98 4 door 4wd tahoe..have a few questions

[Lawrence0485]

Hey guys I just got this tahoe and I'm new these newer rigs lol.

On the hvac system. The know that switches from defrost, front vents, floor vents. When I try to select one it just blows air out of the defrost and front vents. Now from what I understand this truck is new enough that the hvac stuff doesn't run on vacuum like the older ones and it is electric. I looks like I need to replace the switch panel in the dash to make it work correctly?

Anyone have and experience with this?

 

[Larry]

Anytime there is a failure in the HVAC system the failsafe is to default to defrost. The issue could very well be a control head but chances are the issue actually lays with one of the two little mode actuators. I’ve been burned twice by going after a control head in GMT400 trucks only to have the issue turned out to be one of the actuators. The bad thing is there isn't a real easy way to determine which actuator motor failed so you pretty much have to replace them both. At the age of the truck replacing these isn't a bad idea anyway.

Below is what the actuators look like. There is one on the HVAC box near your gas pedal foot then another on the passenger’s side up under the dash. The one by the driver’s side is easier to change. I would start with that one first.

 

[Lawrence0485]

Great thanks I'll look into that. I'm working fixing this rig up and keeping it for a while so it not a big deal to replace a few parts.

I know If I have the recirculation button on, I can hear the flap close randomly every 30 sec or so. What do you think about that?

 

[Larry]

Great thanks I'll look into that. I'm working fixing this rig up and keeping it for a while so it not a big deal to replace a few parts.

I know If I have the recirculation button on, I can hear the flap close randomly every 30 sec or so. What do you think about that?

I still think it is more of a blend door issue due to an actuator problem. That is where I would start anyway just because I've seen the actuators do this same thing before.

 

[Lawrence0485]

Ok cool I'll get some actuators ordered.

 

[Lawrence0485]

What does the one by the gas pedal control?
The one up under the dash?

Now when I turn the temp knob, it does work hot to cold like it should

 

[Larry]

I can't remember which one does what but if one of them is defective the entire system will not work properly and default into defrost. One of the actuators will control air flow and the other is temperature. As I mentioned, it is very difficult to diagnose those so just replace them both.

 

[Lawrence0485]

Gotcha will do. Thx

 

[bigblock72]

Look on the heater box above the throttle pedal and make sure all of the links are still attached to the mechanisms that connect the actuator to the door levers. These are notorious for falling off randomly and causing what you describe.