American Standard Communication Error with Communicating Thermostat

Error code 19: Furnace fan runs but there is no heat; the thermostat appears to be calling.

Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Loose ABCD communication bus wiring, incorrect polarity on communicating terminals, faulty American Standard communicating thermostat, damaged communication cable.

How to Fix / Troubleshooting

Safety: Turn off power before adjusting thermostat wiring.

Error 19 is common on communicating American Standard systems.

Check ABCD wiring:
- Verify that A, B, C, and D terminals on the furnace match exactly with the thermostat.
- Ensure all connections are tight and color-coded consistently.
Inspect the cable:
- Look for staples through the cable or sharp bends.
Reset the system:
- Power down the furnace and thermostat for 5 minutes, then restore.
If communication errors persist, the thermostat or control board may need replacement by a professional.

Repair Difficulty

Hard 4/5

Required Part

Communicating Thermostat

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