Electrostatic discharge (ESD) precautions

What is going on

The integrated control module is a circuit board with static-sensitive parts, and a charge you cannot feel can still damage it. Damage often does not show up right away. The board may fail weeks later and look like a mystery intermittent fault. The goal of these precautions is to bring the furnace, the control and your own body to the same electrostatic potential so no discharge goes through the board. This applies whether the furnace is installed or sitting on the bench, and whether you are replacing a control or just unplugging connectors.

Likely causes

• Walking across carpet or sliding on a seat before touching the board builds a charge
• Handling a new control before grounding yourself, straight out of its package
• Working on an ungrounded furnace or bench with the board lying on an insulating surface
• Shuffling feet while working in a dry basement or in winter, when static is worst

Check in this order

1. Disconnect all power to the furnace before touching the control or any wire on it, and confirm it is dead with a meter
2. Touch a clean, unpainted metal surface of the furnace away from the control to discharge your body. Paint and dirt block the contact
3. Keep the body grounded while servicing. Do not shuffle your feet or touch ungrounded objects, and repeat the grounding step if you do
4. Hold the board by its edges and avoid touching components or the solder side
5. Discharge your body to ground before taking a new control out of its container
6. Put the old board in the new board's packaging for return, not loose in the toolbag

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)