Emerson 1F85U-42NP Thermostat Operation Manual

The Emerson 1F85U-42NP is an 80 Series non-programmable thermostat designed for single-stage or multi-stage heating and cooling systems, including conventional gas, oil, electric, or heat pump systems with up to 4 heat/2 cool stages. It features a clear backlit display, precise temperature control, and easy installation for battery-powered or hardwired setups. Below are the key specifications and operation instructions.

Key Specifications

• Type: Non-programmable, universal thermostat
• Compatibility:
  • Single-stage systems (gas, oil, electric, millivolt, 24V)
  • Multi-stage systems (gas, oil, electric)
  • Heat pump systems (up to 4 heat/2 cool stages, including auxiliary/emergency heat)
  • Heat only, cool only, or heat/cool systems
  • Not compatible with systems exceeding 30 VAC or electric baseboard heat
• Power Source:
  • Battery: mV to 30 VAC, NEC Class II, 50/60 Hz (2 AA alkaline batteries, Duracell or Energizer recommended)
  • Hardwired: 20-30 VAC, NEC Class II, 50/60 Hz with common (C) wire
  • Power Stealing Assist for systems without C wire
• Electrical Rating:
  • Terminal Load: 1.5 A per terminal, 2.5 A max combined
  • Rated Differentials (@ 6°F/Hr):
    • Heat (Conventional Gas/Oil/Electric): Fast 0.5°F, Medium 0.75°F, Slow 1.9°F
    • Cool (Central Air): Fast 0.9°F, Medium 1.2°F, Slow 1.7°F
    • Heat Pump (Heat/Cool): Fast 0.9°F, Medium 1.2°F, Slow 1.7°F
    • Heat Pump Auxiliary: Fast 0.5°F, Medium 0.75°F, Slow 1.9°F
  • Setpoint Range: 45°F to 99°F (7°C to 37°C)
• Display: Backlit LCD display, adjustable ±5°F
• Operating Conditions:
  • Ambient: 32°F to 105°F (0°C to 41°C)
  • Humidity: 90% non-condensing max
  • Shipping: -20°F to 150°F (-29°C to 65°C)
• Dimensions: 3-3/4” H x 6” W x 1-1/8” D
• Features:
  • Backlit display with large, easy-to-read temperature
  • Adjustable temperature display calibration
  • Compressor protection (up to 5-minute delay)
  • Keypad lockout option
  • Optional wall cover-up plate (F61-2663, 6-3/4” W x 4-1/2” H)
  • Energy-saving settings for temperature control
• Thermostat Configuration Options:
  • Single Stage (SS1): Gas, Oil, Electric, Heat Only, Cool Only, or Heat/Cool Systems - Maximum Stages Heat/Cool: 1/1
  • Multi Stage (MS2): Gas, Oil, Electric - Maximum Stages Heat/Cool: 2/2
  • Heat Pump (HP1/HP2): Single or Multi-Stage Compressor Heat Pump Systems, up to 4 Stages Heat/2 Stages Cool

Operation Instructions

Initial Setup

1. Insert Batteries: Install 2 AA alkaline batteries in the rear compartment, removing the battery tag to activate. Replace when “LO BATTERY” appears (approximately every 2 years).
2. Power On: If hardwired, ensure 20-30 VAC is supplied via the C terminal. The display should show the home screen. If battery-powered, the thermostat can operate without a C wire in some systems.
3. Configure System:

• Press and hold MENU for 8 seconds to access INSTALLER MENU (item 05).
• Select system type (Conventional or Heat Pump, AC0/AC1/AC2 for cooling stages, GA1/GA2 for gas heating), heat cycle rate (Fast, Medium, Slow), and compressor delay (item 50).
• For heat pumps, configure “Outdoor Equipment” (item 05) to select AC or heat pump and number of stages.
• Exit by pressing RUN or waiting for the display to return to normal.

Operating the Thermostat

1. Select Mode: Press SYSTEM to choose HEAT, COOL, AUTO, or OFF. For heat pumps, AUX mode is available for auxiliary heat.
2. Adjust Temperature: Press up/down arrows to set the desired temperature.
3. Fan Control: Press FAN to select AUTO (runs with heating/cooling) or ON (continuous).
4. Verify Operation:

• In HEAT mode, set temperature 1°F above room temperature; “Heat On” should display, and the system should start.
• In COOL mode, set temperature 1°F below room temperature; “Cool On” should display after up to a 5-minute compressor delay (indicated by flashing setpoint).
• In AUX mode (heat pumps), set temperature 3°F above room temperature; “Heat On Auxiliary” should display, and auxiliary heat should start.

