Big voltage drop when the AC compressor cycles on.

[L3V3L1]

Like the tile says, the voltage drops from 14.3 down to 11 when the compressor cycles on. I'm checking the voltage at the jump terminal. If I press both window down buttons, when the windows are already down, I get the same drop. Where should I begin to troubleshoot this?
TY

[Timeless]

What is the condition of the grounds? Dirty grounds can cause a decent amount of voltage drop.

[JBaker4981]

Does it stay down at ~11V or is it dropping and then bouncing back to normal?

[L3V3L1]

Does it stay down at ~11V or is it dropping and then bouncing back to normal?

It bounces while the compressor is engaged, from 11.4 to 12.5. When it cycles, off, back to 14 +.

[L3V3L1]

What is the condition of the grounds? Dirty grounds can cause a decent amount of voltage drop.

I'll have to research ground locations and check them. Ty

[David T]

If you are checking this while the engine is idling, the alternator cannot output it's full rated current. Try your checks with the engine running about 1,000 RPM's.

[DavidProehl]

Have you verified all your fuses are fresh? I had a similar issue years ago when I was using fuses that were 10-15 years old. Swapped out the fuses and all my strange voltage drops disappeared.

[TheFover]

Mine also drops this low with the compressor is on. Even lower with the headlights. Brand new alternator with super tight belt too. I'll have to try the double window thing tonight.

[painterdave72]

Check the main wire from the post to the alternator also.. mine was a replacement from about 20 yrs ago and eventually it corroded enough to cause a massive voltage drop like you are describing.. replaced it and voltages stay up at 14 with ac and my sub and lights etc etc..i do have a larger amp alternator though but you get the idea..