Hi I have an 07 Chevy Tahoe LT and my a/c just started to drain my battery voltage. This only happens when I turn the a/c on and the voltage begins to go down. When I turn it off, the voltage goes back up. The engine light does not come on. The battery and alternator are new, had them for about a year. What could be causing this issue?
When you turn the AC on there's a large voltage draw.
The cooling fans will kick to high, the blower motor will run, and if the AC compressor has a clutch that has to be energized.
You need to figure out why the battery charge isn't keeping up.
You have a pretty new alternator and battery.
You can perform some of this diagnosis with something like a cheap Cen-Tech multimeter which you can buy at Harbor Freight or online from Amazon or ebay for around $10.
You'll begin your diagnostic by turning on the AC, switching the blower motor to high, (and turning your headlights on) to force the computer to command maximum charging from your alternator.
You'll be determining if this is a battery problem. an alternator problem, an issue with a bad battery cable connection or corrosion in one of the battery cables causing voltage drop from the alternator to the battery, or if the computer isn't commanding the alternator to provide maximum charge to the battery under heavy electrical load.
I found a video of a guy doing some of this using a cheap Cen-Tech multimeter.
He's using the multimeter to measure the alternator charge at the battery.
After that he's moving the multimeter probes to test for a wiring issue or voltage drop.
First, he's eliminating the possibility of a bad connection or voltage drop inside the battery negative cable by measuring the voltage drop between the battery negative terminal and the alternator body.
Then he measures for voltage drop between the B+ terminal on the alternator and the battery positive terminal.
The only part of his video I don't agree with is his statement that under full load you shouldn't see the charging rate at the battery drop below 12.7 volts. I'm of the opinion that it shouldn't drop much below 14 volts, and even then, just intermittently. You want to see the charging rate during full electrical load between 14 and 14.5 volts.
Other than that it's a great tutorial and a good starting point for you. It doesn't cover the computer control of the alternator but you have to do these tests first before moving on to that.
I didn't mean to overcomplicate this and if you watch the video you can see that all the guy is doing is moving the multimeter probes around.
Here's the video
https://www.youtube.com/watch?v=LGB6ZEjGm7Q
Thank you, I do appreciate helpful video.
Interesting that it isn't blowing any fuses.
Is the engine RPM dropping as well?
This problem just started this week. I ran a/c last week with no issues. I will definitely check the fuses. I do not lose rpm but my rear window does open when the voltage drops as well.