Error code reference

Carrier Hvac Error Code 26

Invalid heater size

Invalid heater size — heater identifier resistor (IDR) value read is invalid for the combination of indoor and outdoor components installed.

First step from the service manual

Check wiring harness connections to be sure they are secure; disconnect wiring harness at fan coil control heater header and check for resistance value greater than 5000 ohms.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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Step-by-step tests with expected resistance, voltage, and continuity values
Wiring diagram references and connector pinouts from the OEM service manual
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Invalid heater size — heater identifier

From Service Manual 761204, p.16:

1.Check wiring harness connections to be sure they are secure; disconnect wiring harness at fan coil control heater header and check for resistance value greater than 5000 ohms.

2.Measure door lock assembly resistance across the PTC terminals. Expected: ~200 ohms cold, rising sharply once energized.

3.Inspect strike and latch alignment. A warped door or misaligned strike prevents the switch stack from closing in the correct sequence.

Part W10810403

Door lock assembly

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First step from the service manual

Get the full diagnostic procedure for 26.

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