American Standard / Trane Error 180.02: Low Supply Voltage Fault (Meaning, Causes, Fixes)

What the code means

American Standard and Trane are sister brands, and their communicating variable-speed outdoor units (Trane's alert guide names model families such as 4TWV, 4TTV, 4A6V and 4A7V) share the same alert code list. In that list the 180 family is the compressor drive watching its incoming line voltage. Trane's System Alert Guide (August 2020) describes ERR.180.02 LOW SUPPLY VOLTAGE FAULT as: supply voltage is less than 175 VAC, with a 5 minute soft lockout. Its listed possible causes are a brown out or power flicker, with the advice to look for other alerts in the same time period, since 178.01 (DC bus voltage low) will often accompany it. The ComfortLink II alert table rates CL2.180.02 (LOW VOLT CO) as a Major alert. For context, 180.00 and 180.01 are derate alerts: below about 200 VAC, or under high load, the drive reduces compressor speed instead of stopping. Trane's table gives 187 to 253 VAC as the supply range to verify when the related 178.01 low DC bus alert appears. Several other drive alerts (181.11, 181.14 and 181.15) list a power interrupt as a cause and note that 180.02 will often accompany them.

Likely causes

• A brownout, power flicker or short outage from the utility. This is the cause Trane names first, and it often shows up in the alert history after a storm or on hot afternoons.
• Voltage sag inside the house: a loose or corroded connection at the breaker, outdoor disconnect or unit terminals, or undersized wiring that drops voltage when the compressor ramps up. Trane's guide doesn't name house wiring directly, but anything that lowers voltage at the unit below 175 VAC will trigger the alert.
• Heavy loads on the same service starting at the same moment (an electric range, dryer, water heater or well pump), which can pull the voltage down briefly. This is general electrical background, not a Trane-listed cause.
• Rarely, a drive problem. When the alert stays current and the measured supply voltage is normal, Trane points technicians to its drive diagnostics.

Safe DIY checks

1. Look at when it happens and write it down: one alert after a storm or power blip is normal, and the unit restarts on its own after the 5-minute lockout.
2. Check the thermostat's alert history for companion codes, especially 178.01 (DC bus voltage low) or 181.11, 181.14 and 181.15. Trane says these often appear together with 180.02 after a power interrupt.
3. Make sure the outdoor unit's breaker is fully on and not warm or discolored, and that the outdoor disconnect is fully seated. Don't open the disconnect box or panel to tighten anything with power on.
4. Notice whether lights dim when the outdoor unit starts or when big appliances turn on. Report that to an electrician or your utility; frequent dips point to a supply problem, not the heat pump or AC.
5. If neighbors had flickering power at the same time, call the utility and mention it. Low voltage from the street is their fix, not an HVAC repair.

Parts that commonly fix it

Always match the part number to your exact model.

Related codes

• 175.01 Trane HVAC System 175.01
• 67.06 Trane HVAC System 67.06
• 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), p. 37: ERR.180.00-180.03, including ERR.180.02 Low Supply Voltage Fault, supply voltage less than 175 VAC, 5 minute soft lockout, brown out or power flicker, 178.01 often accompanies; pp. 36-40: 178.01 and 181.11/181.14/181.15 power-interrupt notes (distributor-hosted copy)
2. Trane ComfortLink II alert codes table: CL2.180.02 Major, LOW VOLT CO, supply voltage less than 175 VAC; CL2.178.01 DC bus below 220 VDC, verify supply between 187 and 253 VAC (distributor-hosted copy)