This isn't happening with my 4Runner, but with my 84 Tercel. When i start the car with the A/C on, my Brake light and Battery light stay on (even with the parking brake off). They only turn off if I turn the A/C off, or after i drive a little way and the compressor disengages. When i Drive it with these lights on , when the RPM's speed up, the Fan speeds up, and as RPM's decrease, the fan speed decreases.

Not that it's a problem that i have to fix, but it is an interesting problem that i'd like to know what's happening and why.

Any ideas?

It almost sounds like the voltage regulator is going out, but i don't see what that has to do with my A/C

Steve

 

Is is possible that the idle up is not working with the A/C engaged, and your RPM is too low for the alternator to start working? If you rev it up in place do the lights go out? I had a similar problem in my 91 camry.

 

I can rev it all i want but the lights won't turn off. only when the compressor disengages.

 

>>Not that it's a problem that i have to fix<<

I'm thinking you might be wrong there. Sounds to me like your alternator is dying. On my '85 Runner the same lights show up when the alternator isn't putting out enough current.
It's a pretty stupid way of setting up code lights, but it is what they went with in that time period. I'd say get the alternator tested and get ready to either put in new brushes or buy another one.

 

i thought it may be that, but then why would my blower fan speed up as the RPM's increase (then as soon as the AC compressor disengages, the drops to normal), it's almost as if there is too much voltage or something like that.

 

As a complete WAG, I would say that as you rev the engine the greater RPMs up the output from the dying alternator. So, maybe the fan isn't actually speeding up when you bring up the RPMs so much as it finally get the juice necessary to run at the right speed.
I guess it could also be overcharging. Seems like the battery would let you know in that case. Wouldn't it be getting really warm if it was getting too much charge?
Just guessing