Cold Weather Mechanical Systems Tip!

Protect your HVAC coils from freeze-up by doing this simple check


It has been awhile since our area and many other parts of the country as well have been subjected to subfreezing weather extremes in the teens and single digits for multiple days in a row. With the frigid temps, a quick check of the freezestats (the control devices that protect HVAC coils from freezing) is the best way to avoid bursting the coil from the expanding frozen water that could be laying dormant inside the coil.  During the post-freeze thaw is when the symptoms (a.k.a. the leaks) are most likely to appear. Obviously, it is too late then, as the coil will have already burst.

 Here are some simple things to check:

·     Make sure the freezestat is installed on the leaving side of the coil i.e. the side closest to the fan’s suction side. This avoids nuisance tripping from shots of cold outdoor air coming in contact with the entering side of the coil.


·      Check to see that the sensing element is serpentined correctly across the coil area that it is protecting. It must be done horizontally NOT vertically. If done correctly, this will keep the element from developing traps that cause the freezestat to not be able to detect freezing temperatures.


.      The setpoint on the freezestat should be somewhere between 34-36 degrees.

 .      Lastly, the freezestat should be wired directly in series with the magnetic starter coil of the unit fan so that on a fall in temperature to its setpoint, the freezestat will positively act to open the circuit to de-energize the starter coil. Thus, shutting down the fan and closing the AHU unit dampers.

About deltaautomation

President of Delta Automation, Inc. Working in industrial automation in excess of 30 years
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