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HVAC Issue, Stuck on Defrost/Lower Only, Help

9

98GTPDaytona

New member
Hey guys, I'm Nick, new on this forum. Just recently picked up a 1998 Grand Prix Daytona 500 #1388, 133K, love the car, runs great, even better its that awesome blue color. I've been trying to track down an hvac issue, it seems to be stuck on defrost and lower foot. When I turn the blower motor on I can hear it blowing and changing speeds, so I don't think its the blower motor resistor. It won't blow out the forward vents, just barely out the defrost and lower foot vents. I have not tried the ac but have it on max heat and temp seems lukewarm. Checked vac lines by battery and is not corroded. So from what I've read, I'm thinking blend door actuator, and that's about as far as my troubleshooting has gone. Looking for input as far as where to go next. I'd be nice to have heat again. Thanks guys
 


I agree on the blend door problem, I would also follow the middle vacuum line off the supercharger vac tree, it leads down the firewall and into the cabin, so if that is off or broken.
 
That's the vac line I checked, followed it from that vac tee down through the harness and checked where it runs by the battery, no corrosion. Will double check it though. Would I be better off buying a new blend door or swapping a used one, or is there a way I can troubleshoot it first?
 
blend door? wouldn't it be a mode door vac module on the driver side under the dash? when u turn off the hvac do u hear a vac leak inside the car? this is the same thing mine did and it had a vac leak then I replace the val module or the thing under the first pic in that thread
 


what this guy said. ^^^^

the blend doors may be bad, (unrelated to the air flow) try the ac and watch them turn from hot to cold. via the post for the replacement.

we have a member here who also had it stuck on defrost and foot, the arm off the vac pump where it enters the hvac box broke. it was the d/s that was broke. if you take off all the stuff the thread tells you to you can move this arm and linkage, you'll know if its broke off or not.

moving this if its still hooked up and not broke, it should move the air flow. you may need to pull the vac line off the vac pump, the round part in the diagram.
 
00grandprixgtp said:
blend door? wouldn't it be a mode door vac module on the driver side under the dash? when u turn off the hvac do u hear a vac leak inside the car? this is the same thing mine did and it had a vac leak then I replace the val module or the thing under the first pic in that thread
Click to expand...
I haven't noticed a vac leak with the hvac off.. is the mode door vac module seperate from the blend door actuator? I'm gonna check into it this week.
 
the round part, bottom right of the pic is the vac pump. its has a vac line right to the center top. those linkage bars move the direction of air flow. you got one on both sides of the dash

the blend door actuator is the part to the left.
LH.gif
 
That vacuum line goes all the way into the driverside fender. If that vacuum ball is broken etc, you'll have it default in the positions you are getting.
 
BillBoost37 said:
That vacuum line goes all the way into the driverside fender. If that vacuum ball is broken etc, you'll have it default in the positions you are getting.
Click to expand...

Where's this vacuum ball located? I traced the line where it tee'd off the supercharger down by the battery to make sure it wasn't corroded. Didn't really look too much on the driver side.
 


that line goes across the front bumper to the d/s fender, under the air box. if you pull the fender plastic you can see it.
 
i have the same problem, but i have the automatic hvac, not sure if thats what you have or not.

with my hvac off, you can hear a rubberband sound like something is pumping, doesnt sound like a vac leak to me, like mentioned above. more of a pumping sound.

do you hear a sound like this? i feel like this sound i hear is the vac module the guy posted about above.
 


Ok so I brought the car to my job put it up on a lift. pulled the fender liner and airbox out and looked for the vacuum ball in the pic above, there's nothing there. No ball, no vacuum line, just empty space. I just checked it twice. Did all models come with these?? A little confused... The pic clearly shows where it should be...
 
Found this on a forum regarding the vacuum ball: "Mainly, it is used to provide a vacuum source to the HVAC system to control the actuators under the dash and keep vacuum up to accessories during low engine vacuum periods like when going up a long steep grade. Around '98 and up the ball reservoir under the fender was eliminated and the reservoir was moved to under the dashboard." Truth to this?
 
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