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Check voltage with AC on Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Wed, 10 Jun 2009 20:35:43 In Reply to: ac on "lo" dragging down voltage below 12, randomly..., aaron, Tue, 9 Jun 2009 21:34:47 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The EDU doesn't read voltage at the battery - it reads based on the voltage bus it is connected to, and the local ground. So the EDU reading is greatly influenced by changes in current loads. So the EDU might read 0.2 low normally, but with the AC on, it might read lower.
The voltage will jump around as the electrical load changes. The AC compressor cuts in and out normally - setting the temp to LO doesn't change that. So when the compressor clutch has cut in, you will pull a lot of current and the voltage will normally drop a bit. The voltage will spring back up when the clutch releases. As the others have noted, the VR is temperature compensated, so the hotter it is under the hood, the lower the alternator output voltage will be, so it's normal to see the voltage drop down as things heat up.
Seeing a voltage below 13 when the engine is above 2000 rpm is worrisome; that's why it would be good to verify that the EDU reads correctly when the AC clutch is engaged and the underhood temperatures are warm. But you could be just looking a poor grounding around the EDU, nothing more.
posted by 75.25.4...
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