Bitzer SE-B2

What does Bitzer SE-B2 mean?

The SE-B2 is a basic BITZER compressor protection device that watches motor winding, discharge-gas and oil temperature via PTC sensors. If the preset temperature is exceeded, the device locks out immediately and stops the compressor. It also detects a broken sensor lead. It is the 24 V AC / 24 V DC version that replaced the older SE-B1.

Symptoms

• Compressor stopped and will not restart
• Protection-device relay has opened the safety chain
• Compressor was running hot before shutdown
• Device stays locked until power is interrupted

Common causes

• Motor winding, discharge-gas or oil temperature above the preset limit
• Break (open circuit) in the temperature-sensor lead
• Compressor overload or insufficient cooling
• Faulty or disconnected PTC temperature sensor

Diagnostic steps

1. 01

   Find and clear the fault first

   The device will not reset until the cause is found and corrected. Identify why winding, discharge-gas or oil temperature rose before attempting a reset.

2. 02

   Let the compressor cool

   Allow the motor and oil to return to normal temperature so the PTC sensors fall back within range.

3. 03

   Check the sensor circuit

   Verify the winding-temperature sensor wiring is intact; the SE-B2 also locks out on a broken sensor lead (Leiterbruch).

4. 04

   Unlock the device

   To unlock, interrupt the supply voltage to the protection device for at least five seconds, then restore power.

5. 05

   Confirm the device variant and supply

   Confirm the SE-B2 supply voltage variant (230 V, 115 V or 24 V) matches the installation before returning to service.

When to call a professional

All work on the compressor and the system it is built into must be carried out by trained, authorized specialists. If the device keeps locking out after cooling and a sensor check, the underlying over-temperature or motor fault needs qualified diagnosis. Electrical work on the protection device and safety chain, and any compressor internal fault, should be handed to a refrigeration technician.