Voltage drop from A/C

[SourDeez 10+ year member]

So I get voltage drop when I have my ac on (no subs or amps currently installed)

Think my alternator is bad?

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[subzero 5,000+ posts]

Yes. If it is not kicking on then yes. your need to have it checked.

 

[SourDeez 10+ year member]

What do you mean by kicking on?

 

[sobe3yourself. 10+ year member]

is it just for a split second? how big is the drop? a small drop should be normal seeing as how it is an additional strain on your electrical system.

 

[SourDeez 10+ year member]

It's a big drop for sure

 

[subzero 5,000+ posts]

What do you mean by kicking on?

you alt is not always on. only starts at set RPM. and the AC is not always engaged.

So, if you engage the AC and notice a voltage drop, it could be that your alt is not charging very good. or that your batteries are not hold a good charge to sustain the new load created by the AC.

 

[AnEffinCookie]

When the A/C compressor's electromagnetic clutch is engaged it definitely draws some juice to keep that sucker locked in. Plus the a/c relay engages the fan for the engine and the cabin blower motor, that draws some current too. The amount of normal voltage drop is something I do not know, but it should not drop too much. Check around online or check a friends car and see how much the voltage drops when the clutch is engaged. Could be nothing, unless it is a lot, then there might be a problem with the battery or alternator.

 

[keep_hope_alive Premium Member]

agreed with above.

all depends on the vehicle, engine size, alternator size, and any other electrical loads.

as mentioned, alternator output varies with RPM. at idle, you're not getting much output from a stock alt.

how low is the drop? at rest, your battery should maintain 12.5-12.8VDC. the alternator should be able to maintain 13.8-14V.

if you have a standard lead acid battery, make sure your water levels are adequate.

 

[jaws031]

My battery died sometimes when i cut the car off it wouldnt crank when i tried to start it. I had my battery and alt checked they say they were both good but prob still continued especially during the night from my hid's. I changed batteries and after the car sat over night new battery was dead. I took the car to get the alternator rebuilt. The man at the shop told me my belt wasnt tight enough to make the alt do what it needed to, so i tightened it and lately the car havent died on me. I have a 82 malibu and the only electrical components are HIDs viper 5901 thats all no radio. I dont know if this will help you but it could just be a bad alt belt or its not adj properly

 

[keep_hope_alive Premium Member]

i used to have an 82 malibu. yes, a loose alt belt will prevent proper charging.