Defrost is on all the time not sure why.

CRF450R · Aug 29, 2019

So I noticed that my defrost is on all the time in my truck and it's driving me nuts. On the hot days specially after after some hard Moto's in the Saskatchewan heat I'd like all the ice cold air coming out of my front vents. It'll blow air out of the vents I want but it always is also blowing air out of the defrost and I find my a/c has to work overtime to cool off the cab. Any insight of what the problem is and how to fix it would be greatly appreciated. I'm really starting to hate my 98 Z71 seems like problem after problem after problem $8000 in recent maintenance work now this

df2x4 · Aug 29, 2019

It's almost certainly something with the blend door, or the door seal inside the box. Dash is going to have to come out to get to it. I've had this problem in my red truck before, was around $750 IIRC to have a shop replace the door. My Suburban has the same issue right now, I'm using a towel to prevent air from hitting the windshield when I'm not using the defroster until fixing it hits the top of the list.

Dubs · Aug 29, 2019

Make sure your blend door servo is working before you head the dash out.

bugdewde · Aug 29, 2019

Blend door inside the HVAC box behind the dash.
.... GMT400 are electric motor operated.

A lot of vehicles are vacuum operated and default to defrost when vacuum is lost (safety feature for visibility) via a spring.
Not sure if ours default to defrost since ours are electric. I've read a few threads on here concerning these doors, their motors and switches. Seems to be a common issue.
Do a search, there's probably a good write-up here with a fix.

deadbeat · Aug 29, 2019

You can tilt the dash down and not have to pull it. Basically, pull enough plastic to drop the steering column down, you don't have to remove it. There are a couple bolts inside the dash above the glove compartment that have to come out, and then one on each side by the kick panels. After this you can tilt the dash down and replace that blend door. The only downside to doing it this way is you can only put three(?) of the four clips back on IIRC. Actually, on another truck at this point I had to replace the evaporator so I simply moved the passenger side of the dash over and back and removed the whole air box without completely pulling the dash, although I'm sure I was just a couple wires away at this point but it was easier to leave it in for me.

CRF450R · Aug 29, 2019

Well f##k I guess the truck is going up for sale that's the last straw I'm think I'm done.

deadbeat · Aug 29, 2019

It literally took me about 1 hr to change the flap last the first time I did it.

deadbeat · Aug 29, 2019

https://www.gmt400.com/threads/deadbeats-1997-centurion-conversion.27953/page-8#post-914733

According to my post here I lied above, it says here it took 3 hours.

CRF450R · Aug 29, 2019

deadbeat said:
https://www.gmt400.com/threads/deadbeats-1997-centurion-conversion.27953/page-8#post-914733

According to my post here I lied above, it says here it took 3 hours.

Sounds like news I didn't want to here about I'm not sure if I'm interested in pulling a dash out of a truck. Im thinking it's maby just time to send this money pit down the road but we'll see that just might be my frustration talking to.

Dubs · Aug 29, 2019

It's your frustration.

Defrost is on all the time not sure why.

CRF450R

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deadbeat

Centurion Crew Cab

CRF450R

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deadbeat

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deadbeat

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