Electrical connections and wiring harness rules

What is going on

Before you touch any wiring on this furnace, read these rules. Line voltage and low voltage control wiring share the same cabinet, and mistakes can cause dangerous operation, shock or a failed control. The 115 V connection section continues past this page range, so use the full manual for the supply details. Take your time, and confirm power is truly off with a meter before reaching in.

Likely causes

• Power left connected during service, with multiple power sources present
• Unlabeled wires reconnected wrongly
• Unpolarized or ungrounded supply
• Replacement wire not rated for the heat
• Supply voltage, frequency or phase not matching the rating plate

Check in this order

1. Disconnect all electrical power before servicing or changing any wiring. Multiple power sources may be present, so verify with a meter.
2. Make sure wiring to the unit is polarized and grounded.
3. Label all wires before disconnecting them when servicing controls, since wiring errors can cause dangerous operation.
4. Verify proper operation after any servicing.
5. If any original harness wire is replaced, use wire rated at least 105 C and copper conductor only.
6. Check that supply voltage, frequency, and phase match the unit rating plate before making 115 V connections.
7. If unsure, call a licensed electrician or qualified technician.

More furnace guides

• Airflow lower than demanded, furnace runs on low stage when high stage is expected
• Alternate combustion air opening (upflow or horizontal)
• Alternate vent/flue location (upflow or horizontal left)
• Annual inspection checklist
• Auxiliary limit control (location and purpose)
• Auxiliary limit switch open (blower compartment)