Trane / American Standard Error 156: High Superheat Error (Meaning, Causes, Fixes)

What the code means

Superheat is how many degrees the refrigerant vapor is heated above its boiling point by the time it leaves the coil; too much superheat means the coil is being starved of refrigerant. Trane's System Alert Guide lists two versions. ERR.156.00, High Indoor Superheat Error, means superheat above 30 degrees was detected by the indoor unit for 5 consecutive cooling cycles, and system operation is allowed. ERR.156.01, High Superheat Error, means superheat above 50 degrees was detected by the outdoor unit for more than 20 minutes in cooling or heating mode. Trane's alert code table for its communicating controls (CL2 codes) shows 156.00 as a Major alert displayed as SYSTEM1 ERR with the same 30-degree, 5-cycle rule, and 156.01 as a Normal alert displayed as LOW CHARGE, triggered by superheat of 35 degrees or more for more than 60 minutes. The two Trane documents give different thresholds for 156.01, so the exact numbers depend on your equipment and control version. Related alerts: 155 is an EEV motor fault, and 164 covers the indoor EEV stuck at its minimum or open position.

Likely causes

• System low on refrigerant charge, usually from a leak (Trane lists this first for both 156.00 and 156.01)
• A restricted liquid line or a clogged filter drier
• Indoor EEV (electronic expansion valve) motor not seated properly on the valve, or the wrong EEV for the unit
• Indoor coil temperature or gas temperature sensor out of range
• Outdoor suction temperature sensor out of calibration, mounted in the wrong place, loose or uninsulated (for 156.01)

Safe DIY checks

1. Write down the exact alert (156.00 or 156.01) and whether the system was cooling or heating; the technician will want both.
2. Check how the system is performing. If it still cools or heats normally, 156.00 lets it keep running, but schedule service rather than clearing the alert and forgetting it.
3. Replace a dirty air filter and make sure registers and returns are open. This won't fix a charge problem, but it removes airflow as a variable before the technician arrives.
4. Look at the refrigerant lines at the outdoor unit. Note any oily spots, frost or ice on the lines or coil, or a hissing sound, and tell the technician.
5. If the alert returns or the house isn't reaching temperature, call for service. A system that is low on charge loses capacity and can overheat the compressor over time, and refrigerant work needs a licensed technician.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 180.02 Trane HVAC System 180.02
• 67.06 Trane HVAC System 67.06
• 106.00 Trane HVAC System 106.00
• 126.00 Trane HVAC System 126.00
• 166.00 Trane HVAC System 166.00

All Trane codes →

Sources

1. Trane System Alert Guide (Aug 2020): ERR.156.00 High Indoor Superheat Error (above 30 degrees from the indoor unit for 5 consecutive cooling cycles, system operation allowed; low charge, restricted liquid line or filter/drier, indoor EEV motor not seated, indoor coil or gas temperature sensor out of range); ERR.156.01 High Superheat Error (above 50 degrees at the outdoor unit for more than 20 minutes in cooling or heating; low charge, restriction, suction temperature sensor calibration, location, mounting and insulation)
2. Trane alert codes table (CL2 codes): CL2.156.00 Major, SYSTEM1 ERR, superheat above 30 degrees for 5 consecutive cooling cycles, system operation allowed, verify correct EEV valve; CL2.156.01 Normal, LOW CHARGE, superheat of 35 degrees or more for more than 60 minutes