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Old 03-31-2015, 09:15 PM
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Join Date: Mar 2015
Posts: 2
Diagnosing W124 Climate Control Fault

Here is the issue: 1995 W124 E320, go to turn on heat, nothing. No servos for blend doors, no AC, no fan, nothing, on any setting. Ribbon fuse R15 is fine. Pulled and checked fan motor, works as should. Connections to motor seem fine. Getting solid 12V to red wire at X64 plug on firewall by the brake booster with ignition on, using black in same plug as the ground, however no voltage to Yellow signal wire, on any CCU setting. Replace CCU with 2x known good units, still nothing to Y wire. My understanding is that the voltage to the yellow signal wire that is a "trigger" to the voltage regulator under the fan should be between around 2v at low and 9v at high. I have nothing. What is the next step? (It seems that around the same time this issue cropped up the accelerator kick down stopped working, and to get it to kick down I have to manually shift it into 2 to get passing speed...any connection?!)

Thoughts? At wits end.....! Cheers.
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Old 04-01-2015, 12:48 AM
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Join Date: Oct 2004
Posts: 2,886
Sounds like a fuse problem. Get in the fusebox and check them all closely. They can look good while being bad so use your fingers and get tactile with them.
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Old 04-01-2015, 09:00 AM
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Join Date: Mar 2007
Location: Hampton Roads, Virginia
Posts: 3,306
If the key switch is sloppy, you can overshoot the contact.

Try slowly moving the key back and forth in the #2 position to see if power comes on.

Sounds like a power supply issue, if not the switch than start checking fuses.

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