Arkansas HVACR NewsMagazine September 2024

HVACR NewsMagazine September 2024

Tech News

Short Cycling By:Bryan Orr, HVAC School

system capacity and load (cooling or heating too quickly). Short cycling is a problem for many reasons, including poor temperature control, inadequate dehumidification, rapid component failure, and the list goes on and on. RAPID short-cycling can quickly cause contact and relay failure due to arcing and can be very damaging to motors. Let's look at some common conditions that cause short cycling. Safeties, Limits, and Pressure Switches Anytime there is an issue with the equipment that causes high temperatures or and high/low system pressures, there are often controls that shut the system off before a catastrophic failure occurs. Some common examples would be:

A friend of mine was telling me that a utility had the idea that they could reduce energy consumption by turning HVAC equipment on and off rapidly during times of high load. In their minds, wouldn't it be better to spread out the off time rather than keeping the system off for longer periods and allowing the space to become uncomfortable? The answer is a HARD NO on that one! Short-cycling is a condition where equipment goes on and off more than is optimal. Each time it goes on and off is called a cycle, and we (almost) always aim to keep run times long and cycles to a minimum. Sometimes short cycling occurs due to a system fault, and it sometimes occurs due to a mismatch between

Furnace limit switches

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• Compressor and other motor overloads • Refrigerant high, low, and loss of charge pressure switches