General Assist Technical Reference
KMCA Defrost Control
Defrost initiation and completion conditions
Technical reference for KMCA outdoor-unit heating operation
KMCA systems automatically initiate defrost when the required compressor operating-time and outdoor heat-exchanger temperature conditions are met. Defrost ends when either the outdoor heat exchanger reaches the release temperature or the maximum defrost operating time is reached.
Important: Defrost is a normal heating operation. During defrost, heating output may temporarily reduce or stop while the outdoor coil is cleared of frost.
1. Conditions for starting defrost
For normal defrost operation, the controller evaluates both compressor integrating operation time and the outdoor heat exchanger temperature.
| Compressor integrating operation time | Defrost start condition |
|---|---|
| Less than 25 minutes | Defrost does not operate. |
| More than 25 minutes | Outdoor heat exchanger temperature is ≤ -17°C when outside air temperature is ≥ -10°C. |
| Outdoor heat exchanger temperature is ≤ outside air temperature - 7°C, or outdoor heat exchanger temperature is ≤ -20°C when outside air temperature is < -10°C. |
Practical interpretation: A KMCA will not commence a normal defrost during the first 25 minutes of accumulated compressor operation. After this period, the outdoor heat-exchanger temperature must also satisfy the applicable low-temperature condition.
2. Integrating defrost conditions
The service information also specifies integrating defrost criteria for continuous and intermittent compressor operation.
| Continuous operation | Intermittent operation |
|---|---|
| More than 240 minutes compressor integrating operation time. | Less than 10 minutes* compressor continuous operation time. |
| Outdoor heat exchanger temperature is below -3°C. | Compressor OFF count reaches 40 times. |
* Intermittent-operation counting: If compressor continuous operation time is less than 10 minutes, the compressor OFF occurrence is counted. If any defrost operation occurs, the compressor OFF count is cleared.
3. Conditions for completing defrost
Defrost operation is released when either of the following conditions is met:
| Defrost release condition |
|---|
| Outdoor heat exchanger temperature sensor value becomes higher than +16°C. |
| Compressor operation during defrost has reached 15 minutes. |
Diagnostic note: A defrost approaching the 15-minute maximum repeatedly may warrant further investigation of outdoor coil condition, airflow, thermistor accuracy and refrigerant-system performance rather than assuming the defrost control itself is faulty.
4. Service quick reference
| Check | Reference |
|---|---|
| Normal defrost inhibited | Compressor integrating time is less than 25 minutes. |
| Normal defrost eligible | More than 25 minutes plus the applicable outdoor heat-exchanger temperature condition. |
| Long continuous operation | Integrating defrost reference: more than 240 minutes and outdoor heat exchanger below -3°C. |
| Frequent short cycles | For compressor runs shorter than 10 minutes, OFF occurrences are counted; reference threshold is 40 OFF counts. |
| Defrost release temperature | Outdoor heat exchanger sensor above +16°C. |
| Maximum defrost time | 15 minutes compressor operation. |
Technical reference: KMCA Defrost Operation Control.