98 Chevy heater controls location.

I am having problems with my heater not changing locations (ie; defroster, dash and floor), it basically stays on the defroster but it also moves from dash and floor. In short, the defroster stays on, but the dash and floor shut off and turn on when they are sapposed to.

I have no idea where the controls are for the directional air flow.

If one of you guys (or girls!) could get me in the right direction so that I can figure out if it needs to have the solinoid replaced or just get it unstuck.

Thanks, Gary

All of the controls are in the evaporator box under the glove box. You might have pull the box if the damper (mode door positioner) is broken.

Do you think that would be what it is?

You said that it is behind the glovebox? The reason that I ask is because I had the dash pulled back to get to the passenger airbag. So I may have messed it up.

The vacuum actuator for mode is on the LH side of center on a GMT400, right NITROUS? The temp and recirc actuators are electric but I'm pretty sure the mode actuator(s) are vacuum. Make sure the vacuum source from the engine is OK too.

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Originally Posted by GasGuzzler

The vacuum actuator for mode is on the LH side of center on a GMT400, right NITROUS? The temp and recirc actuators are electric but I'm pretty sure the mode actuator(s) are vacuum. Make sure the vacuum source from the engine is OK too.

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Correct Gas Guzzler.....

I would start looking at the wiring to make sure something hasn't been pulled off. Some of the connectors are hard to see so look closely.

I tore into it last night and found that the butterfly that shuts off the defroster was out of its position so it was just flopping around in the housing. I also lubed it up while I was in there.

On another note, I am wondering if you guys have figured out a way to fix the fan control switch's 4th position. It is the position right before high. (medium-high) I have replaced the switch twice and it works for about a month and then it quits. The rest of the positions work, but only that one quits. I have broke down the switch and the terminal bends everytime. I just put a piece of plastic under the terminal to see if that would help to keep it from bending, but that didn't work. So does anybody know how to fix it permenantly so I can use that speed on the fan?

Would soldering the terminal work? Or do I have to do something else?

These trucks are good for burning up that connector. You can get a new pigtail at the dealer if the terminals are fried or the plastic is melted or brittle.

The resistor for the speeds is behind the glove box on top of the AC case. They have trouble some times too. Also make sure the blower motor ground is good.

Like I said it was just the flapper that shuts off the air to the defroster.

I checked all of the solonoids and they were working good. Just that one vent block thing!

I ended up following all of the piping from the passenger side of under the dash.

I've found that the motor will cause your problem with blower speed also. Check the motor connector (I believe the red wire) and see if it's started melting or gets hot when running. You can try tapping the motor when the switch is in the 4th position and if it starts, replace the motor. I hope you cleaned the evaporator real good when you opened the box up because you'll lose air flow from all of the outside trash that gets in it.

What are you talking about being cleaned, I went in from the center by the floorboard inside the cab. I didn't see anything that would need to be cleaned.

Please elaborate!

I've seen some people pull the blower motor out when they mess with the positioner eventhough it doesn't need to come out. If you pull it vacuum out the inlet hole directly to the left to get more air flow. I should have give more detail.

No, I didn't pull the blower motor. But thanks for the tip incase I ever do need to pull it out.

The only problem I had with fixing this was getting my hand in the hole to position the flapper. My hand has a nice bruse on the back of it now! I guess I should have had my wife help at that point.

The power wire to the blower is purple.

These trucks typically break the plastic on the bottom of the case that prevents foreign objects from entering the motor. If you throw lots of wrappers and trash in the passenger floor, the stuff gets sucked into the motor and causes it to make lots of noise without much airflow.

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Originally Posted by GasGuzzler

The power wire to the blower is purple.

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Agreed, it's just a spade connector but there's a connector with a black and red wire (I believe) that get's hot and melts. If you unplug it I'm pretty sure the blower will quit but I can't remember without looking. I know it goes through the firewall If you have to pull the harness.

Now here is the issue. That d@mn air valve came off again. Now it is just flopping around in the housing.

I was wondering if there is a clip that holds it in place or if it is sapposed to just sit there in the opposing hole?

If not where does the clip go? Near the arm, or on the opposite side?

This REALLY pissed me off this morning!

I finally fixed the problem, I built a little arm out of plastic to keep the control arm from being able to back out. Just screwed it into the side of the airbox.

So this is done.