LG Refrigerator Er rT: The Room Temperature Sensor Failed

Er rT means the ambient (room) temperature sensor returned an out-of-range reading. This sensor measures the air temperature of the room where the refrigerator is installed. LG's control algorithm uses this data to optimize compressor speed, defrost frequency, and energy consumption based on the thermal load the refrigerator faces from its environment.

Why the Room Temperature Matters

The refrigerator's cooling demand depends heavily on the ambient temperature. In a 68 degrees F kitchen, the compressor runs less frequently than in a 90 degrees F garage. LG's Inverter Linear Compressor adjusts its speed continuously to match demand — the room sensor is a key input to this speed calculation.

Without ambient temperature data:

• The compressor runs at a fixed default speed (usually medium-high) regardless of room conditions
• Defrost frequency reverts to a fixed schedule rather than adapting to humidity and temperature
• Energy consumption increases because the compressor does not down-regulate during cool periods
• In very hot environments, the default speed may be insufficient — gradual warming could result

The Practical Impact

For most homes with a kitchen temperature between 60-80 degrees F, Er rT causes minimal observable difference. The compressor's default operating mode handles this range adequately. You may notice slightly higher energy bills from the compressor not optimizing.

In extreme environments — a garage in summer (100+ degrees F) or a basement in winter (below 50 degrees F) — Er rT has more impact. The board's default assumptions do not match the actual environment, potentially causing insufficient cooling in heat or unnecessary energy consumption in cold.

Finding the Room Sensor

The ambient temperature sensor is mounted on the exterior of the refrigerator or just inside the machine compartment (rear lower area) where it can measure room air rather than the refrigerator's internal temperature. On some models, it is behind the base grille at the front bottom.

Unlike the internal sensors (FS, RS) which are inside the compartments, the room sensor must be positioned where it reads room air. If it is accidentally pushed against a warm condenser coil or a cold refrigerant line, it reads an incorrect temperature.

Testing the Sensor

1. Unplug the refrigerator
2. Locate the room sensor (check the tech sheet — it is often near the condenser fan area or behind the base grille)
3. Disconnect the 2-wire connector
4. Measure resistance at actual room temperature:
   • At 68 degrees F: expect approximately 5,000-6,000 ohms (standard 5K NTC)
   • At 80 degrees F: expect approximately 3,500-4,500 ohms
   • At 50 degrees F: expect approximately 8,000-10,000 ohms
5. Infinite or near zero = sensor failed
6. If resistance is correct but Er rT persists, check harness continuity to the main board

Sensor Replacement

1. Unplug the refrigerator
2. Access the sensor location (remove base grille or rear lower panel)
3. Disconnect the old sensor
4. Install the new sensor (model-specific, $8-18) in the exact same position
5. Important: ensure the sensor is in ambient air, not touching any refrigerator component. Mounting against the condenser, compressor, or a refrigerant line gives a wrong reading even with a new sensor
6. Reconnect, reassemble, plug in

Parts and Cost

Er rT Priority

Er rT is the lowest-priority LG refrigerator error code. The fridge cools, the freezer freezes, and ice production continues. The only impact is suboptimal compressor efficiency and fixed-schedule defrost. In a normal kitchen, you may not notice any difference at all.

Address Er rT when convenient — it does not require urgent service. The risk is only in extreme ambient conditions where the default compressor strategy does not match the environment.

Garage-Installed Refrigerators and Er rT

Garage installations are the environment where Er rT matters most. A garage can swing from 40 degrees F in winter to 110 degrees F in summer. Without the room sensor telling the board the actual ambient temperature:

• In summer: the default compressor speed may not compensate for the extreme heat load
• In winter: the compressor may not run at all if the garage temperature is close to the fridge's target temperature (the board cannot distinguish between a cold fridge and a cold room)

If your LG is in a garage and shows Er rT, prioritize the repair to maintain proper operation across seasonal temperature swings.

Linear Compressor Speed and Ambient Sensor

LG's Inverter Linear Compressor can operate at variable speeds — from a slow, quiet hum during low-demand periods to full speed during recovery (after door openings or in hot rooms). The room sensor is one of the inputs that determines the target speed. Without it, the compressor uses a fixed medium-high speed that is neither quiet during low demand nor maximum during high demand. Replacing the $8-18 sensor restores the intelligent speed control that makes the Linear Compressor efficient and quiet.

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LG refrigerator showing Er rT? Low priority in normal kitchens, but important for garage installations. We carry sensor replacements for a quick swap. Book sensor service.