Honeywell ythx9421r5101ww/u Prestige Iaq Thermostat

Product Description

The HONEYWELL ythx9421r5101ww/u is a hardwired, programmable IAQ thermostat designed for residential and light commercial HVAC systems requiring multi-stage control and indoor air quality integration. Operating on 18 to 30 VAC at 50/60 Hz, it supports up to 3 heat and 2 cool stages for conventional systems and up to 4 heat and 2 cool stages for heat pump configurations. The unit features an 8.06 square inch color touchscreen display and a 7-day programmable schedule, giving HVAC technicians precise control over system operation and occupant comfort settings across the full work week.

This thermostat is suited for residential and light commercial forced-air systems, including gas, electric, and heat pump applications. It accommodates both conventional and heat pump changeover modes, with auto and manual changeover selection. The extensive terminal block — covering R, RC, RH, C, W, W2, W3, Y, Y2, G, U1 through U3, S1 through S4, and accessory terminals A through D — makes it appropriate for systems with dehumidification, ventilation, or zoning accessories tied into the IAQ setup. HVAC technicians installing multi-stage or dual-fuel systems will find the terminal count sufficient for complex wiring layouts.

Key Features

• 7-day programmable scheduling with auto and manual changeover modes
• 8.06 square inch color touchscreen display for on-wall control and status visibility
• Supports up to 3 heat / 2 cool conventional or up to 4 heat / 2 cool heat pump stages
• Hardwired power source operating at 18 to 30 VAC, 50/60 Hz
• Extensive terminal designation set supporting IAQ accessories, zoning, and ventilation integration
• Screw terminal electrical connections for secure, code-compliant field wiring
• Heating setpoint range 40 to 90 degrees F; cooling setpoint range 50 to 99 degrees F

Compatibility

Designed for use with conventional forced-air heating and cooling systems supporting up to 3 heat / 2 cool stages, and heat pump systems supporting up to 4 heat / 2 cool stages, operating on 18 to 30 VAC low-voltage control wiring.

Installation Notes

Installation should be performed by a licensed HVAC technician. Disconnect power at the air handler or furnace control board and at the condenser before removing the existing thermostat or making any wiring connections. Verify that system supply voltage falls within the 18 to 30 VAC operating range before energizing. Screw terminal connections must be secure and correctly landed per the system wiring diagram; incorrect terminal assignment on multi-stage or heat pump systems can result in equipment damage or improper operation.