How to check fan blower switch I need diagram of the switch

Did you check for voltage and ground at the blower motor connector? You may be way ahead of me? Different speeds are controlled on blower motor ground circuit. In the diagram, the top wire at blower motor is voltage and the bottom wire is ground. The diagram may not be what you wanted? Brown is voltage, orange is ground at blower motor. Maybe you can hit control and plus on your key pad to enlarge diagram.

First check the fuse,if ok. Check if you still get power to the blower motor, on the plug, if so. you need to replace the blower motor and resistor. if not check power supply to blower switch,and power after the switch, if you turn switch on and off.

Don't know where you got your info . The heater blower motor electrical B+ power comes from Fuse F 64 a 40 amp fuse . This goes right to the blower motor on the green with orange stripe wire , The black with red stripe wire goes to the switch for high speed . There is Splice 24 that ties into the black with red stripe wire. The splice 24 turns into a black with orange stripe wire . An this wire goes to the blower motor resistor . All the switch does is route the B+ voltage through the different resistors to ground .

Thermal resistor "usually" stops working is because of faulty fan speed switch ???? Totally not true , resistor assemblies fail because of the heat associated with dropping voltage across the resistors , That is why they put the resistor assembly in the air box . Air blows over to cool the resistors . The switch is nothing more then a way to direct different speeds to ground .

Rather then listening to other people ,why not learn the right way to test electrical circuits .
Electric Testing Techniques You Need to Know

Do you know what a wiring diagram is ?
http://www.bbbind.com/free_tsb.html Enter vehicle info . Under system click on HVAC , under subsystem click on heater . Click the search button , then on the link . Use a volt meter an test , don't guess !

You need a blower motor resistor. 1986-1992 Oldsmobile Cutlass Ciera Blower Motor Resistor - 4-Seasons
zoom Be the first to write a review.

Part #: FS20072
Mfr #: 20072

This is a blower motor not working tip I posted a little while back.

Blower motor problems are a pretty common topic. This is a basic guide on how to diagnose the problem and will work for most vehicles.

The diagram is generic and loosely based on GM's setup and more specifically a Silverado. Most manufacturers have a similar setup and the only major differences would be a ground side control (instead of the switch supplying power to the resistor it would be grounding the power from the resistor if this is the case you test light would need to be connected to power to test the switch) and late model Chrysler minivans (they use a module that looks for a difference in a/c voltage from the switch)

If the blower works on high only than likely the resistor assembly is the culprit since power to the blower essentially bypasses all of the resistors and/or the resistor assembly entirely. The reason why none off the other speeds will work is that the resistor or the circuit for the speed four setting has burned out. The lower the setting the more resistance you need to drop the voltage to the blower. The first speed setting requires all four resistors to drop the voltage enough to turn the blower at its slowest speed. Speed 2 needs to turn the blower a little faster so it uses three resistors. Speed 3 uses two resistors and speed 4 uses one.

In some cases the fan will work on high and speed setting 4. The likely cause for this is the speed 3 resistor or circuit has burned out. Speed 4 still works because it doesn't use the lower speeds resistors to control the speed of the blower. If the speed 2 resistor burns out than speed 1 and 2 will not work but 3, 4 and high will continue to work. If the speed 1 resistor burns out than speeds 2, 3, 4, and high will continue to work.

This leads us to how do we know if its the resistor or the switch or the blower. If the blower works on high than we know the blower works. That leaves us with either the switch or the resistor assembly (there are many other possibilities) which can be easily tested with a test light (or a voltmeter if you choose) The first thing to do is locate the resistor assemble. They can be behind the glove box, under the dash close to the blower motor or under the hood, again usually close to the blower motor. It will typically have 5 to six wires going to it. We'll start by unplugging the connector, turning the key on and connecting your test light to ground.

1.Turn the switch to high and backprobe all the wires. Two of them should illuminate the test light. In the diagram below this would be wire E & F. If you don't have a diagram then hold the test light on one of the two wires and move the switch to another speed setting. the wire that continuously illuminates the test light regardless of the switch position will be the constant power for high blower speed and will not need to be rechecked in the following steps.

2. Turn the switch to the next lowest setting. Backprobe the remaining wires to see if one of them illuminates the test light. Repeat until you have checked all of the speed settings.

3. If the test light has illuminated a different wire for each setting then we can reasonably assume that the switch is functioning as intended and the source of the problem is the blower resistor.

If you find one or more settings (but not all the settings) on the switch that does not illuminate the test light on any wire than we can reasonably assume that the switch has failed.

There are a few other things that can cause blower motors not to work as intended. The switch or the resistor assembly are the two most common problems.



I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

You'll have to find the correct wiring diagram in order to trace down the fault in your system.. Once you obtain the wiring diagram you'll be able to see what else beside wire is between the #4 speed setting and the blower motor. My guess is you might find a high speed fan relay is triggered from the #4 fan switch setting, applying full battery voltage to the blower motor. If locating the appropriate diagram proves to be difficult you can try looking around the underhood and passenger compartment fuse panel to find a relay. Keep in mind not all relays are always in fuse boxes which makes the diagram important.

Two possible areas I would check using an ohm meter. First is the blower resistor which is usually located by the blower motor and looks like a cement rectangle or a ceramic tube with wires attached to it. The resistor should have very low resistance but should not read open from the common lead to the other terminals. If it tests good test the continuity of the fan switch. Some cars have a fuse for the high and low blower speeds so you can check your fuse diagram and look for two blower or fan fuses. Good Luck.

what voltage reading do you get at the motor in respect to a known earth? Im thinking you have lost the motor earth.

Hi Nomad, this is a common problem with the Rodeo, rain water drains down into the fan blower which shorts it, causes rust, seizes etc, which then burns out the fan resistor pack. I had my one replaced but did not replace the blower as it seemed to be ok after I unseized it, the new resistor pack lasted a week, Probably should have replaced the blower to. I now have wired it straight, so I have full fan or no fan. I have also drive a 6mm hole in the botom of the fan where there looks like a channel to allow any water to drain out, I also sprayed CRC into it.