwise, it is possible to get readings that easily deviate from 5° to 10° and that can lead to an incorrect diagnosis.
To understand how this is possible, we must first look at how the connectors are designed. The units used in the MACS Update Clinic on March 30 have two long and flexible connectors that allow access to places that are difficult to access. At the top of the connectors is a depressant that is controlled with the thumb and has a spring that pushes it up.
Image 1. Thumb-operated depressant used to attach the connector to an A/C line.
At the bottom is a hard piece of plastic that measures about 3/4 inch wide.
A flexible cable connects the depressant to a small steel rod at the bottom that protrudes through the plastic piece. The steel rod is bent on an L-shaped hook with a slight curve.
To connect to an A/C line, the thumb is used to move the depressant down and the L-shaped hook is placed below the line. The depressant is then released and the hook secures the line firmly against a slightly circular area that is cut into the plastic piece. In this area of the plastic part there is a small splinter of metal which is the sensor element.
Image 2. The metal sensor element is indicated by the arrow.
The sensor element must have good contact with the line, otherwise an inaccurate temperature reading will result. This means that the lines being tested must be cleaned of grease and dirt before making the connection. Also, if a line is painted, it is best to take a piece of emery cloth and remove the paint in the area where the connection is made to ensure a good connection.
Sometimes the sensor element can be pushed a little inward and will not make good contact with an A/C line to which it is subjected. When that happens, it is necessary to take something that is flat and place it under the sensor element and carefully lift it, slightly, to place it in a position that makes proper contact with the A/C line.
Image 3. A small screwdriver is used to carefully lift the sensor element.
These contact temperature thermometers are precision tools and it takes a bit of practice to achieve a level of comfort when using them. It reminds me a bit of when I started using micrometers and comparator calibrators years ago when I was working on engines.
Check back next week and we'll cover a few more tips on using it.
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* Author: Richard Hawkins, MACS contributor.
MACS – Association of Mobile Air and Climate Systems.
