Rheem R802VA07542117MSA Error Code *T084_F: Outdoor Air Sensor Fault (Two-Stage Only)

What Does Code *T084_F Mean?

Your two-stage, variable-speed R802VA07542117MSA can use an outdoor air temperature sensor so the Bluetooth Communicating IFC (Integrated Furnace Control) knows how cold it is outside. Outdoor temperature is useful context for a communicating, staged furnace: it lets the control make smarter decisions about staging and comfort instead of reacting only to the thermostat. Rheem lists T084_F as a two-stage-only fault, and it is logged when the outdoor thermistor reads outside the valid range, usually because the sensor has failed, its outdoor wiring is damaged, or a connector has corroded.

Because this is a monitoring input rather than a combustion-safety device, the furnace does not lock out and keeps heating. Rheem rates T084_F as low severity. What you lose is optimization by outdoor conditions, so the furnace runs on its default logic instead of adapting to how cold it is outside. Comfort remains, but the fine efficiency edge the outdoor reading provides is gone until it is repaired.

T084_F is the outdoor-air member of this board's air-temperature sensor group, alongside T081_F (return air) and T082_F (supply air). It is distinct from the cooling-system EXV superheat sensors, T085_F, T086_F and T088_F, and from T087_F, the control board's own temperature sensor. All are low-severity monitoring faults, not hard lockouts.

The outdoor sensor is unusual in this group because it lives outside the home and runs a long wire back to the furnace, so it is more exposed to weather, sunlight and pests than the sensors mounted inside the cabinet. That exposure makes wiring damage a more likely cause here than for the indoor sensors.

What You'll Notice

• The alphanumeric display shows "T084_F", or the LED blinks the code one digit at a time with a roughly three-second pause between digits
• The furnace still heats the home normally on every call
• Staging or efficiency may feel less optimized in very cold or mild outdoor conditions than before
• The fault stays logged in the Bluetooth contractor app after a power cycle
• No lockout occurs and comfort is largely unchanged

Common Causes

How This Is Diagnosed

A technician traces the outdoor sensor wiring from the furnace connector out to the sensor's exterior location, inspecting the run for pest damage, UV-cracked insulation, moisture intrusion and corroded splices. The thermistor's resistance is measured and compared against the expected value for the actual outdoor temperature; an open or out-of-range reading points to a failed sensor, while a good reading at the sensor but a bad one at the board points to a damaged wire or connector.

Because the long outdoor run is the weak point, connectors at both ends are reseated and checked before the sensor itself is condemned. This is informational only; this work is not homeowner-safe.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The code stays active and you want the furnace to resume optimizing by outdoor conditions
• The outdoor sensor or its exterior wiring shows visible damage, corrosion, or pest chewing
• The fault clears and returns with weather changes, hinting at moisture or an intermittent outdoor connection
• You want the correct two-stage outdoor sensor part confirmed for this model before a repair

✓ Verified against manufacturer service manual — March 2026