Ford blower motor resistor problems remain the most common solution to interior fan malfunctions on Ford cars and trucks. With that said, failed blower resistor assemblies don't solve all of the possible failures. This is why at the bottom of the article we include a 2008 F150 blower motor wire diagram.
The interior fan is powered through two separate fuses and a blower motor relay. They control the HVAC circuit with a switch. On the automatic temperature control system they further complicate the system by using a module. Malfunction of these components can cause different symptoms and that's where we’ll start.
First we'll cover the most common symptoms associated with a bad Ford blower motor resistor. Next, we cover the different parts used on the Ford climate control system found on the fancier Lariat and Eddie Bauer edition vehicles. For Ford cars and trucks without ATC (Automatic Temperature Control) systems diagnosis becomes simpler. In addition, the replacement parts are also less expensive.
Before we move on I want to make one more important point. Whether you have a blower motor problem on a 2009 Ford escape, 2004 Ford F150 pickup truck or even an Expedition or Mercury mariner these blower motor control systems use the same parts. In addition, the wiring diagrams and the circuit operation also remain very much alike. However, the Ford Fusion blower motor resistor is a completely different animal.
The thin card type Ford blower motor resistor is the most common part used for the interior fan speed control. It fits almost all of the truck and sport utility vehicles like the Ford Escape, Expedition, Explorer and Lincoln Navigator from 1999 through 2012.
I'm also pretty sure this is the same part used in the Ford Crown Victoria. When this resistor module fails drivers often complain about losing individual blower motor speeds. Sometimes you will only have low and high speed settings. However, the most common complaint when this part fails is that only the high speed setting functions.
If you look at the wiring diagram for the Ford F150 below, you'll see that the high speed setting bypasses the resistor assembly completely. I'll go one step further and say that if you're blower motor works on high and you have the card type Ford blower motor resistor, no further diagnosis is required.
With the low cost of the replacement part and the high failure rate, I'll just go ahead and replace it. It would be nice if when you remove the old resistor module that you'd see the damage. Unfortunately, the part fails internally and often leaves no outward sign of malfunction.
With that said, sometimes you’ll be able to smell some electrical burning or melting odor. We have one more important point to make about this Ford blower motor electrical problem. The four wire connector that plugs into the resistor module needs a thorough inspection.
Not only can the connector melt, but the heat can distort the terminals. If you observe any damage or discoloration of the terminal, you should always replace the connector. You can purchase these pigtail electrical connectors separately.
When you have blower motor speed control problems on a Ford with ATC the failure can still point to a failed resistor module. However, the part looks a lot different than the card type module discussed above.
It's important to verify the correct replacement part as variations exist throughout the different years and models. The Ford blower motor resistor deployed on the automatic temperature control systems is larger and has aluminum heat sinks incorporated into the design.
These cooling fins channel heat away from the internal electrical components. Since the resistor fits into the heater case they direct air created by the spinning fan, called the squirrel cage, across the heat sink fins.
This is an efficient way of cooling down the entire module assembly. Unfortunately, failure of the component still remains possible despite the best efforts of cooling the parts down.
In fact, overheating of the resistor becomes more likely to damage the electrical connector that plugs into the assembly. For this reason they now sell replacement parts that include the replacement connector referred to as a pigtail.
As you can see from the image, they also include heat shrink connectors. These butt style connectors crimp the wires together. Then you heat the plastic parts and they shrink to form a weather tight seal around the electrical wire repair. When you buy replacement blower motor resistor modules from the Ford dealer they are much more expensive and they sell the pigtail connectors separately.
Before we get into other Ford blower motor speed control problems let's talk about what happens when the fan motor doesn't work at all. In many cases when this situation occurs, you have a blown fuse. As you can see from the wiring diagram below, there are two fuses protecting the circuit.
Both of these need to be intact for the blower motor to operate properly. The question becomes, why did the fuse burn open? It's possible for the electrical failure of the blower motor resistor to take out one or both of these fuses as it melts. Although this isn’t as common, the chances of this happening increase if you have a melted electrical connector.
With that said, if the blower motor doesn't work at all it's also common to find a defective blower motor relay. Note that the interior fan circuit contains two relays in the same way that it contains two fuses. You can verify this in the Ford F150 blower motor diagram below.
If the blower motor doesn't work at all, you probably have a defective relay. However, if the only speed the fan is missing is the high setting than the likely cause of the problem becomes the high-speed relay. Remember that it’s possible for the blower motor to fail itself.
Although the motor is one of the most reliable components of the system it won’t last forever. Now let’s cover the least likely cause of problems with the interior fan speed settings. Both the automatic temperature control and the standard air-conditioning systems use switches on the control panel.
Although switch failure remains uncommon compared to all the other possibilities, it still remains possible for the switch to fail. Now here’s the Ford blower motor wiring diagram. You can use to get an idea of how the circuit operates on vehicles without automatic climate control.