Question

the electric back - up heating system on a heat pump should be
upstream of the indoor coil
downstream of the indoor coil
interlocked so that the electric heat will not be on when the heat pump is on
interlocked so that the electric heat must be on when the heat pump is on
wired so that only the heat pump will be on in the emergency heat situation

Explanation:

The electric back - up heating system and the heat pump are designed to work in a complementary way. To avoid inefficiencies and potential damage, they are interlocked so that they don't operate simultaneously. When the heat pump is functioning properly, the electric heat is not needed and should not be on.

Answer:

C. interlocked so that the electric heat will not be on when the heat pump is on