Outdoor Unit Menu / 13.5 – Defrost Control

The standard defrost mode of the outdoor unit is designed for use with a conventional indoor unit, meaning that during defrosting the outdoor unit operates at maximum power. However, this is not fully suitable when plate heat exchangers are used instead of a conventional indoor unit. At maximum compressor output during defrosting, the evaporating temperatures can drop to around −30 °C, which can be dangerous for a plate heat exchanger even under normal operation, when continuous water flow is ensured.

When the Defrost Control function is enabled (this function is enabled by default), the defrost process is replaced by a cooling mode with the outdoor unit fan switched off. In this mode, it is possible to set both the compressor frequency and the target evaporator temperature at which defrosting will be terminated. This function is therefore much gentler on the plate heat exchanger and significantly reduces the risk of freezing and cracking.

The standard defrost mode can switch very quickly between heating and defrosting and back again. When the Defrost Control function is activated, however, the system behaves similarly to switching from heating to cooling. In this case, there is always an approximately 3-minute pause between mode changes, which means that the entire defrost process is extended.

Maximum Frequency

– The maximum frequency to which the compressor will be set during defrosting. For the first 60 seconds of operation, the frequency is limited to 30 Hz; afterwards it increases to the configured value. This value may be automatically reduced if the T6 temperature drops below −5 °C during defrosting.

End Temperature

– Defrosting stops and normal heating operation is restored when the evaporator temperature rises above the set value. This indicates that all frost has melted.

EEV Value

– Setting of the electronic expansion valve (EEV) position during defrosting. The outdoor unit applies this setting only after approximately 3 minutes of compressor operation.

The Defrost Control function uses cooling mode for its operation. This mode may be limited by the minimum outdoor temperature, which for most air conditioners is around −15 °C. It is therefore very likely that defrosting will not start at such low temperatures. Nevertheless, we strongly recommend using this function, especially when a plate heat exchanger is used (a tube-in-tube heat exchanger is significantly more resistant to very low evaporating temperatures).

13.4 Quiet mode

13.6 Defrost trigger