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Jerry Newton
Jerry Newton, Chevy Technician
Category: Chevy
Satisfied Customers: 4438
Experience:  ASE Master Technician, L1, Master GM Technician. Over 20 years of bumper to bumper GM experience.
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Power continues to the HVAC controls on my 98 tahoe when the

Customer Question

power continues to the HVAC controls on my 98 tahoe when the ignition is off. i replaced the ignition switch and no change there is a significant draw down of the battery
Submitted: 1 year ago.
Category: Chevy
Expert:  Gary replied 1 year ago.

the blower motor will run with the key OFF ?

what exactly is staying on with the key OFF ?

Customer: replied 1 year ago.
The blower motor will operate in all speeds with the key off also the rear blower motor. once the electronic 4wd switch kept switching back and forth between 2 an 4wd when i shut the vehicle off, but that hasn't happen again yet.
Customer: replied 1 year ago.
the ac and the recirculation and the rear defrost button all will light up when pressed. The radio stays off, turn signals, electric windows all stay off
Customer: replied 1 year ago.
i pulled the fuse out thats marked for 4wd and i can hear a clicking under the dash like a relay is operating. this occurs without the ignition on. i can pull the the big fuse out for the blower under the hood and it only stops the highest speed from working. the other fuses inside the cab marked for the hvac will not stop the blower when removed.
Expert:  Gary replied 1 year ago.

if you remove the heater ac fuse from the inside fuse box it will stop draining the battery ?

Customer: replied 1 year ago.
no. it wont even stop the blower.
Expert:  Gary replied 1 year ago.

so fuse 12 out of the inside fuse box and the 40 amp fuse called blower out of the under hood fuse box with the key OFF the blower will still work ?

Customer: replied 1 year ago.
not now for some reason but when i take the fuse 5 out for the rear a/c and turn the control switch there is a clicking in the rear like a rely is operating. When the 50 amp is in and the a/c blower is out and the number 5 is in the blower runs. when 5 is out the blower stops. when 5 is in and 12 is out the blower runs
Customer: replied 1 year ago.
i think its in the rear a/c unit
Customer: replied 1 year ago.
for some reason now if number 5 fuse is removed then the main HVAC switches work properly (only with the ignition). However the rear a/c continues to get power and will operate without the ignition on. all rear relays work properly and the rear resistor also. I the number 5 is replaced the main HVAC will operate with out the ignition
Expert:  Jerry Newton replied 1 year ago.

I'll take a swing at this.

Does fuse 5 have power with the key OFF?

Customer: replied 1 year ago.
Expert:  Jerry Newton replied 1 year ago.

OK, it shouldn't have power, and from what I'm reading here, it would seem that power is backfeeding through this circuit and keeping the front HVAC panel lit up. So, just to clarify, if you remove this fuse, everything shuts off like it should?

Customer: replied 1 year ago.
When #5 is out everything works correctly except the rear blower. It works without the ignition on
Expert:  Jerry Newton replied 1 year ago.

OK, that's as it should be.

The root cause here is that there is power applied at fuse 5 when there shouldn't be. Let's investigate that. Remember that if power is inadvertently applied to a circuit that shouldn't be energized, that power will branch out to any other circuit that's connected to it, so I'm not surprised that you have a serious battery drain, HVAC panel lit up, etc. This all stems from fuse 5 having power when it shouldn't have.

Let me look at some schematics and see how I'd attack this.

Expert:  Jerry Newton replied 1 year ago.

You can see in this drawing how fuse 5 is connected to the other fuses on that branch by an orange wire. Presumably, this whole circuit is energized, which explains the battery drain. This comes from the ignition switch. The first thing that occurs to me is: do you have an aftermarket alarm or remote start installed on this? Any kind of aftermarket device that is tapped into the ignition wiring?

Customer: replied 1 year ago.
Nothing except an electric trailer brake. Not sure what it is connected to
Expert:  Jerry Newton replied 1 year ago.

That's a potential issue, since the brake fuse is one of the fuses energized inadvertently. Remember that this power source can be from any branch of the circuit, you're only noticing the rear blower and HVAC panel issues because they're obvious, but lots of other things are lit up here that shouldn't be.

Unplug the brake controller, and let's just see if that makes any difference.

Customer: replied 1 year ago.
It's hooked to the poles on the fuse panel under the hood and to a white wire on the ignition switch connector
Expert:  Jerry Newton replied 1 year ago.

Can you unplug the controller AT the controller? Just disconnect the controller itself from the wiring.

It may or may not net results. The idea here is to look at really quick and easy possible solutions, and this is one that stands out for me, due to the fact that the BRAKE fuse is one of the circuits affected. If I just unplugged the controller and nothing changed, I'd be satisfied that it's not the controller that's at fault.

Customer: replied 1 year ago.
Un hooked and still the same
Expert:  Jerry Newton replied 1 year ago.

OK, that's fine then.

The crux of this is that you now need to find out where the short to power is on this circuit. There's a lot to this circuit, it goes from the front to the back of the truck, so you'll have to start by looking at the easiest to access or most likely sources. I would get to splice S206, break that apart, and see which branch has the power on it, that will isolate a good chunk of the circuit right there. The most that we know about S206 is that it's in the IP harness about 6 inches away from the steering column harness breakout, so you'll have to put your hands on that wiring and simply start taking it apart to find this splice.

There's not an easy way to do this, but the root cause is a short to power on this circuit, there is no question about that.