UV Light in an Air Handling Unit

May 5, 2020
Tech Tuesday

Face masks, hand sanitizer, and toilet paper – all things that are in high demand as of more than a month ago. Perhaps one other thing that may be in high demand is UV lights in the HVAC world, as UV light helps to disinfect air and surfaces. Not too long after the start of this viral pandemic, I got a tech call from someone that needed help finding a relay device to turn on and off the UV light in their air handling unit. The reason: they don’t want to get a sunburn or would rather not wear sunglasses to maintain the air handling unit.

Well, this is a new one out of the 5 years and nearly 6,000 calls that I’ve taken! I thought it worthy to write in a Tech Blog entry as well, so here you go. After talking for a little while to this caller about what kind of relay was needed, we formed a list of requirements:

  1. 10A contact rating
  2. 120Vac powered
  3. Can sense when the air handling unit service door is taken off
  4. Uses low voltage as the sensing voltage

After the third bullet point, I knew what was needed, so I steered this individual toward our Closet Light Controlling relays with a magnetic reed switch – specifically, models CLC212 and ACLCMAGSM.

However, in typical applications of the CLC212, when the door is open, the light turns on. This application needed to work in the opposite way – when the door opens, the light turns off. With this understanding, two options arise: use the CLC212-NC, as it will act opposite of the CLC212 or make sure to use a “Form C” magnetic reed switch, like the one I mentioned above.

When using a Form C magnetic reed switch, the installer has access to a normally open or normally closed contact on the switch. With the normally closed contact, one can effectively invert the logic so that when the door opens, the light then turns on. Easy peasy! Why use the Form C switch and not the CLC212-NC? Well, the CLC212 is easier to come by compared to the “-NC” version, making it simple if more air handling units need UV lights to turn on and off in the future.

So, there you have it – using a CLC212 and ACLCMAGSM to control the UV light in an air handling unit. It was an honor to help that individual and the same goes to anyone else that needs help. Feel free to email or call in for assistance when choosing any one of our devices!


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About the Author

Meet Samuel Klennert – you can call him Sam. He was born and raised amongst the farmland of Indiana, which included corn, soybeans, and sometimes wheat. Sam graduated from Purdue University with a Bachelors degree in Electrical and Computer Engineering Technology in 2015. He has a focus in analog circuitry and power electronics, but he’ll give software a try from time to time – just not that digital witchcraft!

Outside of work, Sam enjoys outdoor activities including (but not limited to) hiking, mountain biking (or just really-big-hill biking), and camping. Call Sam for tech support today – he’ll give his best effort to any task at hand!