Mars M39006 Fan Switch Open 90F Close 110F

Product Description

The MARS M39006 is a close-on-temperature-rise fan switch designed for use in heating and HVAC systems where automatic fan control based on supply air temperature is required. The switch opens at 90 degrees F and closes at 110 degrees F, providing a reliable 20-degree differential that prevents the blower from circulating cold air at startup or shutdown. It is a direct-acting thermal switch intended for installation by licensed HVAC technicians on residential and light commercial forced-air systems.

This fan switch is used in applications where a separate fan control function is needed, typically on gas furnaces, heat exchangers, or warm-air heating units. It triggers blower operation only after the heat exchanger reaches an appropriate supply temperature, improving comfort and system efficiency. The F-110-2 designation corresponds to its specific setpoint range and is a commonly referenced identifier in the field for this type of control.

Key Features

• Closes on temperature rise at 110 degrees F, opens at 90 degrees F
• 20-degree F differential for stable, chatter-free switching
• Prevents cold air delivery during furnace startup and post-cycle cooldown
• Direct-acting bimetal thermal switch construction
• Also referenced in the field as F-110-2 and F110-2

Compatibility

Designed as an OEM-style replacement fan switch for residential and light commercial forced-air heating systems requiring a close-on-rise control with a 110 degrees F close setpoint and 90 degrees F open setpoint.

Installation Notes

Installation should be performed by a licensed HVAC technician. Disconnect all power to the unit before removing or installing any fan control switch. Mount the switch in firm contact with the heat exchanger or plenum surface per the equipment manufacturer's specification to ensure accurate temperature sensing. Follow applicable local codes and the IFGC for gas-fired appliance service.

Technical Specifications

• Switch Action: Close on temperature rise
• Close Setpoint: 110 degrees F
• Open Setpoint: 90 degrees F
• Differential: 20 degrees F
• UPC: 685744390060

Standard Information

• Brand: MARS
• Manufacturer Part Number: M39006