- Or, change the SdF value to 0 during a defrost cycle and return to normal On/Off
operation. See the figure below.
Figure 10: Manual Defrost only: behavior when dI is set to 0
Control behavior when starting or stopping an automatically
enabled Defrost Off-Cycle
The controller enforces the following behavior:
• At power up, the initial Defrost Interval (dI) does not initiate a Defrost Cycle Time (dFt).
• A defrost cycle occurs at the beginning of each subsequent defrost interval.
• You can start or stop a defrost cycle using the SdF parameter or binary input (BIN).
• Starting a defrost cycle terminates the defrost interval (dI) and starts a new defrost cycle.
• Stopping a defrost cycle terminates the dFt and continues the current defrost interval (dI) until
the start of the next regular dI and defrost cycle.
Starting or stopping a Defrost Cycle using the SdF parameter
1. To start or stop a Defrost Cycle using the SdF parameter:
- Select a Start/Stop Defrost Cycle (SdF) parameter value of 1.
- Or, change the SdF value to 0 (zero) during a dFt to stop a defrost cycle and return the
control to normal On/Off operation. See Figure 11.
Starting or stopping a Defrost Cycle using the binary input (BIN)
1. To start or stop a Defrost Cycle using the Binary Input (BIN):
- Connect a momentary contact switch between BIN and COM on the T3 terminal block.
- Each time the momentary contact switch is pressed, the defrost cycle starts or stops
depending on whether the defrost cycle is running or not. See Figure 11.
A421 Series Electronic Temperature Controls with Off-Cycle Defrost Installation Guide18
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