Air Conditioning Problems

[Pudnut]

Ok this is a really weird problem. But I have a 1990 Ford Bronco that is having this problem with the AC. The problem is this. I turn on the AC while the vehicle is running and the voltmeter drops down to about half. Supposedly this is still in the normal but the truck has trouble starting thereafter. Due to battery drain no doubt. So I was wondering to myself, is this normal? I dont think it is and I feel like it could be a short somewhere in the system? But maybe there's more to it than that.

[Dan_in_WA]

The A/C clutch will certainly put an extra burden on the electrical system, but unless you're blowing fuses or have replaced some fusible links with larger wires, I'd look for something else besides a short circuit.

Does the engine idle speed drop when you turn the A/C on? Is your alternator putting out enough current?

Does the voltmeter come back up if you rev the engine?

I recommend checking out the alternator/voltage regulator first.

Good luck!

[Pudnut]

The fusible link from the alternator to the solenoid was recently replaced by a mechanic from the local shop so if that is the problem I'll have to be more careful about where I take my truck in the future. But the RPM remains constant and as far as I know the fuses are all working properly but I'll look into it. Thanks for your input.

Also I found out that its not just when the AC is turned on, the heat also causes the meter to drop. And another item to add if this makes any difference is that I also replaced the positive battery cable with a 4 gauge cable recently.

[Dan_in_WA]

Originally Posted by Pudnut

Also I found out that its not just when the AC is turned on, the heat also causes the meter to drop.

The A/C compressor will run if you put the controls on Defrost, too. You don't want moist air being blown onto the windshield in the wintertime, and this is how Ford's engineers de-humidify the climate control air.

Does the voltmeter drop if you're just running on the Vent position?

What does the voltmeter do if you change fan speeds?

I'm still thinking that your problem is in the alternator/voltage regulator, especially since the fusible link for it was just replaced. That fusible link died for a reason - probably the same reason you're seeing the voltmeter sag when turning on the accessories. Bad diode in the alternator, perhaps? Or the voltage regulator is toast.

[Pudnut]

Ok I've had more time to look at the problem. Here is all thats going on. I get the feeling you may be right on the money with this problem. Anytime the vent fans are running or their speed changes the meter drops. Also whenever I operate the front door and rear tailgate power windows it does this as well. My headlights do not work, I just found that out tonight . So if the voltage regulator is dead, and you're probably right. I should buy a new alternator; Correct? I believe my model uses an internal voltage regulator inside the alternator so I would either have to fix the alternator with a kit or buy a new one.

Thanks so much for the help.

[Dan_in_WA]

Yes, I'd go with a new alternator. Get the best quality replacement you can find - the cheap ones will fail within about 18 months (my experience). A few extra bucks spent now will pay off later.

The store you go to for your new alternator can probably test the old one, just so you know for sure.

[Pudnut]

I had the alternator tested before the fusible link was replaced. The guy at AutoZone said it was working but I don't know if they just test to make sure its putting out enough electricity or if it tests the voltage regulator as well. But considering that it wasn't doing all of this before the link was replaced I'd have to say that they didn't test the regulator.

Again, thanks for the help. It was very useful advice.