5 critical wire harness issues in heat pumps

After two years of stagnation, the heat pump market is growing again. Uncertainty around the supply of fossil fuels such as natural gas and oil is once more driving interest in these robust systems. Of course, heat pumps are only as reliable as the electrical components that control them. One of the less visible, but critical, elements in this system is the wire harness.

A wire harness forms the nervous system of the heat pump: it connects all components (i.e. sensors, compressors, valves and fans) and ensures they can ‘communicate’ with each other. For heat pump manufacturers to bring a reliable system to market, everything starts with the quality of the cables and wiring harnesses. These components play a crucial role in the system’s performance and durability. Below, we outline the 5 most common heat pump issues related to cable harnesses. For each problem, we also show how a specialised partner such as WAAK Cable Assembly can provide structural solutions.

1. How weather conditions impact heat pump wire harnesses: Moisture and temperature risks

Depending on the type, heat pumps often operate continuously under highly variable conditions. Outdoor units of air-to-water heat pumps and hybrid air-to-water systems in particular are exposed to:

• Temperature fluctuations: frost in winter, heat in summer 
• Moisture and condensation from rain and snow 
• UV radiation from sunlight 

Cables and wire harnesses are highly sensitive to these conditions. For example, moisture ingress can lead to corrosion. Even a minor deviation, such as an improperly applied heat shrink tube or sealing sleeve, can result in malfunctions or even complete system failure of the heat pump.

Challenges for manufacturers:

Achieving consistent, zero-defect wire harness assemblies with full traceability increases production complexity and raises costs.

How WAAK Cable Assembly addresses these challenges:

WAAK operates standardised production processes, watertight quality controls and employs experienced staff who guarantee precise wire harness assembly. WAAK Cable Assembly specialises in the production of high volumes of complex cable harnesses.

2. Why complexer heat pumps (such as R290 heat pump) increase cable harness complexity and design risk

Modern heat pumps contain an increasing number of electronic components. The latest generation operates with R290 (propane), an environmentally friendly natural refrigerant, which is becoming the standard due to environmental regulations. However, propane is a highly flammable gas and potentially explosive when mixed with air. As a result, many electronic safety components must be integrated into the system. R290 heat pumps include components such as electronic expansion valves (EEVs) that regulate refrigerant flow, leak detection sensors, and circuit breakers that immediately shut off power in case of leaks.

This increasing number of electronic components leads to:

• Increasingly complex wire harnesses with many branches 
• Multiple variants per model 
• Limited installation space 

As cable harnesses become larger, the risk of incorrect routing increases. At the same time, compact system design increases the risk of mechanical stress on cables. This can lead to cable breakage or poor contacts, potentially damaging insulation. In turn, this can increase the risk of short circuits.

Challenges for manufacturers:

Designing and producing complex, compact systems correctly, without errors, while maintaining sufficient flexibility.

How WAAK Cable Assembly addresses these challenges:

From supplier to the broader HVAC sector to second-tier supplier in the (e-)automotive industry: WAAK has extensive experience in assembling complex wiring harnesses. To guarantee a flawless result, WAAK integrates multiple quality controls into its production flow: electrical testing such as continuity tests, camera-based inspection, mechanical checks such as back-pressure tests, and water and gas tightness testing.

Finally, WAAK Cable Assembly has its own co-engineering department that thoroughly analyses customer assemblies, identifies potential issues and proposes improvements before production begins. In close collaboration with certain customers, WAAK has also co-developed solutions for customer-specific wire harness challenges.

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3. Heat pump wire harness installation errors: A hidden quality risk

Sometimes cable harness issues arise during final assembly. This is due to:

• Incorrect installation or fastening 
• Damage to the wire harness during installation 

Although these errors are not inherently related to the quality of the wire harnesses or components, they do affect how the final product is perceived in terms of quality.

Challenges for manufacturers:

Manufacturers have limited control over this. The only way is to prevent them from happening by giving your staff proper training and a thorough guidance.

How WAAK Cable Assembly addresses these challenges:

WAAK delivers plug-and-play wiring harnesses that are as user-friendly and installation-robust as possible. Based on our own experience and best practices built up over the years, we can often predict where critical points arise during installation. Our experienced co-engineering team takes this into account when analysing the customer’s cable harness design.

Customer case:

For customer SRG Group (Stelrad Radiator Group), which required a wire harness for its new radiator fan, we designed a plug-and-play pre-assembly that could be installed very easily and without potential errors.

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4. How dust, vibration, and wear affect heat pump cable harness reliability

Cables in outdoor units in particular are continuously exposed to:

• Dirt and dust
• Mechanical vibration
• Long-term load due to continuous use

These factors, linked to the operating environment and usage of the heat pump, accelerate ageing of cables (e.g. insulation materials) and connectors. This can lead to malfunctions, short circuits and system failure. Such conditions highlight the need for robust materials.

Challenges for manufacturers:

Selecting and using the right materials that can withstand these conditions over time.

How WAAK Cable Assembly addresses these challenges:

WAAK Cable assembly works with high-quality components and has the necessary material expertise. We have many years of experience in this field. Our co-engineering team evaluates wire harness designs: are the right materials used, is the component suitable for the application, and are all components compatible with each other, etc. More information can be found in our separate blog: ‘Most common wire harness assembly mistakes in HVAC’.

5. Scaling up heat pump wire harness production without losing quality

The energy transition and renewed interest in heat pumps are driving demand sharply upwards. This puts pressure on:

• Production capacity
• Lead times
• Cost efficiency

At the same time, quality requirements (= zero-defect) remain extremely high.

Challenges for manufacturers:

Scaling up quickly without compromising quality.

How WAAK Cable Assembly addresses these challenges:

As a social enterprise, we can scale up rapidly alongside our customers. We are capable of producing large volumes of wiring harnesses without compromising quality. This makes us a reliable partner in a fast-evolving market.

A strong example is our customer Thermia AB. They manufacture geothermal heat pumps and mainly operate in the premium segment. Suddenly, they were faced with a sharp increase in demand. WAAK was able to scale up alongside them without any impact on quality.

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Conclusion: High-quality wire harnesses are essential for reliable heat pumps

The combination of stringent quality requirements (zero-defect), increasing complexity, and strong exposure to external environmental factors makes wire harnesses critical and often underestimated components in heat pumps. If this is not properly considered during design, assembly and installation, it can negatively affect system performance. Producing such a product requires the necessary know-how, infrastructure and experience. WAAK Cable Assembly has all of this in-house and can produce and even optimise your wiring harnesses. A strong cable harness assembly partner is not a luxury, but offers strategic added value.