Hi! This is my first post in hopes I can find an answer and solution to a heating problem. My '02 4X4 LS heating system duct for the Floor mode has failed. When the switch is positioned at Defrost or Face vents, they're fine (nice and toasty), however, when I switch to Floor, the system goes to defrost.

Anyone know:

1. What's causing this; and

2. What the solution could be?

I checked the switch and noticed all vaccum tubes were intact. But have no idea where to even start looking for the actuators as I think this might be the culprit or a vaccum tube came off.

Any help will be greatly appreciated....

Thanks

lcars [&o]

 

I have a similiar prob. 97 blazer. Heat blows outta defrost vents only. It does blow hot. I searched and am confused on if its main vac line or individual ones?? Where is main vac line?

 

It is most likely the main vacuum line. The vacuum line is black and about the size of a pencil. It will come from a tree/fitting on top of the engine, behind the intake and will go to the cowl on the drivers side. It may go to a vacuum canister before going to the cowl, depending on the year.

You will need to pull one end off and cut about 1 inch of it off the line. Take that to your parts store and buy 3-4 feet of it. Eye ball the distance, should be close. You probably will not be able to see the tree/fitting that the vacuum line is plugged into, behind the intake. Trace it from the cowl or vacuum canister to the engine. Feel where it plugs in and pull it off. Most likely, no clamps on the line. May be stuck or break off at the fitting. If it does, you may need a knife to remove the rubber from the tree/fitting. Have the new line ready and plug it in.....route the line along the path of the old one, to the firewall/canister and plug it in. Some lines may vary in size. The main line may be one size and a small piece at the firewall may be slightly smaller. Once the line/lines are replaced, the vents should now work.

 

Sorry tdannar, but I'd have to disagree with you. If the defrost and the dash vents work, then the vacuum supply is working. I would have to verify that the switch is applying the vacuum to the proper ports. I'll try to locate a post I made awhile ago as to the schematics of the HVAC vacuum system.

 

Here's the thread where I posted this information: Heater issues - Help I just...

It most likely is the mode actuator line either being cracked or the actuator bellows is cracked.

 

I found this post once, but it doesn't tell me where to locate these parts. The Haynes manual doesn't even talk about the vacuum system except the actuator and switch in the transfer case system (less that's it).

 

After work today, if I remember, I'll try to get you a location on all of the actuators.

 

The vacuum lines run to the back of the switch on the dash. As you move the lever to change which duct you want to have the air come out of, the flow of the vacuum changes. There is a round looking thing with about 6 or so colored vacuum lines attached to teh back/side of the switch. Carefull if you remove that switch, if you force it and break that connector you will have to buy a new switch. All the vacuum hoses run behind the stereo. If you installed a aftermarket head unit, you may have accidently pinched one of the hoses, thus causeing your problem.