Temperature Display Adjustment

1. Press MENU to access USER MENU.
2. Use NEXT to navigate to Thermometer Adjustment (item 07).
3. Press up/down arrows to adjust the displayed temperature by ±5°F to match the actual room temperature.
4. Press RUN to save and exit.
Note: Use a separate thermometer for calibration. Relocate the thermostat if near drafts, heat sources, or exterior walls (recommended placement: 1.5 meters above the floor, in a frequently used room like the living room or kitchen, not in direct sunlight or on an outside wall).[](https://www.manua.ls/emerson/1f85u-42np/manual)[](https://www.manuals.ca/emerson/1f85u-42np/manual)

Troubleshooting

• No Display: Check battery polarity or replace with fresh AA alkaline batteries. Verify C wire connection for hardwired setups. Reset by removing batteries for 2 minutes or pressing MENU and Back buttons simultaneously until the display blanks. If the display remains blank, check for loose wiring or a blown fuse.
  
• No Heat/Cool: Ensure SYSTEM is set to HEAT/COOL/AUX, setpoint is above/below room temperature (ideal range: 19-22°C), and circuit breaker is on. Check for compressor delay (up to 5 minutes, indicated by flashing setpoint). Verify wiring, especially O/B for heat pumps. If no response, bypass thermostat by connecting R, G, and Y wires to test system.
  [](https://www.manua.ls/emerson/1f85u-42np/manual)
• Furnace Cycles Too Often: In INSTALLER MENU (item 05), adjust heat cycle rate to MEDIUM or SLOW to reduce cycling frequency. If cycles are too short, check for incorrect anticipator settings or wiring issues.
  
• Inaccurate Temperature: Calibrate in USER MENU (item 07, ±5°F). Ensure thermostat is not near drafts, heat sources, or exterior walls. If temperature deviates more than 2°C from setpoint (dead band), verify system settings.
  [](https://www.manua.ls/emerson/1f85u-42np/manual)
• Fan Runs Continuously: Set FAN to AUTO. If fan persists, check wiring for shorts or incorrect connections (e.g., G wire). For heat pumps, ensure SYSTEM is not in AUTO mode if only heating or cooling is desired.
  [](https://www.manua.ls/emerson/1f85u-42pr/manual)
• Erratic Operation: Reset by removing batteries for 2 minutes or pressing MENU and Back buttons simultaneously. If issues persist, contact a professional technician at 1-800-284-2925.[](https://www.manualslib.com/manual/1190392/Emerson-1f85u-42np.html)

Installation Instructions

Warning: Thermostat installation and all components of the control system shall conform to Class II circuits per the NEC code. To prevent electrical shock or equipment damage, disconnect power at the main fuse or circuit breaker before installation. Do not operate the cooling system unless compressor oil heaters have been operational for 6 hours and the system has not been off for at least 5 minutes.

[](https://www.manuals.ca/emerson/1f85u-42np/manual)

Remove Old Thermostat

• Before removing wires, mark wires for terminal identification to ensure proper connections to the new thermostat. Take a picture of the wiring for reference. If replacing a thermostat containing mercury, handle carefully and dispose of properly per local regulations.
[](https://thermostat.guide/emerson/emerson-1f85u-42np-non-programmable-thermostat-installation-manual/)

Installing New Thermostat

1. Pull the thermostat body off the thermostat base. Do not force or pry to avoid damage.
2. Place base over the hole in the wall and mark mounting hole locations using the base as a template.
3. Move base out of the way, drill mounting holes. Use plastic screw anchors if existing holes are too large.
4. Fasten base snugly to the wall using mounting holes and two mounting screws. Leveling is for appearance only and does not affect operation.
5. Connect wires to the terminal block on the base using the appropriate wiring schematic. The RC/RH terminals are electrically connected, so no jumper wire is required for single-transformer systems; clip the jumper for two-transformer systems.
[](https://www.manualslib.com/manual/1190392/Emerson-1f85u-42np.html)
6. Push excess wire into the wall and plug the hole with fire-resistant material (e.g., fiberglass insulation) to prevent drafts.
7. Carefully line the thermostat up with the base and snap into place.

Battery Location

• Includes 2 AA alkaline batteries at the factory with a battery tag to prevent power drainage. Remove the tag to engage batteries.
• To replace, set system to OFF, remove thermostat from the wall, and install batteries in the rear along the top. Use premium brand AA alkaline batteries like Duracell or Energizer.
• If the home will be unoccupied for over 3 months and the battery level indicator shows low, replace batteries before leaving.

Power Stealing Switches

Leave switches in the “On” position for most systems. Details in the following table:

Thermostat Power Method	Switch Position/Description
Battery Powered, no 24 Volt system	Switches “On”, thermostat runs on batteries.
Hardwired with Battery Back-up, for 24 Volt systems with common connection from transformer to “C” terminal	Switches “On”, thermostat runs on power directly from transformer with battery back-up.
Battery Powered with Power Stealing Assist, for 24 Volt systems with no common connection	Switches “On”, thermostat runs on batteries and supplemental power drawn through heat or cool circuit.

Caution: Power Stealing Assist may cause issues on systems with high impedance electronic modules (e.g., furnace draft inducer motor running with no call for heat, furnace fan not turning off). If incompatible, set switches to “Off” to operate on batteries.

[](https://www.manualsbooks.com/emerson/thermostat/emerson-1f85u-42np-non-programmable-installation-and-operating-manual.html)