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Join Date: Nov 2000
Location: Toronto Ont. Canada
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a/c relay troubleshoot

should one be able to jump the terminals on the compressor relay? Providing 12 v to the central terminal engages the compressor clutch...but there isn't 12 from any of the pins under the relay...is the juice from the control unit? Confused

Old 05-15-2011, 06:32 PM
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The power goes from the fuse to the a/c control unit to the a/c relay.
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Old 05-16-2011, 05:10 AM
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Check for proper charge, the system might be low on charge causing the low pressure switch to open not passing 12V to the clutch.
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Old 05-16-2011, 11:57 AM
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There could be other problems too. What year is the car?
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Old 05-16-2011, 03:33 PM
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944 ac

It is an '85.5 944. I checked the control unit...seems ok...no matter what I do no juice at the clutch. Pressure switch is bridged. When the central pin of the relay is energized it sends power to the clutch...and th fuse is good.
Old 05-16-2011, 04:43 PM
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Do the later cars have an a/c amplifier? The early car does and it's the source that sends power to the compressor clutch.
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Old 05-16-2011, 05:13 PM
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From the relay power goes directly to the clutch. Are you getting power to the relay from the control unit?
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Old 05-17-2011, 05:04 AM
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a/c power

Hi,
There isn't any power at the relay...it doesn't trip when the switch is thrown and there isn't a hot to jump to the centre pin. The control unit has power...atleast everything else opperates
Old 05-17-2011, 08:32 AM
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I'm not savvy enough to load a picture, but if someone can load the schematic here in the form of a picture, I can show you where I'd suspect the problem is.
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Old 05-17-2011, 04:36 PM
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Hi,
Could you describe it to me ...the contol unit seems fine...just no 12 v at the relay.
Old 05-18-2011, 11:39 AM
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On the diagram in the FSM there is a power distribution block for most everything a/c. Right below it in the picture you'll find "Cooling Fan" next to it G10. I assume G10 is hot. Any way from what I traced, the control unit can be hot while the compressor and other related items are not.

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Old 05-18-2011, 02:49 PM
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