Why does heater fan only run on high? - 2002 Ford Taurus

A failed blower motor resistor can cause a heater fan run only on high, or not at all. If the motor is faulty, or replaced with a non-oem

You are talking about your blower fan for the air conditioner and heater right? More information will be needed to solve the problem.

When you say it barely changes speeds, does that mean it doesnt speed up, or doesnt slow down? By that I mean, is it "stuck" on low, or high?

Most blower fans run at different speeds through the use of a multi-stage resistor built into the fan switch circuit. Low speed is a high value resistor, medium speed is a low value one, and high speed is the fan running without any resistance.

If your fan is running on high and doesnt seem to want to run on lower speeds, the resistor pack may be failing. If the fan is running on low speed only, it may be that the fan itself is beginning to fail, or that the lubricant in it has gotten gummy.

if the problem is the fan only runs on high no matter were the fan control switch is then this sounds like the blower motor resistor is the problem.

I assume that you are talking about the heater fan?

Your heater FAN has at least 3 settings, and for our purposes we will assume low,med and high

Low and medium run through a resistor High is wired direct
Either your resistor is bad or your fan is
I know it seems wrong that the fan could be shot but it could be pulling so many amps that it won't work in any other mode than high
I just had this happen on one of my trucks
Start with the fan

replace the blower motor resistor located on the heater box were the blower motor is located the wiring to the blower may go to it. This is very easy to locate if you buy the part first.

probley the restor that gives the a/c heater fan motor its power for the low/ medeam speds has gone bad and onley letes it run on high speed because it gives the fan motor full battery voltage on high speed. it should be located in the heater box were the fan will blow air across it to cool it when it is in use GEORGE STIRBER DBA AUTO ENGINEERING

Check for a faulty heater fan relay.
Contacts may be sticking.

Your Heater Power control module is bad I just had the same problem you can find it right behind the glove box it is mounted in the heater duct very easy to fix 2 screws and it is out and cost is about 150.00 at the dealer it is a dealer only part.

When your heater only works on high it is usually
the resistor unit in the heater passage housing. Look for wires ( about 4or 5 wires ) attached to the
plastic heater housing under the dash. It should
have a screw or two holding it to the housing. Pull
it out and you will see several wire coils. If they are melted or broken then thats the problem. On any switch position except high the power goes through these resistors to slow the fan down. Good luck. Neil W.

Check or have checked the blower motor resistor. This is usually how they act.