The following figure shows the controller terminal block and terminal designation, internal controller relay actions, and connection purpose.
Figure 1. MR534 terminal block connections
The following table provides information about terminals 1 to 13 on the top terminal block. Sensors SN2 and SN1 are not polarity specific.
| Callout | Terminal block label | Terminal label | Description, function, and requirements | Wire size |
|---|---|---|---|---|
| 1 | Sensor inputs | SN3  |
Optional. Configure terminal 1 as a case averaging sensor with SN1, or as a defrost averaging sensor with SN2. | 0.34 mm2 to 1.5 mm2 (22 AWG to 16 AWG) stranded wires and twisted-leads cable. |
| 2 | SN2 |
Defrost temperature sensor. Connect either sensor lead from SN2. Connect the other lead to a C (common) terminal. | ||
| 3 | SN1 |
Case temperature sensor. Connect either sensor lead to SN1. Connect the other lead to the C (common) terminal. | ||
| 4 | C | Common terminal for the sensors. All low-voltage common terminals are connected. | ||
| 5 | RS 485 | + | The RS485 Modbus communications terminal block provides a restricted connection to the Modbus connections on an optional precision superheat controller (PSHC). Do not connect any other device to these terminals. | 0.14 mm2 to 0.34 mm2 (26 AWG to 22 AWG) stranded wires and twisted-leads cable |
| 6 | - | |||
| 7 | REF | RS485 Modbus signal reference | ||
| 8 | Analog output | AO+ | 0 VDC to 10 VDC or 4 mA to 20 mA analog output. Output is 0 VDC to 10 VDC for loads above 1K ohm and 4 mA to 20 mA for loads between 100 ohms to 500 ohms. | 0.34 mm2 to 1.5 mm2 (22 AWG to 16 AWG) stranded wires and twisted-leads cable |
| 9 | AO- | Common terminal for AO-. All common terminals are connected together. | ||
| 10 | LNC | Alarm  |
Alarm relay LNC. Line voltage output terminal. See Table 2 for electrical ratings. | 1.5
mm2 to 2.5 mm2
(16 AWG to 14 AWG) |
| 11 | LNO | Alarm relay LNO. Line voltage output terminal. See Table 2 for electrical ratings. | ||
| 12 | LC | Line
COM |
Line common. Alarm and evaporator fan and auxiliary relays share the LC terminal (connect to line voltage). See Table 2 and Table 3 for electrical ratings. | |
| 13 | LNO | Fan/Aux  |
Evaporator fan and auxiliary relay line voltage output terminal. See Table 3 for electrical ratings. |
The following table provides information about terminals 14 to 21 on the bottom terminal block. Do not apply any voltage to Binary Input terminals 19, 20, and 21. Connect only user-supplied voltage free contact switches to these terminals.
| Callout | Terminal block label | Terminal label | Description, function and requirements | Wire size |
|---|---|---|---|---|
| 14 | 120-240 VAC | L1 | Two terminals for supply power connection to the MR534 Controller. See the Supply Power row in Table 1. | 0.75
mm2 to 2.5 mm2
(18 AWG to 14 AWG) |
| 15 | L2 | |||
| 16 | LC | Line
COM |
Line Common. Defrost and compressor relays share the LC terminal (connect to line voltage). See Table 1 and Table 4 for electrical ratings. | 1.5
mm2 to 2.5 mm2
(16 AWG to 14 AWG) |
| 17 | LNO | Def  |
Defrost heater relay line voltage output terminal. See Table 4 for electrical ratings. | |
| 18 | LNO | Comp  |
Compressor relay line voltage output terminal. See Table 1 for electrical ratings. | |
| 19 | Binary input | C | Common terminal for binary inputs | 0.34
mm2 to 1.5 mm2
(22 AWG to 16 AWG) stranded wires and twisted-leads cable. |
| 20 | BI1 | Open or closed state detection. Connect to a user-supplied voltage free contact switch only. | ||
| 21 | BI2 |