4235 – THERMOSTAT (3H/2C, PROG)

Braeburn Premier Series programmable thermostat for heat pump systems up to 3 heat / 2 cool and conventional systems up to 2 heat / 2 cool, and it will also run 250-750 mV millivolt heating systems. It can be set up as 7-day, 5-2 day or non-programmable, and runs on 24 VAC hardwire or two AA alkaline batteries. Features include humidification and dehumidification control, programmable and circulating fan modes, adaptive recovery, pre-occupancy purge, commercial mode, keypad lockout and a multi-function dry contact input.

Specifications published by the manufacturer. Source: manufacturer documentation.

Specs

• StagingHeat pump up to 3H/2C; conventional up to 2H/2C
• Millivolt250-750 mV systems
• Programming7 Day, 5-2 Day or Non-Programmable
• Power24 VAC (18-30 VAC) or 2 AA alkaline (included)
• Electrical rating1 A max per terminal, 7 A total
• Control range45 F to 90 F
• Display range35 F to 99 F
• Accuracy+/-1 F
• Dimensions4.25" H x 5.12" W x 1" D
• Display size4.4 sq in
• BacklightAdjustable bright blue
• Auto changeoverYes
• Keypad lockoutYes
• Remote sensorsIndoor / outdoor
• Humidity controlHumidification and dehumidification
• Dry contact inputYes (multi-function)
• Commercial modeYes
• Warranty5-year

Do I need a C wire?

For almost any Wi-Fi or smart stat, yes. A screen, a radio and a relay board need continuous 24 volt power, and the C wire is that return path. Battery-only and power-stealing installs are where the nuisance calls come from, with stats that reboot, short cycle, or bump the blower for a second at a time to steal charge. If you only have four conductors at the wall, your options are to pull new 18/8, repurpose an unused conductor at both ends, or use an add-a-wire adapter at the board.

What is O/B and why does it matter?

On a heat pump, O/B controls the reversing valve. Most brands energize it in cooling, which is the O terminal. Rheem and Ruud energize in heating, which is B, and so do Weathermaker, Ameristar and residential Bosch air-source. Get it backwards and the system blows cold on a call for heat and hot on a call for cool. Confirm it off the wiring diagram on the unit rather than guessing by brand, because it varies inside product lines.

Will any thermostat run my system?

No. A communicating system of the ComfortNet, Infinity or Evolution type needs its own matched stat on a two-wire data bus, and a conventional 24V stat will not run it. Two-stage, dual fuel and heat pumps with auxiliary heat need enough terminals plus the right setting in the configuration menu. Millivolt and line voltage equipment take entirely different stats.

The thermostat screen is blank. Bad stat?

Check the board fuse and the float switch first. A blank display almost always means the 24 volts is gone, not that the stat died. A blown board fuse, a tripped condensate safety, an open blower door switch, or a rubbed-through wire in the attic account for most of them.