Applicable Systems
FC-30
FC-51
FC-101
FC-202
FC-302
Symptoms
Controller displays E1, indicating the S3 sensor (defrost termination) is open or shorted. The controller cannot execute automatic defrost termination and will fall back to time-based defrost only.
Possible Causes
- Defrost termination sensor S3 wiring damaged or disconnected
- Sensor S3 has failed and reads open circuit or short circuit
- Terminal block corrosion causing intermittent connection
- Electrical noise or moisture in the sensor conduit
Troubleshooting Steps
- Step 1: Check the S3 sensor wiring at the controller terminals - verify continuity
Repair or replace damaged wiring between sensor and controller - Step 2: Measure S3 sensor resistance at room temperature - NTC type should read approximately 10k ohm at 25C
Replace sensor if resistance is out of specification - Step 3: Inspect terminal block for corrosion, moisture, or loose connections
Clean terminals and apply dielectric grease - Step 4: Verify sensor is properly positioned in the evaporator coil sensor well
Reinsert sensor to proper depth and secure
How to Reset
To reset E1: 1) Press any key on the controller. 2) The alarm will clear if the sensor is now reading correctly. 3) The controller resumes normal operation with S3-based defrost termination.
Common Replacement Parts
- 084G4000: Danfoss EKC 202C temperature sensor NTC 10k, 3m cable (Verify sensor type matches controller setting)
- 084G4002: Replacement terminal block for EKC series (Use only Danfoss-approved replacement parts)
Frequently Asked Questions
- Q: How do I know if the S3 sensor is faulty?
Measure the resistance across the sensor terminals. At 25C (77F), a good NTC 10k sensor should read approximately 10,000 ohms. An open circuit (infinite resistance) or short circuit (near 0 ohm) indicates a failed sensor.
- Q: Can the system run without the S3 sensor?
The system can operate temporarily with time-based defrost only, but this is less efficient and may cause coil icing. Replace the sensor as soon as possible.
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Source: Danfoss EKC 202C Controller Technical Guide, Form 202C-TG
Category: Refrigeration
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