AC Unit Blinking Yellow Light: Comfort Alert Flash Codes

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the maker’s manual

AC Unit Blinking Yellow Light: Comfort Alert Flash Codes

Short answer

A yellow light blinking in the outdoor unit is usually a Copeland Comfort Alert module counting out a code. 1 flash is long run time, 2 a pressure trip, 3 short cycling, 4 a locked rotor, 5 an open circuit, 8 a welded contactor and 9 low control voltage. A red TRIP light means the thermostat is calling but the compressor is not running.

Many air conditioners and heat pumps with a Copeland Scroll compressor carry a small module in the outdoor unit’s electrical box, next to the compressor contactor. It has three lights, and the yellow one counts out a code when it sees a problem.

Everything on this page comes from Copeland’s own Comfort Alert user’s manual, 2006ECT-54 R3, for single phase systems, the kind on most homes. Some makers build their own control board instead, so if your lights are labelled differently, the diagram inside your unit’s panel has the final word.

Before you start

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

Gas or electric? The outdoor unit is all electric, whether it is an air conditioner or a heat pump, and it does not matter what fuel the furnace indoors burns.

Count, pause, count again. Copeland says the yellow light flashes a number of times, pauses, and repeats. The number of flashes is the code.

The last code waits for you. Every time the module powers up, Copeland says it shows the last code from before the shutdown for one minute.

Look, do not reach in. The box holds full line voltage. Copeland’s manual warns of hazardous voltage inside the unit and says to disconnect power before servicing the module. If the lights can only be seen with the service panel off, look without touching anything, or leave the reading to a technician.

The module does not protect the system. Copeland says this version is a monitoring device only and cannot shut anything down. A code that keeps coming back is a fault still happening.

What the three lights mean

Green says it has power, yellow counts the code, red says the compressor should be running and is not. Yellow and red flashing together means low control voltage.

Check 1Free, two minutes

Read the lights

Green, POWER. Copeland says the module has voltage at its power connection.

Red, TRIP. The thermostat is calling for the compressor but the module sees no current to it. Copeland says it usually means the compressor’s own protector is open, or power is missing to the compressor.

Yellow, ALERT. Count the flashes between pauses and find the number in the table below.

Yellow and red flashing together. Copeland says the control circuit voltage is too low to operate.

Every flash code

Flashes	What Copeland says it means	Causes Copeland lists
1	Long run time, the compressor runs extremely long cycles	Low refrigerant, the indoor blower not running, a frozen indoor coil, a dirty outdoor coil
2	System pressure trip	High head pressure, a dirty or blocked outdoor coil, the outdoor fan not running
3	Short cycling, the compressor runs only briefly	An intermittent thermostat signal, a time delay relay or board
4	Locked rotor	A failed run capacitor, low line voltage, liquid in the compressor, seized bearings
5	Open circuit	The disconnect open, a breaker or fuse open, the contactor failed open
6	Open start circuit	A failed run capacitor, start wiring, the start winding
7	Open run circuit	Run wiring, the run winding
8	Welded contactor, the compressor always runs	The contactor failed closed
9	Low voltage, control circuit under 17 volts	An overloaded transformer, low line voltage
Red TRIP	Thermostat calling, compressor not running	Protector open, the disconnect, a breaker, a broken wire, the contactor

The checks that are yours

Four codes point first at things you can check from outside the box: the filter, the coil, the fan and the power.

Check 2Free, twenty minutes

Work the owner checks

1 flash, long run time. Copeland’s list includes the return air filter, blocked registers, an excessively low thermostat setting and a frozen indoor coil. Change the filter and look for ice on the copper lines: why an air conditioner freezes up.

Is the indoor fan running? Also under 1 flash, Copeland names the indoor blower not running. With the system cooling, air should come from the registers.

2 flashes, pressure trip. Copeland names a dirty, blocked or damaged outdoor coil and an outdoor fan that is not running. Clear leaves and rinse the coil gently: how to rinse an outdoor coil without bending the fins.

2 flashes and a still fan. Copeland points at the fan’s capacitor, wiring and motor: why the outdoor fan will not spin.

5 flashes or the red TRIP light. Copeland’s first causes are the outdoor unit’s disconnect open and a breaker or fuse open. Check the disconnect beside the unit is in and switched on, and the breaker in the panel.

8 flashes, it never stops. Copeland says the contactor has failed closed and the compressor always runs. Switch it off at the disconnect: what a stuck contactor is and what it costs.

Resetting a code

Check 3Free, five minutes

Clear it, then watch

By hand. Copeland says to cycle the power to the module off and on. After it powers back up, the last code flashes for 60 seconds before clearing.

By itself. The module keeps watching after an alert, and Copeland says the code turns off on its own if conditions return to normal.

If it comes back. The fault is still there. Note the flash count and whether the red light was on, and give both to the technician.

When it needs a technician

Check 4

Know when to stop

4 and 6 flashes. Copeland lists a failed run capacitor first for both. It is a common, cheap part, but it stores a charge after the power is off: what a failed capacitor looks like.

1 flash with a clean filter and a running fan. Low refrigerant, a faulty metering device or a blocked filter drier. That is sealed system work.

2 flashes with a clean coil and a running fan. Copeland lists an overcharged system and air or other gases in the refrigerant.

5, 6 and 7 flashes that are not the power. A contactor, the compressor wiring or its windings, measured with a meter.

9 flashes. An overloaded control transformer or low line voltage. Copeland says to contact the utility if the voltage at the disconnect is low.

Questions people ask

Why is there a yellow light blinking on my outside AC unit?

On many units it is a Copeland Comfort Alert module flashing a code. Count the flashes between pauses: 1 is long run time, 2 a pressure trip, 5 an open circuit, 8 a welded contactor.

What does a red light on the outside AC unit mean?

On a Comfort Alert module, a red TRIP light means the thermostat is calling for cooling but the compressor is not running. Copeland lists the compressor’s protector, the disconnect, a breaker, a broken wire and the contactor.

What does 6 flashes mean?

An open start circuit: current only in the run circuit. Copeland lists a failed run capacitor first, then the start wiring and the compressor’s start winding.

How do I reset Comfort Alert?

Turn the power to the module off and back on. The last code flashes for 60 seconds after it powers up. If the conditions return to normal, it also clears on its own.

Does the light mean my compressor is dead?

Not necessarily. Many of Copeland’s listed causes are outside the compressor: the filter, the coil, the fan, the capacitor, the contactor or the power. Only a few point at the windings or bearings.

Sources: Copeland (Emerson Climate Technologies) Comfort Alert user's manual 2006ECT-54 R3, single phase systems