Rheem R802VA07542117MSA Error Code T084_F: Outdoor Air Sensor Fault
What Does Code T084_F Mean?
Fault code T084_F on the Rheem R802VA is a troubleshooting-level fault applicable only to two-stage models. It indicates that the outdoor air temperature sensor is reporting a faulty or out-of-range value. The two-stage R802VA uses an outdoor temperature sensor to inform staging decisions — the IFC can use outdoor temperature data to determine when high-stage versus low-stage firing is appropriate for optimal comfort and efficiency.
With the outdoor sensor unavailable, the furnace will still provide heat, but it may not optimize staging as effectively as it would with accurate outdoor temperature data. Because this is a T (troubleshooting) fault rather than an A (alarm) fault, it is a logged observation rather than an active lockout condition.
This sensor is typically mounted outside the home and connected back to the furnace via wiring that passes through the exterior wall. Causes of failure include physical damage to the sensor from weather exposure, corrosion or moisture in the outdoor wiring run, and a disconnected or damaged connector inside the furnace.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Failed outdoor temperature thermistor | Most common | ✗ Call a pro → |
| Damaged or corroded outdoor sensor wiring | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Schedule a service call — the outdoor air temperature sensor should be inspected, and the external wiring run should be checked for damage
- A technician should verify the sensor wiring has not been damaged by pests, physical impact, or UV exposure at the outdoor location
- This fault only affects two-stage R802VA models; a technician should use the correct outdoor sensor part number for this model
✓ Verified against manufacturer service manual — March 2026