For effective system diagnosis, what must a technician always consider when using pressure curves?

When diagnosing a system using pressure curves, it is essential for a technician to consider both outside and inside temperatures. This is because pressure curves are directly influenced by the temperature differences between the indoor environment and outdoor conditions.

Understanding the pressures within the system under specific temperature settings helps technicians assess whether the heat pump is functioning as expected. The refrigerant pressure in the system is affected by the heat absorbed or rejected, which is a function of both the indoor and outdoor temperatures. For example, if the outside air temperature is significantly different from the established indoor temperature envelope, it can cause deviations from typical operating pressures, indicating potential issues.

In contrast, focusing solely on factors like indoor temperature, humidity, or line set length would not provide a comprehensive view of the system's performance. While those factors also play a role in overall system efficiency and effectiveness, they do not replace the importance of understanding the temperature conditions in both the indoor and outdoor environments when interpreting pressure curves for diagnostics.