Operation - PENN Controls - A19BAC - A28AA - Electromechanical Temperature Control - A19 Coiled Bulb Control - A28 and A36 Multi‐Stage Temperature Control

The A19BAC controls have one enclosed SPDT switch. The red terminal is common. When the temperature increases, the circuit between R and B opens. Simultaneously, the circuit between R and Y closes.

Figure 1. Switch terminals

Note: The figure shows the direction of the switch action when the temperature increases.

The A28AA controls have two enclosed SPDT switches. The red terminal is common.

When the temperature rises to the dial setting, the circuit opens between R and B of the low stage terminal (RB_L). Simultaneously, the circuit closes between R and Y of the low stage terminal (RY_L). When the temperature rises further, the high-stage RB switch opens (RB_H). Simultaneously, the high-stage RY switch closes (RY_H). See the following figure.

The reverse sequence occurs when the temperature falls. The differential is above the setpoint.

Figure 2. A28 switch action

Callout	Description
1	Temperature rise
2	Temperature fall
3	Low stage
4	High stage