Too much power to ac control module

[HawgHunter]

Good afternoon folks....I've got a gremlin I need a bit of help catching. I'm driving a 98 k1500 with the 5.7 and she's burning up control modules. I tried the fix with the control module, which lasted right up till I gave it a bit of throttle....just burned the board further up. After doing some looking, the previous owners have definitely done some work on the wiring under the dash.....oh boy! So, I took it to firestone and they told me the control module is getting 18 volts. Yikes! And that I would need to take it to a specialty shop to have all wiring traced. So here I am with 2 questions in tow.

First, any ideas what would cause me to have that much voltage at the control module?

Second, can I just run new wiring for battery, ignition and grounds to known good power sources and maybe bypass whatever mumbo-jumbo wiring they have going on?

It's getting hot here in Houston, Texas and I would love to have some cool air on those hot days.

Edit: I've posted a pic of the burned out module below.

 

[AK49BWL]

18 volts?? What's your volt meter in the cluster say while you're driving? Sounds like you have a faulty voltage regulator in the alternator to me, and if so, it's surprising the HVAC controller is the only thing you've blown out...

 

[HawgHunter]

The cluster meter is reading normal as is my volt meter when I tested the alternator and battery....around 14 volts. No other issues are occurring other than blowing the ac module.

 

[AK49BWL]

Definitely time to go through your wiring then.. I cannot think of any way the module would be seeing 18v, that just seems a little out there to me.

 

[Erik the Awful]

If the Firestone in your area is anything like the one here, you'll want to double-check their work. While I was deployed my wife took our '99 Suburban in for tires and they told her the ball joints were bad and it would be a solid grand to replace them. I told her to tell them to f* off and park the truck at home. When I got back I jacked the truck up and the ball joints were tight. The idler and pitman arms were bad.

 

[df2x4]

If the Firestone in your area is anything like the one here, you'll want to double-check their work. While I was deployed my wife took our '99 Suburban in for tires and they told her the ball joints were bad and it would be a solid grand to replace them. I told her to tell them to f* off and park the truck at home. When I got back I jacked the truck up and the ball joints were tight. The idler and pitman arms were bad.

One here told my dad that they couldn't align his truck because the idler and pitman arm were bad. Quoted him around a grand to replace them as well. They're both fine.

 

[skylark]

This is exactly why I walk customers out to the shop and show them what is wrong with their vehicle.

If the Firestone in your area is anything like the one here, you'll want to double-check their work. While I was deployed my wife took our '99 Suburban in for tires and they told her the ball joints were bad and it would be a solid grand to replace them. I told her to tell them to f* off and park the truck at home. When I got back I jacked the truck up and the ball joints were tight. The idler and pitman arms were bad.

One here told my dad that they couldn't align his truck because the idler and pitman arm were bad. Quoted him around a grand to replace them as well. They're both fine.

 

[RawbDidIt]

This is exactly why I walk customers out to the shop and show them what is wrong with their vehicle.

I'll pile on here. Firestone ain't the place to have that work done. Obviously there's tons of people with great experiences, or the place wouldn't be in business, but a buddy of mine got his oil changed there, they didn't put the fill cap back in and he took off from there, drove it 2 hours till the oil pressure light came on and alerted him to the problem. Unrelated incident, but the same thing happened to my girlfriend, different Firestone, but the guys both must've skipped the same day in training.

The TL;DR here: either check their work yourself, or take your vehicle to a qualified mechanic, not a tune-up shop.

How in the world you'd get 18v there is beyond me, everything is either 5V from the ECM or 12V (ok, 13.5-14.8ish) from the batt/alt. That said, also take a multimeter and check the voltage at the alternator output measured against the case of the alternator. The gage in the dash is just a glorified working/not working dummy light, it's not accurate... at all. My truck with all the wiring upgrades and the 225A output reads between 13 and 14 volts depending on the phase of the moon, day of the week, and the general temperament of my truck that day, but with a multimeter it runs 14.6V all day, every day. Anything higher than 14.8V (IIRC) indicates the voltage regulator is out, but at 18V I'm imagining you'd have far more issues than your HVAC control as mentioned above.

Sent from my SM-N976V using Tapatalk

 

[HawgHunter]

After running through all the connectors for the module and the alternator I couldn't find anything above 14 volts. I'm starting to think they just blew me off not wanting to mess with it, as all I wanted was a diagnosis to fix it myself. I'm going to tinker with it a bit more today in the hopes of finding the cause....if not, I'll definitely have to take it in to a real shop. I'll keep yall posted.

 

[HawgHunter]

Here's a pic of where the module burned out this time after the fix (aka: glob to the left. The burned out path is linked to the ac switch on the module. Hopefully this will shine some light on my problem.

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