Customer bundle: auxiliary condensate switch wiring

What is going on

Aux alarm input on the GMVC96 family control. It's meant for a condensate switch, and compatible CO2 sensors or fire alarms can use it too. Switch is normally closed. Opens on high water, control shuts the furnace down.

Likely causes

• Condensate switch open because the drain is backed up
• Switch wired to the wrong terminal or wire loose
• Switch itself failed open

Check in this order

1. Confirm the switch is landed on the Condensate terminal.
2. Confirm the switch is normally closed. It opens when the evaporator base pan water level is too high.
3. If the switch is open, check the condensate drain first. Look for a plugged line or trap.
4. Clear the blockage, let the pan drain, then see if the switch closes again.
5. With power off, check the switch for continuity by meter. Open with a dry pan means a bad switch.
6. Check the connections at the terminal for looseness.

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)