Could it be the compressor?

[asphaltjunkie]

94 S10 Blazer 4.3 auto 2wd. Battery guage likes to dip way down while driving with the a/c on, more so when stopped at a light. In park it is normal. Dips down farther at night with the lights on. New alternator, new battery, still having the same problem.

Could my compressor be putting that much strain on the charging system? When stopped at a light, if i turn the a/c off, the guage goes back to somewhat normal.

Is this even remotely normal for these trucks, or is this a sign my compressor is about to lock up on me?

[cool cat]

How low are the RPM's dropping?

I have a 94 S10 V6 (CHOOOOO$$$$$$ CHHHHOOOOOOOOO$$$$$$$$$$$$$$$$$$), and I'm not having that problem with my AC on.

[homealone]

It's more likely your blower motor than the AC clutch unless it's actually dragging so much you're near stalling.

Adjust your blower speed while watching the voltage and see if that makes a difference.

On top of that, it may be your alternator. If the diode if faulty, it won't kick up the amperage when a load is put on it.

[asphaltjunkie]

Turning the blower down does help a little, but turning off the a/c all together pretty much fixes the problem. Even with the blower on low, if the a/c is on, especially at night with the lights on, at a stop you can see the headlights dim down and then brighten back up once I give it gas. Put it in park, and it's like there's nothing wrong though. The alternator is brand new, and so is the battery. I've never heard of a compressor dragging a motor down that much, but it's looking like that's the problem.

Another theory I have, however, is the strength of the battery itself. All the parts stores call for a "75" series battery, which carries a max CCA rating of 690. There's room in my battery tray for a full-sized "78" series battery that has a max CCA rating of 850. I'm wondering if a stronger battery would help solve the problem.

What about upgrading to a higher amp alternator? I hear the 140 amp alternator for a Suburban is a direct bolt on. Would that possibly help any?

[homealone]

The CCA of the battery really applies to start power. When the truck is running, power is supplied by the alternator.

The current alt should be adequate for the truck unless you have added extra load to the system. Stereo, etc.

As for being new, new parts can be bad also. I would have them checked.

Battery guage likes to dip way down while driving with the a/c on, more so when stopped at a light. In park it is normal. Dips down farther at night with the lights on.

This here says you have a charging problem. You can do a basic check if you have a volt meter. With the truck turned off, your battery, if charged, should read about 12.5V. Running it should be about 13.5V if the system doesn't see a large demand. Next, turn on the AC, fan on high and lights. This should energize the alternator and kick it into "high" output. At this point you should see 14+V.

If you don't either of these, you have a battery/charging problem. At this point, like I said, have the battery and alternator checked. Check your battery connections, check the wiring to the alternator, make sure it's connectors are seated properly.

Now, if all that checks out, I'd lean more towards the blower motor being the issue over the AC clutch. The clutch is an electromagnet and unless it's completely shorted, I don't see it drawing that much amperage.

Try running it again, Leave the AC off but run the blower motor and see if you get the same results.

[asphaltjunkie]

Got to work today and tested the alternator. In park with everything off it put out over 14v, and 48A at idle. With it in drive, with everything on high, however, the damn thing dropped to 12.6v, and less than 30A at idle. But the question now is, is the alternator bad and causing my problem? Or is something else putting that much of a strain on the system? You mentioned adjusting the speed of the blower, so i tried that, and it helped a little, but not quite as much as turning the a/c off completely, or putting it back in park.

[TexasT]

Take the alt off and have it load tested at a parts house. I would think it bad if it drops to 12.6v .

[Blackpony]

Check your grounds and make sure the cables are in good shape.

[asphaltjunkie]

Take the alt off and have it load tested at a parts house. I would think it bad if it drops to 12.6v .

I load tested it at work on the truck.

I'm just stumped as to what is putting that much of a strain on the system. Someone here mentioned the blower, I had a mechanic while at work tell me the compressor/clutch may be dragging/on its way out the door.

On the way home tonight I stopped and fiddled with the a/c and blower. The guage stayed relatively the same switching from max a/c to normal a/c to vent and off. However, with the blower on high with any of those components on and switching it to low gave the largest improvement on the guage.

So now the question is: blower motor? Or blower motor resistor/relay?

[TexasT]

Are the contacts and such clean in those two items? The blower on the burb I drive goes out every few years with a squeal, might just replace it and the resistor. Not exorbatantly expensive.

[jyro]

put a smaller pulley on your alternator