Mustang89LX

I own a 89LX 5.0 automatic with an 200 amp alternator and a flex-a-lite black magic extreme fan. My problem is that when the electric fan kicks on and I have the A/C on cold or hot the volt gauge will drop to around 10 volts and also the car will almost die, I have replaced the IAC motor. I also tried a shorter belt that doesn't go around the compressor thinking that the compressor might be bad or locked up and the volts still drop WAY down. I had an 130 amp alternator with a 49mm overdrive pulley but and the volts don't drop as bad as the 200 amp does. I do not have underdrive pulleys on the car and I also upgraded the power wires to 4 gauge to handle the extra power of the 130 and 200 amp alternator. Any help would be nice

SpectreH

Is it possible that the 200 amp alternator creates so much load that the belt slips, reducing the alternator's ability to charge?

Mustang89LX

How would I check for belt slip? The belt dosent make any noises when running I have also tried 2 belts and the belt have good trension on it I also had the alternator tested and its charging underload

SpectreH

I'm not sure how to check, but it just seems like the higher output alternator is not putting out at lower RPMs like it should. Slipping on the belt would be one possible explanation. Hopefully someone else will have further advice.

americanfisher93

Is the 200 amp name brand? And what was the reason for replacement? Cheaper alternators may push out less amperage at idle them from your 140, but once you rev up the engine it'll shoot up to 200 versus only 140. Grab a volt meter and see how many volts it pushed out at idle, could be a bad alt, it's happened before. Did you run that fan with your 140? Either way a electric fan shouldn't take much at all to run, so best guess is a bad alt.