Blower motor works on med high and high only

[ssobel80]

I replaced the resistor the other day I thought it was working but can't say for sure. Now I only have med high and high! Is there another cause of this or is the resistor bad

 

[Chikar]

The link will allow you to download the wiring diagram for the heater blower circuit in PDF format.

http://dl.dropbox.com/u/45028330/air-conditioning-manual-a-c-circuit-1-of-1.pdf

Assuming the replacement resistor is in fact good the next most likely cause is the fan speed switch itself or the wiring between the resistor connector and the switch.

As a test, unplug the connector at the resistor, put the speed switch to medium low and the selector switch to Floor.

With an ohmeter check for continuity from the pin attached to the light green with white stripe wire to ground. Ideally it should read zero ohms meaning the circuit is OK. It's probably OK if it reads up to 5 ohms or so but much more resistance than that would be a problem. Also check from the pin connected to the black wire to ground. Ideally 0 ohms again.

Note that when Hi is selected the High Speed Blower Relay energizes and power flows from +12 through the blower motor, the relay and then to ground, completing the circuit. The blower resistor isn't used at all.

When MedHi is selected power flows through the motor, the first resistor in the blower resistor, through the switch, to ground completing the circuit.

MedLow is the same except for power passing through the first two resistors in the blower resistor pack.

When Lo is selected power passes through all three resistors in the blower resistor pack bypassing the speed selector switch completely.

If the continuity tests from the blower resistor connector through the speed selector switch pass then I'd be really suspicious of the blower motor resistor.

 

[PLANENUTS100]

Had exactly the same problem. Turned out it was he pigtail to the resistor pack. Got a replacement from Oreilly, wired it in and problem solved!

 

[ssobel80]

Thanks! I will check it out this morning!! If the resistor is bad I would assume that there is another problem causing the new resistor to blow. Any ideas what I should check (and how to check it) before I replace the replacement resistor.

 

[Chikar]

Just keep in mind the new resistor may not be blown.

The continuity tests of the wiring are key and should be done first before just replacing the resistor again. You could have a faulty speed selector switch or a bad function selector switch (Floor, Panel, etc.). A bad function selector switch is far less likely but is possible. Or you may just have a wiring problem. A short somewhere from a frayed wire, an actual break in the wires, that sort of thing.

A quick test of the resistor pack would be to do a resistance test with an ohmeter. The connector will have an Orange wire with a white stripe. You'll need to determine which pin on the resistor pack corresponds to that wire. Connect one lead of your ohmeter to that pin. There will also be a black wire on the connector so determine which pin on the resistor pack corresponds to that wire and connect the other wire from the ohmeter to that pin.

The resistance between those two points should be 3.03 ohms +/- 10%. If there's no resistance (continuity) between those two points the resistor is bad.

That would be an unusual situation though. Generally having one resistor in the blower resistor pack go bad (which would be the case judging from your description of the problem) is very, very unlikely.

We don't yet know the resistor is actually bad. As PLANENUTS100 described it was the pigtail to the connector that was bad. I'm assuming he meant the actual connector that plugs into the resistor pack. Which indicates the problem was in the wiring or connector, not the resistor.

The continuity tests will pin it down.

Hope this helps you figure it out.

 

[ssobel80]

So I finally got the chance to check this out today. I go out turn the blower to med low and it works!!! Everything is working perfect now! I am gonna have to assume that there is a bad connection or other wiring problem. Thank you for your help

 

[PLANENUTS100]

Glad things are working again. Sounds like a bad connection. Try coating all the connectors with diaelectric grease, especially the pigtail to the resistor pack.