Battery light goes on in my FORD FOCUS WAGON 2002 only when i am starting up AC or when ideling slow in traffic guy at NAPA says it maybe a switch to a sensor for AC my brother is a mechanic and may save me from a garage or dealership have you had anyone else report this problem
Have you had the battery and alternator tested? That’s where to start. If the battery is the original, it’s probably time for a new one.
battery is only a year old my husband tested voltage(hes an electrician0 voltage at 14 where it is suppose to be but my brother noticed both fans klck on upon immediately when car is started then voltage goes down to 12 and light comes on
could the problem be as simple as a switch gone bad
Alternator may be failing. It sounds like it can’t keep up with the load. Maybe one of the diodes has popped?
The next step would be to clean all the battery connections (both ends of both cables) and any ground connections between the body and the engine.
The fans shouldn’t start immediately unless the air conditioning is on.
the reson we feel it is not the alternator is because it still carries a 14 amp load which is good until u turn the AC on has anyone heard of a bad sensor witch regulates the fans and therefore the car is not bogged down by the load and what is a diode
anyone else have any suggestions
Have you checked the battery voltage without the engine running. A battery reading of 12.6 V would be fully charged, 12.1 V is about 25% charge. A reading of 11 Volts or less means the battery has a bad cell and needs to be replaced. When the battery on my 2000 Blazer was discharged to 12.1 V, it started having driveability problems (high idle, torque converter lockup not engaging). Once the battery was fully charged the Blazer ran fine.
I’ve had batteries go bad in ten months with no warning.
Ed B.
You need to check and see how many amps the alternator can put out. Dont expect it to reach its rated output but within 10-15%.This sounds exactly like the alternator cannot handle the load. Google diode
TO NYBo
I just cleaned post and checked connections what i noticed is when car is sitting and running with AC on it almost comes close to stalling when fan kicks on
14 Volts is not 14 Amps! It sounds like the alternator can supply a few amps, but can’t supply all the amps required when the AC is on. The voltage should stay at 14V or so all the time, even with the AC on.
If it’s going below 700 RPM, then look at the IAC.
WHAT IS IAC yes I am a female not to familiar with these things but I am trying to diagnose problem w/o the help of some fancy garage
Do you mean it has 14V under load or that it is really 14 amps (14 amps would be about 160 watts.
Many auto part stores will check the battery and the charging system for free. That is where to start. I tend to think you have a real problem and it is going to get worse, not better.
Being female does not mean you don’t know anything about cars. Don’t use that as an excuse. 
If you are not interested in learning, that’s fine, male or female.
OK IAC is Idle Air Control. It controls the idle speed. This one you likely will need to take to a mechanic to check out.
Idle Air Control valve. It’s how the computer controls the idle speed of your engine. Cars with Electronic Throttle Control don’t have (or need) them, but I think that yours is not ETC. The IAC may be bad, or it may just need a really good cleaning.
Googled diode THANK YOU THANK YOU could it be a bad diode inside the alternator w/o the whole alternator being bad
My brother the mechanic just e-mailed me and said ask anyone out there if theyve seen the red wire to the alternator cause a short
It’s possible for the alternator’s voltage output to be ok; but, it’s amps output can be too low. Many larger auto parts stores will do volts and amps checks on your battery and alternator in the car, curbside…for free. Just ask.
Since both radiator fans are running when the engine is cool, it could be the ‘engine coolant temperature sensor’ is bad and telling the engine computer that the engine is always hot. Using this information, the engine computer turns the radiator fan(s) ON. Or, or, the pressure switch (or its wiring) is sending a signal to the engine computer, and the engine computer is turning the radiator fans on. Testing the wiring, pressure switch, and the engine coolant temperature sensor will reveal which is the culprit.
Get the wiring diagram from the repair manual, or an online source, and turn hubby loose with a multimeter.