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π₯ KB ARTICLE: Fujitsu / ICP FF85215LT96M Furnace Diagnostics & Fault Codes
Document Type: Troubleshooting Guide
Applies To: FF85215LT96M (96% Gas Furnace Family)
Brand: Fujitsu / ICP
Last Updated: 2025-11-25
Source File: Fujitsu FF85215LT96M Furnace Diagnostics.pdf
1. SUMMARY
This article provides a full diagnostic reference for the FF85215LT96M furnace family, including normal operating codes, fault codes, causes, and corrective actions. It is intended for field technicians and tech support agents troubleshooting ignition, airflow, limit, flame sense, and communication issues.
2. TAGS
Furnace FF85215LT96M Diagnostics Troubleshooting Fault Codes Ignition Flame Sensor Pressure Switch Blower Motor IFC Control Board Fujitsu ICP 96% Furnace
3. NORMAL OPERATION CODES
| Code | Meaning | Notes |
|---|---|---|
| β | Standby | No thermostat call |
| h / H | Gas heat (low / high) | Normal heating |
| c / C | Cooling (low / high) | Cooling mode |
| cd / Cd | Cooling + Dehumidification | Reduced airflow |
| F | Continuous fan | G call from thermostat |
| hP / HP | Heat pump heating | Dual fuel systems |
| dF | Defrost heat assist | Low-stage heat during defrost |
4. FAULT CODE TABLE (SEARCH OPTIMIZED)
Ignition & Flame Sense
| Code | Description | Likely Cause | Corrective Action |
|---|---|---|---|
| 10 | 1-hour lockout | Multiple ignition failures | Correct issue, cycle power |
| 11 | Failed ignition | Gas off, bad igniter, dirty flame probe | Verify gas, clean flame rod, inspect igniter |
| 12 | Low flame sense | Weak microamp signal | Clean/replace flame sensor, verify ground |
| 13 | Flame lost | Flame not stable, gas supply issue | Check crossover, pressure, burners |
| 14 | Flame present w/ valve OFF (Critical) | Stuck gas valve, miswire | Replace valve, correct wiring |
Limit & Safety Switches
| Code | Description | Likely Cause | Corrective Action |
|---|---|---|---|
| 22 | Main limit open | Overheat, low airflow | Restore airflow, check motor, replace limit |
| 23 | HALC open | Missing jumper | Install jumper P1 pins 3β5 |
| 33 | Flame rollout open | Blocked HX, vent issues | Reset rollout, inspect burners + venting |
Pressure Switch Faults
| Code | Description | Likely Cause | Corrective Action |
|---|---|---|---|
| 44 | Low PS closed w/ inducer off | Stuck switch | Replace switch, check venting |
| 45 / 46 | Low PS open w/ inducer on | Vent blockage, long runs, inducer failure | Clear vent, repair inducer, install altitude kit |
| 55 | High PS closed w/ inducer off | Stuck switch | Replace, check wiring |
| 57 | High PS open | High static, vent blockage | Restore venting, check inducer |
Water / Condensate Faults
| Code | Description | Likely Cause | Corrective Action |
|---|---|---|---|
| 58 | Water circuit open | Missing sensor or wiring open | Restore sensor wiring |
| 59 | Water sensed | Blocked drain/trap | Clear drain, reposition sensor |
Blower / Motor / Communication
| Code | Description | Likely Cause | Corrective Action |
|---|---|---|---|
| 60 | Blower fault (can run) | High static, wiring, wheel issue | Reduce static, inspect wiring + wheel |
| 61 | Blower fault (cannot run) | Motor failure | Free rotor, replace motor |
| 66 | Blower overspeed | Excess static | Fix ducting, open registers |
| 68 | No blower comms | No 24V/120V, bad harness | Verify power at motor, inspect harness |
Control Board / Memory Card
| Code | Description | Cause | Corrective Action |
|---|---|---|---|
| d6 | HP conflict | Wrong motor or memory card | Install correct card/motor |
| d4 | No model data | Missing card | Install model card |
| d1 | Model data missing (Critical) | Corrupt or unreadable card | Replace card |
| 93 | Internal IFC fault | Control board failure | Replace IFC |
| 99 | Remote fault reset | β | Informational only |
5. LOCKOUT CONDITIONS
Soft Lockouts
-
5-minute lockout: low PS wonβt close
-
1-hour lockout: repeated ignition failures, unexpected flame, water sensed, dead blower declared
Hard Lockouts
Requires power cycle:
-
Internal IFC fault
-
Gas valve energized unexpectedly
-
Dead blower 4Γ during same heat demand
6. BLOWER MOTOR DIAGNOSTICS
Error 68
Β
Step 1 β Verify Power
-
120V present at pins 4 & 5
-
24V present at pins 3 & 4
Step 2 β Force Motor Test
-
Apply 24V to P5: motor should run at ~75%
-
No response β wiring or failed motor
Step 3 β Check for Overspeed
-
High static
-
Closed registers
-
Wheel loose
Step 4 β Internal Fault Check
-
Overheating
-
Rotor blocked
-
Replace motor if codes 60/61 persist
7. IFC (Integrated Furnace Control) NOTES
-
Always transfer original memory card to new IFC
-
DO NOT use cards from a different model
-
Confirm dipswitch settings match original board
8. FIELD TECH QUICK CHECKLIST
β Confirm thermostat call type (heat, cool, fan)
β Verify venting is clear
β Check pressure switch tubing for cracks/sags
β Inspect flame sensor microamps (goal: >1.5 Β΅A typically)
β Verify blower wheel is clean and tight
β Inspect condensate trap for blockage
β Match memory card to model
β Ensure proper polarity and grounding
