2002 Defrost Only/Little Heat

[Rob.D]

I've got an 2002 XLT 4.6L with 136,000 miles. It's my wifes daily driver and this week the heat controls started acting up. All fan speeds work correctly but the only place it will blow air is through the defrost vents. Also the heat is not very warm at all. I've done some searching and there is a vent of some kind that will make a clicking sound when you go from hot to cold if faulty. I'm not hearing a clicking sound at all. The temp gauge on the dash reads normal. Any suggestions?


Head to the Upper Penninsula to do some snowmobiling wont be able to read post till I return on Sunday. Thanks

 

[bhults]

I had a similar issue with my 95' EB... I have the electronic climate control in my rig, not sure if you have that, or the knobs. In my case, it turned out to be a vacuum issue - there was a cracked line or something, that prevented the system from redirecting air flow to the desired selection. By default, the system will route air to the defrost vents when it incurs a problem like this (to ensure you can SEE out the windshield). I couldn't make much sense out of the multicolored vacuum lines, so I had my local mechanic repair it. It was a long time ago, but from what I remember, it was a relatively inexpensive fix. As for you're temp problem, I'd investigate your thermostat first... It may be running open, in which case you won't get much heat. Have your heater-core checked next.

 

[matt0248]

There is a heater control valve in the engine comartment that controls the flow of hot coolant into the heater core. it is vacuum controlled. This could have failed, or there could be other vacuum leaks in the hvac system. On my explorer the "mode" blend door, i.e. defrost, floor, or vent, is vacuum controlled also. You may just have a vacuum leak.

 

[Rob.D]

What's the best way to determine a vacuum leak? Visual?


Also I have manual controls for all hvac functions.

 

[matt0248]

You may hear a whistling noise or a slight hissing noise from inside the dash area, ot outisde under the hood. Usually there is a crude vacuum diagram under the hood somewhere.

 

[bhults]

I don't think it makes a difference whether your controls are electronic or manual since both systems rely on vacuum to get the job done. I, at first, thought my blend door motor was shot too, but it wasn't.

I really don't know how to check for a vacuum leak; that's why I went to my mechanic. If you're hell bent on finding it yourself (which is admirable!), I'm sure you can find the answer if you scour the forums a little deeper.

 

[Rob.D]

Hopefully have a little time to check for vacuum leak this week after work. Thanks for all the suggestions.