Trane and American Standard Air Handler Error Codes

By Ray Bennett · Updated 2 October 2026 · 5 min read · Checked against the maker’s manual

Trane and American Standard Air Handler Error Codes

Short answer

On the TAM9 and TEM8 variable speed air handlers, a fault shows as ERR and a number on a Trane communicating thermostat, a number on the board's display, or a flashing red light. The ones you can act on: ERR 106 means an external switch, such as the float switch, is open, and ERR 157 a clogged condensate line. Frost protection stops the unit for 5 minutes to defrost the coil.

Trane and American Standard use the same TAM9 and TEM8 variable speed air handlers, and their control boards keep a list of faults with a number for each. Trane publishes that list in its Service Facts, the sheet written for the installer.

Most of the codes are for a technician. A few name something you can look at yourself, and this page starts with those. Trane’s own homeowner support says that for a numeric code such as Err 106.00, the next step is your HVAC dealer.

Before you start

What to carry: a torch and a pen. Ten minutes.

Gas or electric? Electric. The air handler runs the blower for a heat pump or air conditioner, and on 230 volts it can also carry electric heat strips.

Write the code down first. Trane says the boards store active and past faults, and report the last four after a power cycle. Note the number before you switch anything off.

Before you open anything. 230 volts inside. Trane’s own warning says only qualified people should install and service this equipment. Switch the power off at the breaker before a panel comes off.

The same code twice. A code that comes back after a reset is a fault still there. Trane’s homeowner support says to call your HVAC dealer for a numeric error code.

Where the code shows

Three places the same fault can show. The number on a Trane communicating thermostat is the alert code in Trane's table.

Check 1Free, five minutes

Find the number

On the thermostat. Trane’s communicating thermostats show ERR and a number, such as ERR 106. Trane’s table lists the same code for its TCONT900 and TZONE950 controls.

On the board. The TEM8 shows its fault number on a small display on the AFC control board. On the TAM9, Trane says every fault can be read from its display assembly.

On the lights. The TAM9’s EVC board flashes a red fault light, a blue unit light and a green status light, explained further down.

The codes you can act on

The Trane air handler codes that point at something an owner can check. The rest belong with a technician.

Check 2Free to a service call

Check the drain, the filter and the wires

ERR 106, or 13 on the TEM8’s display. Trane calls it an external shutdown: an input is open, and it names the external float switch or another device. Look for water in the drain pan: clearing the drain line.

ERR 157, or 11 on the red light. Trane says the condensate drain switch has been activated for 100 seconds and cooling is disabled. Its cause: a clogged condensate line, and a switch to clean.

Frost protection, 13 on the red light. Trane says the TAM9 stops everything for 5 minutes to let the indoor coil defrost. It lists low or incorrect airflow, a low refrigerant charge and sensor calibration, and calls it normal in cooling on a cool day: why a coil freezes.

ERR 91.02, or 3.2 on the TEM8. Trane says the heat or cool demand message was lost. Its TEM8 sheet says to check the thermostat wires: thermostat wiring.

Alert 90, or 3.3 on the TEM8. Too many communication errors. Trane names R and B at the thermostat swapped, and for the TEM8, an accessory, a UV light or electrical interference. Its test is to disconnect accessories and see if it returns to normal.

The lights on the board

Check 3

Read the lights

The blue unit light. Trane says one flash every four seconds is normal. Two flashes a second is a communication busy error, solid on means it cannot talk to the AFC board, and off means no power.

The green status light. On the AFC board, Trane says it stays on for 2 seconds after power up, then flashes once a second in normal running.

The EVC’s green flashes on a heat pump. One is cool mode with no call, two a first stage cooling call or defrost, three second stage cooling or defrost, four heat mode or the system switched off, five first stage heat and six second stage heat.

The red fault light. Off means no fault. A count means the code in Trane’s EVC table, such as 11 for the drain switch and 13 for frost protection.

The codes for a technician

Code	What Trane’s table says
ERR 114, or 1.1, 1.2, 2.1, 2.3, 2.4	The motor, or the PM module Trane pairs with it, is missing, wrong or not supported
ERR 123, or 6.1, 6.2	Electric heat configuration: a heat call the board was not set up for
ERR 155, 163, 164	The indoor electronic expansion valve, its motor or its control
ERR 156	High superheat: the system low on charge, or a restriction
ERR 159	Communication between the boards: the wire harness
ERR 161	An indoor coil temperature sensor open, shorted or unplugged
ERR 166	Low superheat: a stuck valve, a sensor, or a restricted line
ERR 171, or 2.2	Blower communication lost: the harness or the variable speed motor
ERR 91.03, or 3.1	Loss of Bit Master, a control fault: Trane says replace the AFC board
ERR 172	A stuck key on the display assembly
12 on the TEM8	Constant torque failure: Trane says replace the board

Clearing the history

Check 4

Clear it only once it is fixed

From the display. Trane says go to the Alert menu, then Alert History, then Clear History, and press Enter twice.

From the board. Trane’s other way is to hold the Unit Test button for 10 to 12 seconds, release it, wait 5 seconds, then cycle the 230 volt power to the unit.

Why wait. A cleared history is a lost clue. Leave it for the technician if the fault is still there: an air handler that is not working.

Questions people ask

What does ERR 106 mean on a Trane?

Trane calls it an external shutdown: an input on the air handler is open, such as the external float switch. Check the drain pan and the condensate line.

What is error 157 on a Trane?

A condensate overflow. Trane says the drain switch has been activated for 100 seconds, cooling is disabled, and the condensate line is clogged.

Why did my Trane air handler stop for 5 minutes?

That can be frost protection. Trane says the TAM9 stops everything for 5 minutes to defrost the indoor coil, which is normal in cooling on a cool day.

What does the blue light on my air handler mean?

One flash every four seconds is normal. Two a second is a communication busy error, solid means no link to the AFC board, and off means no power.

Are Trane and American Standard codes the same?

For these air handlers, yes. Both brands use the TAM9 and TEM8 model names, and Trane’s Service Facts sheet is the one supplied with the American Standard models.

Should I clear the error code?

Not until the fault is fixed. The history helps the technician. Trane’s homeowner support says to call your dealer for a numeric code.

Sources: Trane (Ingersoll Rand) Service Facts TAM9-SF-1A-EN for the TAM9 and TEM8-SF-1A-EN for the TEM8 variable speed air handlers, and Trane Home support "Error Codes - What to Do?"