The System Runs but the Blower Doesn't: Working the Split

The condenser is running. The thermostat is calling. The indoor blower is doing nothing. That specific combination is more useful than a general no-blower complaint, because it tells you the low voltage circuit is alive and the equipment is trying. Something between the call and the motor is not completing.

This is the split-the-circuit version. For the broader symptom list, start at blower motor troubleshooting.

What the symptom already tells you

If the outdoor unit runs on a cooling call, then the thermostat, the low voltage supply and the cooling side of the board are all doing their job. That rules out a surprising amount of the usual list before you open a meter.

What remains sits in three places: the fan command from the board, the power feed to the motor, or the motor itself. Work them in that order, because two of the three are cheap to check and one of them is the expensive assumption.

The fan command

On a cooling call the board should energize the blower after its programmed delay. Wait out the delay before deciding anything, since a lot of boards hold the blower for a fixed period and techs call the fault during the wait.

Then check whether the board is actually commanding the motor. On a constant torque X13 that means 24 volts on one tap input. If the command is present and the motor is dead, you have moved the fault downstream. If the command is missing, the motor is fine and the fault is the board, the thermostat wiring, or a safety that opened.

The safeties nobody checks first

Several devices break the blower circuit while leaving cooling alive, depending on the equipment:

• A float switch or condensate overflow switch, which on some wiring schemes kills only part of the system.
• A blower door interlock that is not fully seated. This one is free to check and embarrassing to miss.
• A limit or rollout on furnace applications, which will keep the blower behavior odd rather than absent.

Cycle the door switch by hand before you go further. It costs nothing and it is a real percentage of these calls.

Power at the motor

Line voltage and ground at the power connector, measured at the connector rather than assumed from the breaker. An ECM with no line voltage is a dead motor that will test perfectly on the bench.

If line voltage is present, the command is present, and the motor still does nothing, then the motor is finally a suspect. Confirm it properly with the ECM diagnostic sequence or with a meter following how to test a blower motor with a multimeter.

The mechanical answer

Before you order anything, put a hand on the wheel with the power off. A wheel that will not turn freely means the motor was fighting a seized assembly, and a new motor dropped onto the same seized wheel fails the same way. Getting it apart is covered in getting a seized blower wheel off the shaft.

Look for the bearing that has been screaming for a season, the wheel packed solid with dust, or the shaft that is scored. Those explain the failure. A motor that simply died with no story usually did not simply die.

When it is the motor

Read the plate before you disconnect anything, using how to read a nameplate, and note the rotation. Then put the part number or the equipment model into the ECM motor cross reference. It returns the remanufactured OEM-spec motor, programmed, in stock, with the price on screen and a two year warranty.

Questions techs ask

Cooling runs but the blower is dead. Is it always the motor?

No, and it is often not. The command from the board, an open safety and the power feed all produce exactly this symptom, and all three are faster to check than a motor swap.

How long should I wait for the blower delay?

Long enough to be sure. Check the delay for that equipment rather than assuming, since fixed delays of a minute or more are common.

The motor hums but does not spin. What now?

Kill power and check the wheel by hand. A hum with no rotation frequently means the assembly is mechanically locked rather than electrically dead.

Can I bench test the motor out of the unit?

Only with the correct power and control connections for that motor. Applying the wrong voltage to a control input is a fast way to destroy a motor that was working.