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Blower Motor Diagnostics - No heat, no cold, no anything

Blower motor

About a year ago, we did a feature on heater core issues, when your blower fan is working fine, but you're not getting hot air. In that article, which you can read here, a follow-up was promised for diagnosing blower fan issues. It's come to our attention that we failed to do that follow up. So we're doing it now.

In our forums, user tjflemming75 had a problem with a 2003 Kia Rio whose blower motor is no longer working. A few issues surrounding the air conditioner light were mentioned, but can probably be explained by switch settings. On most cars, if the defrost is turned on, the A/C is activated automatically in order to "dry" the air (pull moisture from it) to increase its ability to pull moisture from the windows and speed up the defrost process.

In any case, a simple diagnostic of the blower fan and its circuit will likely solve tj's issues. In the forum, mechanics Jerryh20 and Big Block 409 chimed in with answers that we'll use as a base line for our explanation of blower motor diagnostics.

The fan that blows air into the cabin is commonly called a "blower motor." It's usually just a variable-speed electric motor with a fan mounted to its shaft. It's usually located on the passenger's side firewall, though it may be located elsewhere on some models.

To begin diagnostics, start with the easy stuff first and then move to the more difficult tasks.

First, locate the blower motor and the wires that connect to it. Most likely there will be a two- or three-wire harness that plugs into the motor. It should be possible to disconnect that plug/harness and using either a similar plug or wires carefully molded to avoid touching one another, "plug" a new set of wires into the motor and run them to the battery terminals. If the fan operates when power from the battery is given to it, then your fan is likely working fine and your problem is located in the circuit instead.

Reconnect the wiring harness to the fan, turn the ignition switch to "on" (don't start the vehicle, just have it in the "accessories on" position) and turn on the fan switch to activate the blower motor. Try jiggling the wiring harness leading from the blower. If the fan comes on occasionally when the wires are jiggled, you have a loose connection in the harness. Trace down to that connection, starting at the plug on the fan and working back. Otherwise, proceed with our list.

Next, shut off the car and check all of the fuses in the engine compartment and passenger's compartment that relate to the heater, air conditioning, and blower motor. They're likely on two or three separate circuits with their own fuses. The blower motor most likely has its own fuse in the engine's control box. If all of those fuses are OK or if replacing any iffy ones does not solve the problem, keep digging.

Disconnect the battery cables and hang or tie them where they will not ground or touch one another. Using a multi-tool, check the circuit from plug to relay/fuse all the way from the fan to the controls on the dashboard. This will take some work, but you're likely going to find an improper ground or a loose/lost connection. Repair the problem and reconnect the battery cables to test the fan again.

Most blower motor problems are not broken motors but are instead bad fuses or loose connections. Sometimes, a bad switch on the dash can also be the problem.