Okay so my 2003 3500 with 130K miles has an A/C issue. Over time it has quit blowing cold, checked codes last night and found the P0646 Low Voltage at the A/C clutch relay. Swaped out the relay with an extra and no change. I am still running the original batteries, could the batteries be the problem? Thank you in advance for any insight you all may have.

 

If it has quit blowing cold then you more than likely have a leak in the system. Hook up some a/c guages and see where you're pressures are at.

 

Hooked up gauges, and everything was good. reason I am wondering if batteries could be the problem is that when it was working it took longer each time before it would kick in. Could the batteries be so far gone that the computer is not giving up power to the A/C until the batteries are fully charged? I know it's a shot in the dark, but with ten year old batteries ya gotta wonder.

 

Seems like I read somewhere that the compressor clutch wire gets rubbed somewhere and an open wire creates a short causing other issues. I wonder if you don't have a slight bit of this going on and its giving you the error to the clutch...........just a thought.

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10 years is quite a time for batteries.....I got 8 out of mine and all kinds of wierd things started happening. New batts cured my problems. Is your compressor running at all? If the clutch is engaging and it still blows warm then you have a leak in the system that needs attention. If it's not engaging then, yes the electrical system might be playing a part in that or if your clutch is wore to the point that your air gap is out of tolerance that will cause issues as well.

You say your pressures are good but just remember that any air in the system will cause a problem......you want liquid only....hence, pulling a vacuum before charging. Keep us posted.

 

Just replaced the Batteries. A/C is blowing cold, but truck is hard to start and seems to have a lag when accelerating. Anyone know if the computer resets when all power is disconnected?