Charging with A/C on?

anealysr · June 16, 2002

Does anyone else see this on their truck. When the A/C is on and being stopped in gear the charging gage drops quite a bit. As I get back up to hwy speed it climbs back to 14 volts but not quite as high as when the A/C is off. Is my altenator going out? Or is my fan motor drawing too much current. I remember back in the old days GM had a wear problem with fan motors. Have replaced my share on cars when the high speed would quit. I know the alt. had to work it's butt off on my truck with everything being electric. But I only have 57000 mile on the truck. Well Thanks guys. Love this forum.

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95 Silverado · June 17, 2002

My voltmeter drops back also. 1 to 1 1/2 volts seems to be typical. the clutch coil, and fan motor pull it down, at night the additional load of the lights is added on. if it was always that way I wouldn't worry about it. If you notice it being more than usual have it checked out, could be a weak battery or alternator.

June 17, 2002

Mine does the same thing.

I attribute it to

1) RPM decrease with the A/C engaged

2) A/C fan is running

3) Engine cooling fan clutch is engaged

Mine's done it since day one. I wouldn't worry about it at all.

MarkD · June 17, 2002

As long as you are above 12.8 Volts, I wouldn't worry about it. The solenoid in the AC compressor clutch pulls quite a bit of power. This, coupled with the extra load on the engine, and various other electrical loads attributed to the AC, use quite a bit of "juice". I am not sure what our alternators put out at idle (500-600 rpm), but I would not consider an alternator weak for not being able to hold peak voltage at this rpm.(especially if it is remedied by 1000-1200 rpm)