Danfoss 120Z0399 Start Capacitor – 145-175 µF, 250 V, CSR Circuit

Danfoss 120Z0399 is an original start capacitor used in single-phase scroll compressors with CSR wiring (Capacitor Start – Capacitor Run). Its capacitance range is 145-175 µF and its voltage is 250 V.

Start Capacitor of the CSR Circuit: High Starting Torque for the Scroll Compressor

Single-phase compressors need high torque when starting against a loaded circuit. The start capacitor stays in the circuit only for the first few seconds, increasing torque by providing an additional phase shift to the motor; when the compressor reaches speed, the start relay takes it out of the circuit. The run capacitor, on the other hand, stays permanently connected and increases efficiency — the two are different parts and are not interchangeable.

When the start capacitor weakens, the compressor starts with difficulty, hums and trips the overload protector; the classic symptom is "the compressor does not run but is hot". During troubleshooting it should be assessed together with the start relay.

Technical Specifications (Official Danfoss Spare Parts Catalog)

• Model: Danfoss 120Z0399 | Type: Start capacitor, CSR wiring
• Capacitance: 145 – 175 µF
• Voltage: 250 V
• Housing: Metal (aluminum) cylindrical housing, terminals on top
• Use: In the circuit only at start-up — works together with the start relay

Compatible Danfoss Compressors

In the catalog, this capacitor is listed for two compressor families:

• MLZ / MLM series: 50 Hz (Motor Code 5) → MLZ/MLM 015 · 019 · 021 · 026  |  60 Hz (Motor Code 1) → MLZ/MLM 015 · 019 · 021
• H / HHP series: 50 Hz (Motor Code 5) → HRM025-047 · HRP025-047 · HRH029-040  |  60 Hz (Motor Code 1) → HRM025-034 · HRH031
• If a different capacitance is required: 120Z0400 for 161-193 µF (MLZ/MLM030, HRM051-054), 8173001 for 88-108 µF (MLZ/MLM038-042, HRM058-HLM081).

• 🔧 Verify your compressor's motor code. Versions of the same model number with different motor codes require different capacitors; check the motor code (5 or 1) and the frequency (50/60 Hz) on the label.
• ⚡ Discharge before removal: The capacitor stores energy; do not touch the terminals by hand before discharging them through an insulated resistor.
• Verify the capacitance by measuring: If the value read on the µF range of the multimeter is outside the 145-175 µF band (especially if it is low), the capacitor is worn out and the compressor cannot start.
• Check the start relay at the same time: If the relay is stuck, the start capacitor remains in the circuit permanently and bursts within a short time. Inspect the relay as well when replacing the capacitor.
• This is an original Danfoss part. Generic capacitors with the same capacitance are cheaper; the original is selected according to the motor characteristics of the compressor and is required for warranty coverage.