The 391937 and 391937/U are the same Honeywell/Resideo conversion kit

this specific mechanical LWCO is designed for millivolt service

Built to exact OEM specifications

Precision Sensing: Equipped with a 36" capillary and stainless steel sensing element for accurate remote temperature monitoring

If the Rheem-Ruud 47-102473-01 trips

Carrier HH79NZ039 Sensor 322027-701 The 391937 and 391937/U areThe Carrier HH79NZ039 is a Factory Authorized Part designed for high accuracy thermal monitoring in commercial and residential HVAC systems. This versatile thermistor is primarily utilized as an Outdoor Air Temperature (OAT) sensor, providing critical data to the economizer logic to determine free cooling eligibility. Beyond ambient air sensing, the HH79NZ039 is engineered for multi mode service, functioning effectively as a Supply Air Temperature