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So yet another chapter unfolds in the A/C gremlin saga of my LS1 Chevy.


  • A/C compressor is relatively new (2 years old)
  • One of the belts is squeaking (not sure which one)
  • Recently performed a thermostat swap (the only reason why I mention this is because the thermostat housing is mounted directly above the compressor and a bit of coolant did spill on the compressor)


  • The alternator outputs ~14.5 V with the A/C off.
  • With the A/C on, the alternator outputs 10-12 V, the battery symbol lights up, and a 'Check Alternator' warning shows up on my display. After some time the steering goes hard as well, indicating loss of power steering. Cooling is abysmal.

My Thoughts

The symptoms appear to suggest that the compressor is inducing a parasitic draw on the engine (seized bearing, perhaps?), which surprises me since this is a two-belt setup (one for the A/C, one main).


  • Is it reasonable to expect that a seized compressor bearing would cause loss of tension in the main belt to the extent that alternator and power steering pump functionality is compromised?

  • Could there be some non-mechanical issue that explains this behavior (such as electrics)?

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Year, Make, Model? – Bob's sock puppet Jul 17 '14 at 14:03
How much does the engine RPM drop when the A/C comes on? Is the voltage drop with the fan blower on high, or just on the low side? – Pᴀᴜʟsᴛᴇʀ2 Jul 17 '14 at 14:17
could maybe be a short circle somewhere in A/C system. Check the Amperage at turning on/off the A/C. It can not be, that the alternator is not strong enough. – Watsche Jul 17 '14 at 14:34
@Larry, 2004 Chevrolet Lumina SS (aka Pontiac GTO) – Zaid Jul 17 '14 at 22:02
@Paulster2 : I'll have to check the RPM drop, but the issue persists regardless of fan speed. Engaging the A/C switch is enough to cause the voltage to drop. – Zaid Jul 17 '14 at 22:04
up vote 4 down vote accepted

As highlighted in the question comments, the culprit was the vibration damper on the crank pulley that had failed, causing the pulley center and outer ring to have some limited slip relative to one another.

I'm happy to say that the following symptoms were resolved.

  • With the A/C disengaged, the crank pulley was spinning at a limited speed. This was also causing issues slight engine overheating and reduced power-steering assistance that I did not believe were related at the time of posting the question. With the new crank pulley in, things are much better; no overheating, A/C runs as before and the steering is easier.

  • Engaging the A/C provided additional load on the crank pulley that was enough to cause it the outer ring to stop rotating. This was what caused the 'Check Alternator' message to appear and battery voltage to drop.

  • Belt squeal is vastly reduced, so I probably will still have to replace them.

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