Crazy multimeter reading on WJ blower - can anyone explain? - JeepForum.com
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post #1 of 7 Old 09-30-2019, 10:47 AM Thread Starter
AVR2
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Crazy multimeter reading on WJ blower - can anyone explain?

The blower isn't working on my 2002 WJ with the premium AZC climate control. It uses a blower motor controller module rather than a resistor block, and I suspect it's the controller module that's the problem, but I'm trying to diagnose properly rather than just change parts.

The motor controller module plugs into the blower with a 2-pin connector, one pin indicated as "motor supply" and the other as "high driver":



I hooked up my multimeter to the motor supply pin and a chassis ground, and I saw that I'm getting 12V with the climate control head unit switched on and 0V with it switched off.

However, when I measure across *both* pins of the connector (using "high driver" as the ground), I'm seeing 230V - and that's with the Jeep battery disconnected.

How the hell is that happening?

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post #2 of 7 Old 09-30-2019, 10:51 AM
Kruzin
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Usually when you see something like that, you just didn't notice the scale it's using. My guess is it's showing you 230mV not 230V
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post #3 of 7 Old 09-30-2019, 11:54 AM
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Quote:
Originally Posted by Kruzin View Post
Usually when you see something like that, you just didn't notice the scale it's using. My guess is it's showing you 230mV not 230V
Hence the reason I don't like autoranging.

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post #4 of 7 Old 10-01-2019, 06:04 AM Thread Starter
AVR2
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Quote:
Originally Posted by Kruzin View Post
Usually when you see something like that, you just didn't notice the scale it's using. My guess is it's showing you 230mV not 230V
I did not think of that

I was expecting to see 0V since the battery negative cable was disconnected. Is it normal to see very small voltages with the battery unhooked?
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post #5 of 7 Old 10-01-2019, 03:58 PM
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Could be picking up residual voltage from a capacitor.

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post #6 of 7 Old 10-02-2019, 05:25 AM
V8GCZJ
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Check voltage of the two wires going to the motor with them hooked up! Also did you check the motor itself, Is it working?
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post #7 of 7 Old 10-02-2019, 01:54 PM
Jerry Bransford
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You're measuring on the side that gets grounded when the fan is turned on. It will show 12v through the motor coil coming from the other terminal until the switch grounds that side and turns the motor on.

When you have a choice, buy American made.
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