2007 XLT Fan Speed Controller not working. Not Resistor or Switch

[manamee]

I have a 2007 XLT Explorer. My AC only works on fan settings 2 and 3 (1 and 4 basically turn off the air.) I've changed the blower motor resistor as well as the switch on the dashboard, neither of which solved the problem. 2 and 3 also work when I switch to any of the other settings on the right side knob: MAX and all of the mixes. 1 and 4 don't work in any mode.

What are my next troubleshooting steps? It seems the resistor and switch are the more common fixes, but as neither worked for me I need some more experienced minds to help figure this out.

 

[J_C]

That is an odd one. Are you 100% certain that both the setting 1 and setting 4, stopped working simultaneously?

IF we assume that both the new blower motor resistor and switch are good (which is worth checking with a multimeter), then the only thing I can think of is that you have two faults. One being the high speed blower relay (or a fouled socket contact for it or the wire itself to the dash speed switch), which prevents operating in highest speed, and the other fault preventing lowest speed mode being the wiring (or connector corrosion) between the blower motor resistor and the dash outlet selector (A/C Panel/Floor/Defrost) switch.

Seems like I have heard of that blower motor resistor connector becoming damaged from heat and/or water ingress corrosion so I'd definitely check that. All else fails, hunt down a wiring diagram and trace where power stops with a multimeter.

 

[manamee]

That is an odd one. Are you 100% certain that both the setting 1 and setting 4, stopped working simultaneously?

IF we assume that both the new blower motor resistor and switch are good (which is worth checking with a multimeter), then the only thing I can think of is that you have two faults. One being the high speed blower relay (or a fouled socket contact for it or the wire itself to the dash speed switch), which prevents operating in highest speed, and the other fault preventing lowest speed mode being the wiring (or connector corrosion) between the blower motor resistor and the dash outlet selector (A/C Panel/Floor/Defrost) switch.

Seems like I have heard of that blower motor resistor connector becoming damaged from heat and/or water ingress corrosion so I'd definitely check that. All else fails, hunt down a wiring diagram and trace where power stops with a multimeter.

Hey, thanks for taking the time to help me figure out what's wrong with my explorer!

I do not know if settings 1 and 4 stopped working at the same time. I bought this explorer used and this is the state they were in when I got it.

I see you guys talking a lot about using a multi-meter to track down various problems, but unfortunately I don't know what it is that you're doing with this multi-meter haha. I do have one, but I have a very rudimentary understanding of how to work it.

It seems like I have a few steps to take here.

1. Check blower motor resistor with multi-meter (and check connector while it's out)
2. Check switch with multimeter
3. Locate high speed blower relay and test with multi-meter?

Does this seem like a logical set of steps to take? I guess step one is really to learn how to use a multi-meter more proficiently

 

[J_C]

Yes, use multimeter to check the resistor, on the meter's ohms/resistance setting. Visually inspect connector contacts, check switch with multimeter on resistance setting for low resistance between each of the two contacts the switch should be connecting at each of the various speed settings.

Check the wiring point to point for continuity (and low resistance) between each two points in the circuit. The high speed blower relay, you could probably swap with another of same type relay already on the vehicle, just don't swap it with the other, main blower relay as the blower won't work at all if that one is bad or missing.

Unfortunately I don't have wiring diagrams or relay locations for your model year.