Be sure that the power distribution box has sufficient power provided to it. Long cable runs can result in a voltage drop, which can be solved by using a heavy gauge wire. A failing relay often means the HVAC fan won't run or runs nonstop; relay faults are common and fixable. This guide on Hvac Fan Relay Troubleshooting breaks down causes, tests, and fixes in. Use a volt meter to measure voltage at the power supply and at the power distribution box. Check wires/DIN terminal clasps to. When your HVAC system stops blowing air or your furnace fan runs nonstop, the issue often points to a small but vital part: the HVAC fan relay. Second, you've got both aluminum and copper wire here. It covers electrical issues, control signals, refrigerant-related.
[PDF Version]