So wählen Sie das PTC-Startrelais aus: Datenblatt und Auswahlhilfe für die QP2-Serie PTC-Startrelais

The PTC (Positive Temperature Coefficient) Starter Relay is a critical “gatekeeper” for your refrigerator, freezer, or wine cooler compressor. If your appliance is clicking but not starting, or the compressor feels hot to the touch, a failed QP2 relay is the most likely culprit.

This guide provides a technical deep-dive into the QP2-Series Datasheet to help you select the exact replacement based on resistance, pins, and power requirements.

1. The Science Behind PTC Starters

A PTC starter uses a ceramic disc that has low resistance when cold. Upon startup, it allows a high current to flow into the compressor’s start winding. As it heats up, its resistance increases drastically (almost instantly), effectively “disconnecting” the start winding once the motor reaches speed.

2. Technical Specifications: QP2 Series Resistance Table

Selecting the wrong resistance can lead to a “Short Cycle” or a complete failure to start. Use a multimeter to check your current part against these standard values:

Hinweis: “Abnormal Resistance” is defined as any value significantly higher than the ranges listed above or an “Open Circuit” (infinite ohms).

3. Critical Selection Criteria (The 3-Point Check)

A. Ohm Rating (The Most Important)

Typically the resistance (Ω) must match your original part. A QP2-4.7 cannot be replaced by a ​QP2-22​. 

If the resistance is too high, the compressor won’t get enough “kick” to start.

B. Pin Configuration

The QP2 series is available in:

• 1-Pin: Standard setup.
• 2-Pin / 3-Pin: Often used when a Run Capacitor is involved in the circuit.
  Ensure the replacement has the same number of spade connectors in the same positions.

C. Physical Housing Size

While most QP2 units are standard, always verify the plug diameter and spacing to ensure it fits onto the three-terminal “header” on the side of the compressor.

4. Troubleshooting: How to Tell if Your PTC is Bad

1. The Shake Test: Remove the relay and shake it near your ear. If it sounds like a box of broken glass (rattling), the internal ceramic disc has shattered.
2. The Multimeter Test: Measure the two holes where the compressor pins enter. If it reads “OL” (Over Limit), the circuit is broken.
3. Visual Inspection: Look for burn marks or a “burnt toast” smell near the terminals.

5. Frequently Asked Questions (FAQ)

How do I know which pin version I need?

Check your original wiring. If you have a wire connecting to a capacitor before the relay, you likely need a 2-pin or 3-pin version. 

If only one wire comes from the thermostat, a 1-pin is standard.

Can I upgrade to a “Hard Start Kit” instead?

While a hard start kit (relay + capacitor combo) can help an old compressor, it is always safer to replace the OEM-spec QP2 relay first to avoid putting unnecessary stress on the motor windings.

Does the QP2-4.7 work for all 1/4 HP compressors?

Generally, yes. Most 1/4 HP to 1/3 HP compressors utilize the 4.7 Ω resistance, but always verify with the sticker on the compressor housing.

Pro Maintenance Tip

If your PTC relay has burned out, it is highly recommended to also check the Overload Protector (the small circular component clipped near the relay). These two parts often fail together due to power surges or compressor stalling.