Fig. 21 — Defrost Control Board (DFB) Location
Defrost
The defrost control mode is a time/temperature sequence. There are two time components: The continuous run period and the test/defrost cycle period. The temperature component is provided by the defrost thermostat (DFT1) mounted on the outdoor coil.
The continuous run period is a fixed time period between the end of the last defrost cycle (or start of the current Heating cy- cle) during which no defrost will be permitted. This period can be set at 30, 60, 90 or 120 minutes by changing the positions of DIP switches SW1 and SW2 (see Fig. 23 and Table 13). The default run period is 60 minutes.
DIP
Switches
Jumpers
Fig. 22 — Defrost Control Board (DFB) Arrangement | Fig. 23 — DIP Switch Settings — Defrost Board |
Reversing valve control
The DFB has two outputs for unit reversing valve control. Op- eration of the reversing valves is based on internal logic; this application does not use an “O” or “B” signal to determine re- versing valve position. Reversing valves are energized during the Cooling stages and
Compressor control
The DFB receives inputs indicating Stage 1 Cooling and Stage 1 Heating from the space thermostat or unit control system (PremierLink); it generates commands to start compressors with or without reversing valve operation to produce Stage 1 Cooling (one compressor), or Stage 1 Heating (both compres- sors run).
At the end of the continuous run period, the defrost control will test for a need to defrost. On unit sizes
At the end of the unit defrost cycle, the unit will be returned to Heating cycle for a full continuous run period.
If the space heating load is satisfied and compressor operation is terminated, the defrost control will remember where the run period was interrupted. On restart in Heating, the defrost con- trol will resume unit operation at the point in the run period where it was last operating.
Table 13
Switch No. |
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| 1 | 2 |
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| 1 | 2 |
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| 1 | 2 |
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| 1 | 2 |
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| 3 |
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1 |
| ■ |
| ■ |
| 1 |
| ■ |
| ■ |
| 1 |
| ■ |
| ■ |
| 1 |
| ■ |
| ■ |
| 1 |
| ■ |
| On |
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0 |
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| 0 |
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| 0 |
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| 0 |
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| 0 |
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| Off | |||||
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| 30 minutes |
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| 60 minutes |
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| 90 minutes |
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| 120 minutes |
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| Fan Delay |
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23