Final answer:
When a heat pump is operating in the heat mode, the suction line at the compressor will feel warm.
Step-by-step explanation:
When a heat pump is operating in the heat mode, the suction line at the compressor will feel warm. In the heat mode, the heat pump transfers heat from a colder environment (the outdoor air) to a warmer environment (the heated space).
The compressor increases the temperature and pressure of the refrigerant gas, so the suction line at the compressor will be warm to the touch.