Ruud U802VA050317MSA Error Code *T085_F: Suction Line Temp Thermistor Failure (Transient, Two-Stage Only)
What Does Code *T085_F Mean?
Fault code T085_F on the Ruud U802VA is a transient, two-stage-only fault (*T085_F). It indicates that the suction line temperature thermistor — used by the Electronic Expansion Valve (EXV) system for cooling-side refrigerant superheat control — has failed or produced an out-of-range reading.
The EXV system on two-stage models controls refrigerant flow through the cooling coil. The suction line thermistor measures refrigerant temperature at the compressor suction line, and this data combined with suction pressure allows the EXV to compute superheat and control refrigerant charge distribution. When this thermistor is unavailable, the EXV may default to a fixed position, reducing cooling efficiency.
Because this sensor is part of the cooling system rather than the gas heating system, the U802VA will continue to heat normally with T085_F active. The T (transient) prefix confirms this was an intermittent observation. The fault is logged in the IFC and can be reviewed via the Bluetooth contractor app at the next service visit.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Faulty suction line thermistor | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Schedule a service call with an HVAC technician who holds refrigerant certification — this sensor is part of the refrigerant system
- A technician should inspect the thermistor connector and wiring at the next cooling system service appointment
- This fault applies only to two-stage U802VA models with a connected EXV cooling system
✓ Verified against manufacturer service manual — March 2026