Emerson 1E78-151 - User Manual

Questions and Answers

J
Jason DeleonJul 27, 2025
How to fix an Emerson 1E78-151 that is not producing heat?
- C
  Christine LeonardJul 27, 2025
  If your Emerson Thermostat isn't heating, try these steps: * Ensure the pilot light is lit. * Verify the SYSTEM Switch is set to HEAT and raise the setpoint temperature above the current room temperature. * Check for loose connections at both the thermostat and the system wires, ensuring they are securely attached. * If the heat works intermittently, it might be a furnace lock-out condition, and you should contact the furnace manufacturer or a local service person. * If the thermostat still doesn't work after these checks, it may require replacement.
M
michael60Aug 6, 2025
What to do if my Emerson Thermostat has no heat, cool, or fan?
- L
  lorihamiltonAug 6, 2025
  If your Emerson Thermostat isn't producing heat, cool air, or fan, start by checking the fuse or circuit breaker and replace the fuse or reset the breaker if necessary. Ensure the furnace power switch is turned ON. Also, make sure the furnace blower compartment door or panel is correctly installed to engage the safety interlock or door switch.
C
Colleen MooreAug 15, 2025
Why is my Emerson 1E78-151 Thermostat not blowing cool air?
- S
  sarahbradleyAug 15, 2025
  If your Emerson Thermostat is not cooling, first ensure the SYSTEM switch is set to COOL and the setpoint temperature is lower than the room temperature. Check all thermostat and system wires to confirm they are securely attached. If the issue persists, the cooling system may require professional service, or the thermostat might need replacement; in this case, set the thermostat to COOL and lower the setpoint below the room temperature as a diagnostic step.

Summary

Mounting and Wiring

Electric Heat or Single-Stage Heat Pump Systems

Configuration for electric heat or single-stage heat pump systems, including fan control.

Hydronic (Hot Water or Steam) Heating Systems

Setting the thermostat for hydronic systems, affecting heating cycle length.

Battery Location

Location and installation instructions for the required 2 "AAA" alkaline batteries.

Check Thermostat Operation

Fan Operation

Procedure to test the blower fan operation by switching the FAN switch.

Cooling System

Procedure to test the cooling system, including compressor delay and temperature adjustment.

Heating System

Procedure to test the heating system by adjusting temperature setpoints.

Operating Features

Temperature Display Adjustment

How to adjust the displayed temperature by +/- 3 degrees.

Display Backlight

Instructions to turn the display backlight ON or OFF.

Troubleshooting

Reset Operation

Procedure to reset the thermostat due to voltage spikes or erratic operation.

No Heat;No Cool;No Fan (common problems)

Common issues like blown fuses, power switches, or loose panels causing system failure.

No Heat

Diagnosing and resolving issues when the heating system does not operate.

No Cool

Diagnosing and resolving issues when the cooling system does not operate.

Heat, Cool or Fan Runs Constantly

Troubleshooting constant operation of heat, cool, or fan due to wiring or switch issues.

Furnace Cycles Too Fast or Too Slow

Addressing rapid or infrequent cycling rates influenced by thermostat location or system size.

Cooling Cycles Too Fast or Too Slow

Addressing rapid or infrequent cooling cycle rates.

Thermostat Setting and Thermostat Thermometer Disagree

Resolving discrepancies between set temperature and displayed temperature.

Blank Display and;or Keypad Not Responding

Troubleshooting a blank display or unresponsive keypad due to power or battery issues.

The White-Rodgers 1F78 is a non-programmable thermostat designed for heating and air conditioning systems. It is compatible with a wide range of 24-volt systems, including standard heat/cool, electric heat, heat pump (without auxiliary or emergency heat), and millivolt systems for floor or wall furnaces. It is not compatible with line voltage, multistage, or systems exceeding 30VAC, 1.5 Amp.

Function Description:

The 1F78 thermostat provides basic temperature control for heating and cooling systems. Users can set a desired temperature, and the thermostat will maintain that temperature by cycling the heating or cooling system on and off. It features a simple interface with up and down arrow buttons for temperature adjustment, and switches for FAN (ON/AUTO) and SYSTEM (COOL/OFF/HEAT) modes. The display shows the current room temperature, the set temperature, and indicators for system status (heat, cool, compressor lockout).

Important Technical Specifications:

Electrical Rating: 0 to 30 VAC, 50/60 Hz. or D.C.
Load per terminal: 0.05 to 1.0 Amps
Maximum Total Load (All terminals combined): 1.5 Amps
Setpoint Temperature Range: 45°F to 90°F (7°C to 32°C)
Operating Ambient Temperature Range: 32°F to 105°F
Operating Humidity Range: 0 to 90% RH (non-condensing)
Shipping Temperature Range: -40°F to 150°F
Power Source: 2 "AAA" alkaline batteries

Usage Features:

Non-Programmable: This thermostat does not offer scheduling features; it maintains a single set temperature.
Display: Features a clear digital display showing current room temperature, set temperature, and system status icons (snowflake for cool, flame for heat, flashing snowflake for compressor lockout). A "LO BATTERY" indicator alerts users when batteries need replacement.
Temperature Adjustment: Uses dedicated up and down arrow buttons for easy temperature setting.
System Mode Selection: A SYSTEM switch allows users to select between COOL, OFF, and HEAT modes.
Fan Mode Selection: A FAN switch allows users to select between ON (continuous fan operation) and AUTO (fan operates only when heating or cooling is active).
Simultaneous Heating/Cooling Setpoint Storage: The thermostat stores both heating and cooling setpoints, eliminating the need to re-enter them at the beginning of each season.
°F/°C Convertibility: The thermostat can display temperature in Fahrenheit (default) or Celsius. This feature is adjusted by clipping jumper W904 on the circuit board.
Electric Heat/Heat Pump Configuration: For electric heat or heat pump systems that require the thermostat to energize the fan on a call for heat, the GAS/ELECTRIC switch on the thermostat base must be set to the ELECTRIC position.
Hydronic System Compatibility: For hydronic (hot water or steam) heating systems, clipping jumper W905 on the circuit board will produce a longer heating cycle (approximately 1.5°F swing) compared to the default forced-air setting (just under 1°F swing).
Temperature Display Adjustment: Users can fine-tune the displayed temperature (within a ±3° range) to match an old thermostat by pressing the up and down arrows simultaneously for two seconds while the SYSTEM switch is in the OFF position.
Display Backlight (on some models): The display backlight improves visibility in low-light conditions. It can be turned ON (light activates for a short period after any button press) or OFF (default) by pressing the up and down arrows simultaneously for two seconds while the SYSTEM switch is in the HEAT position.

Maintenance Features:

Battery Replacement: The thermostat operates on 2 "AAA" alkaline batteries. A "LO BATTERY" message on the display indicates when batteries are low and need to be replaced. It is recommended to replace batteries annually with fresh "AAA" Energizer® alkaline batteries.
Reset Operation: In case of a voltage spike, static discharge, or erratic operation, the thermostat can be reset by pressing the up and down arrows simultaneously while moving the SYSTEM switch from OFF to HEAT. This also restores factory defaults.
Troubleshooting Guide: The manual provides a comprehensive troubleshooting section for common issues such as "No Heat/No Cool/No Fan," "Furnace Cycles Too Fast or Too Slow," and "Blank Display." It offers possible causes and corrective actions, including checking wiring, replacing fuses, re-lighting pilot lights, and verifying system settings.
Mercury-Free Design: This product does not contain mercury. If replacing an older unit that contains mercury, specific disposal instructions are provided to ensure proper handling and return to White-Rodgers.