85 k5 silverado
 

New to forum, looking for some help! I put a Fitech system on my truck, finding that with the AC on the battery voltage drops and unit shuts down. Put the carburetor back on, and same thing, only now Electronic ignition starts to shut down. I was thinking fan motor resistor?? All new AC system.

Welcome to the Blazer Forum.

A/C can be the culprit in several places. Compressor clutch, Fan, Fan wiring, Relais. Need to measure the voltage drop or amperage.

Moving according the rules in the "New Member" section to electrical & lighting.

I agree with Marc, you really need to check your system voltage and narrow down the draw. It is possible that you have too much electrical demand for the stock alternator to handle or just something drawing way too much due to a faulty component. I'm not sure if there are many places left that will test your alternator for you, but most all of them will require the alternator off the vehicle. A simple voltmeter (multimeter set to DC Volts) on the battery to see normal & AC-on voltages will tell you if you have a problem in that area. Let us know what those numbers are and we can work from there.