Weird Electrical Issue

SSnakeAce · August 10, 2009

Hey guys,

First off, I'll start with the truck. It's a 94 Silverado extended cab, 106,000 miles, 5.7L. Never had a single problem out of the truck, and today is the first time the Check Gauges light has ever come on in the truck because of a problem.

Was a scorcher today at 95 degrees, and I was helping my friend move some stuff into her apartment. Had the AC on full blast, but not in recycling mode, for the hour long trip to the apartment, then left the truck sitting for about 3 hours while we got everything moved. Went to make the trip home, still with the AC on, and about halfway there we started noticing that the blower motor for the AC would start speeding up for a couple of minutes, then slow back down to normal max speed. A few minutes later, the truck just stalled out entirely, showing me the battery light and the check gauges light.

Pulled off the road, cut it off, and cranked it back up. Cranked up perfectly fine, and a few seconds later cut back off again. Tried one more time, and cut the AC off this time. Truck kept running, and the battery gauge showed just over 12v. Put it in gear, drove my friend home and then back to my house with no further problems. By the time I got there, the gauge was now showing 14v. Got my dad's voltmeter out and checked the battery, was showing 14.03v when running with no ac, 13.93 with ac on full blast.

We noticed while we were fooling around with it that the REC light came up on the control unit for the AC. I never turned it on, Dad says he did. Tried turning it off, and it wouldn't. Had to turn off the AC entirely to get it to cut off, and the recycling mode started working fine after that.

Any ideas? I'm currently thinking that the AC is drawing more current than the alternator is putting out, giving a slow drain on the battery. We also discussed the AC possibly getting in a bind, which may be possible because it does seem like it's not cooling as good as it used to. My last option is something wrong with the control unit.

Oh, and I have no idea how long it may have been acting up like this. The last time I ran the air before this for any real length of time was probably 4-5 years ago. I'm one of the people who can have the best AC in the world, and still prefer having the window down.

bill190 · August 10, 2009

With the engine running, the voltage should always be 13/14 volts.

This is your alternator charging the battery.

I'm thinking your alternator is going out. Sometimes heat and/or operation at a faster speed will make an alternator not work, but they will work when cooler or operating at a slower speed.

As to the A/C, this is probably electronically controlled. Electronics go "haywire" on low voltage. If you are running just off the battery, the voltage could get to be low and make the A/C do weird things. Your A/C is probably fine.

kuhl_530 · July 19, 2010

I know I'm ressurecting an old post, but my 95 A/C does the same thing. If I have it on normal A/C and not recirculating, while I'm at an idle it will start recirculating on it's own. I think it's an electrical feature to keep the cabin filled with cool air. When at an idle, the compresser is turning slower, and little air is moving over the condenser causeing the refrigerant to run at a higher pressure, and thus a warmer temperature. By recycling the interior air, the system is cooling air that is already cool, making it more efficient and preventing your hvac from pulling hot outside air across your warming evaporator.