Final answer:
The temperature splits observed suggest incorrect airflow through the indoor coil of the heat pump. The likely corrective action would be adjusting the airflow to achieve optimal temperature splits in both heating and cooling modes.
Step-by-step explanation:
When starting up a split system heat pump for the first time and observing temperature splits of 38°F in heat mode and 29°F in cooling mode at an outdoor ambient temperature of 60°F, these readings suggest that the airflow through the indoor coil may not be optimal. In heat mode, the expected temperature split should generally be between 20-30°F, and in cooling mode, it is typically around 15-20°F. Considering the high temperature splits, the most likely corrective action would involve reducing the airflow to decrease the temperature split in the cooling mode and potentially increasing it for the heat mode, depending on the specific heat pump's specifications.