On A28 models, when the temperature rises to the dial setting, the circuit opens between red (R) and blue (B) of the low stage terminal (RBL). Simultaneously, the circuit closes between R and yellow (Y) of the low stage terminal (RYL). When the temperature rises further, the high-stage RB switch opens (RBH). Simultaneously, the high-stage RY switch closes (RYH). The reverse sequence occurs when the temperature falls. The differential is above the setpoint. See the following figure:
Figure 1. A28AK switch action
| Callout | Description |
|---|---|
| 1 | Temperature rise |
| 2 | Temperature fall |
| 3 | Low stage |
| 4 | High stage |