Headlights dim and brighten?
 

I noticed on our 7 hour trip back from Erie, PA to Lancaster, PA between 6pm and 2am that the headlights dim and brighten once in awhile randomly. I thought it was the A/C compressor turning on and off like my Honda did. But I turned the A/C off and it still did it.

Have you guys noticed this too?

What settings did you have on the climate controls during that trip (the air flow direction)? If you had them in Front window defrost, Front window defrost + floor or just floor, the A/C will go on even if the A/C buttons is not on.

Yeah, it doesn't make sense and it's not mentioned in the manual, but that's the way it is. :D

if true, then that SUCKS! and now Mazda is on my shit list... I hated that the Chevy I had did that as well. I noticed that you can not control where the air flow is from in defrost either... once again, the car manufacturer thinking for the driver.... guess it is time for the same solution I used last time, by-pass the control signal to the A/C compressor clutch with a switch of my own.

I like to drive with the heat on the glass and do not need the A/C on all the time.

hehe JJB, if you don't believe me, you can experiment on your own. Just wind down your windows and listen for the A/C compressor to kick in while you mess around with the climate controls (with the A/C button off) :)

This is my first car that has such 'programmed' A/C fucntion. Yeah, I'd rather have full control myself.

I read in another forum that there are micro-switches in the vent-direction knob that triggers the A/C and you can remove them so it won't turn on the A/C by itself. I'll try to find that post and put it here...

I had the same problem with my 2001 LX2.0 ,turned out it was the altenator ,it was replaced on warrenty . No more problems . Have the dealer hook the car up to the dianostic computer ,that's how my dealer found my alt. was bad . Malcolm Cole

We had our settings on middle heat (cold/hot) and the air flow was on feet, and fresh air coming in.

I thought it might be the alternator too cause my civic with aftermarket pulleys will do that, but her car is brand new.

Then I suspect it's the A/C turning on and off. Your P5 is pretty new, so there might not be that much corrosion on your battery terminals.

I would first try to drive it at night again with the air flow blowing to face or face + feet and see if it happens again.

If it does, then it could also be a bad alternator as Macklum suggested.

Re: Headlights dim and brighten?
 

hmm Subs and Amps can do this...you may have a bad alternator..or there is the A/C still running. I really need to look into that.

No the A/C is not on. My wife took it to the dealer for the 1000 mile check up and they said it's the fan turning on. They said the alternator is fine. Is that normal? For the fan to turn on when driving on the highway?

The fan turns on when to help cool down the coolant.

This happens to my car (and other p5's i've seen) even when idling.

I would think it'd be more prevalent on a highway since you are probably creating much more heat while driving.

Even driving at night when it's 20 degrees out? I would think the air hitting the radiator would be enough to keep the car cool, so the fan doesn't have to turn on. I know my Civic doesn't do that.:dunno:

To me it's not normal.

a/c cycles on defrost to keep the compressure and o rings oiled, it is adesign by most manufactures

Well if you noticed we're not using A/C.