Electrical Troubleshooting Quiz, Oct. 22, 2013

Oct. 22, 2013
How to keep HVAC condensing units from icing up frequently during summer nights.

Last summer, several HVAC condensing units iced up frequently during the night. This caused a loss of cooling air. In the morning, as the temperature began to rise, the air conditioning was inoperable due to thick ice. As a temporary fix, techs melted the ice away each morning with electric heat guns and gas torches.

The units are a bit old, but your HVAC contractor's test reports show they meet spec and are mechanically sound. Based on this, your plant manager says the only logical conclusion is the units are undersized. He's planning to order bigger ones as direct replacements.

What should you do before the plant manager submits the capital request to the corporate office?

Actually, several other logical conclusions are possible. Your plant manager's expensive solution will have several negative consequences. And it will make the problem worse.

You can look for and solve energy leaks to reduce demand. But the most likely cause is a control problem. Properly set thermostats should prevent ice-over. Sometimes, individuals feel too hot so they adjust the thermostat all the way down as if this will make the unit produce cooler air. But it's just a switch. When the thermostat is all the way down, the unit doesn't get its normal shutdown period and then ice forms on the coils.

To solve this, install special thermostats that don't have an external adjustment. Leave the other units as dummy thermostats (not connected). The fact that people have something to adjust usually solves their "I feel too hot" problem.

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