What capability do certain Honeywell fan/limit control switches have?

• A. Only regulate a single-speed fan operation.
• B. Operate a circulating fan motor at two speeds and provide high temperature limit control.
• C. Provide power to the furnace blower without limits.
• D. Measure ambient humidity.

Answer: (B)

The key idea is that these Honeywell fan/limit switches combine two functions in one unit: they control the circulating blower at two speeds and they provide a high-temperature safety limit. The two-speed control lets the circulating fan run quietly at a low speed for steady air distribution, or ramp up to a higher speed when more air flow is needed during a heating cycle. At the same time, the high-temperature limit acts as a safety switch that opens if the furnace gets too hot, cutting power to the blower (and protecting the system from overheating). This dual capability is what makes this type of switch distinctive. It isn’t just a single-speed controller, it isn’t a humidity sensor, and it isn’t a feature that powers the blower without any limit.