American Standard / Trane Error 67.06: Suction Temperature Sensor Fault in Cooling (Meaning, Causes, Fixes)

What the code means

American Standard and Trane are sister brands, and their communicating systems share one alert list. The 67 family covers the outdoor unit's temperature sensors: 67.00 ambient, 67.01 coil, 67.02 liquid line, 67.03 external outdoor sensor, 67.04 and 67.05 compressor dome (cooling and heating), 67.06 and 67.07 suction temperature (cooling and heating), and 67.08 compressor dome sensor not attached. Trane's System Alert Guide (August 2020) describes ERR.067.06 SUCTION TEMPERATURE SENSOR FAULT COOLING as: suction temperature sensor is faulted in cooling mode. The ComfortLink II alert table lists it as CL2.067.06, SUCT T SENSE, Major. The suction sensor sits on the suction (larger, insulated) refrigerant line at the outdoor unit, and the control uses it, together with pressure readings, to work out superheat. Trane's guide notes that on outdoor software version 3.x and later, a faulted suction temperature sensor can put the system into limp mode in heating (175.00, compressor speed fixed to a constant value); the guide lists that for heating only, so in cooling expect the 67.06 alert itself. 67.07 is the same fault seen in heating mode.

Likely causes

• The suction temperature sensor is open or shorted. Trane's check is a resistance reading: zero or infinite resistance means the sensor or its leads have failed.
• The sensor reads out of range. Trane says to compare its resistance to the temperature/resistance chart in the unit's literature; a sensor that's drifted, loose on the pipe, or poorly insulated can read wrong.
• No output voltage from the control board to the sensor. Trane's guide says a reading between 3 and 5 VDC at the board with the sensor removed confirms good source voltage; the ComfortLink II table says 5 VDC should be measured with the sensor disconnected.
• Damaged or unplugged sensor wiring between the sensor and the outdoor control board, for example from rodents, string trimmers or a connector that worked loose. This follows from Trane's open-circuit and no-voltage checks rather than being a separately listed cause.

Safe DIY checks

1. Note whether the alert shows as current or only in history, and whether it says cooling (67.06) or heating (67.07). Write down any other alerts from the same time, such as other 67.xx sensor alerts or 175.00 limp mode.
2. Turn the system off at the thermostat, wait a few minutes and turn it back on. If the alert returns right away, the sensor or its wiring is the likely problem.
3. With power off at the outdoor disconnect, look along the insulated suction line near the outdoor unit for chewed, cut or crushed sensor wires or insulation that's been pulled away. Don't open the unit's control panel.
4. Keep the area around the outdoor unit clear so a technician can reach the service panel.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 175.01 Trane HVAC System 175.01
• 180.02 Trane HVAC System 180.02
• 106.00 Trane HVAC System 106.00
• 126.00 Trane HVAC System 126.00
• 156 Trane HVAC System 156

All Trane codes →

Sources

1. Trane System Alert Guide (Aug 2020), pp. 12-14: ERR.067.00-067.08 outdoor sensor faults, including ERR.067.06 Suction Temperature Sensor Fault Cooling (sensor open or shorted, zero or infinite resistance, out of range, compare to chart, no output voltage, 3-5 VDC with sensor removed); p. 33: ERR.175.00 limp mode from suction sensor fault in heating (distributor-hosted copy)
2. Trane ComfortLink II alert codes table: CL2.067.06 Major, SUCT T SENSE, suction temperature sensor faulted in cooling mode, 5 VDC with sensor disconnected (distributor-hosted copy)