Anyone know why air comes through the defogger vents at speed when the AC is off?
- Thread starter Rexxenexx
- Start date
jjorgensen52
NHSTE - I'm the only one!
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
it may just be the fresh air draw thing... designed to keep you from getting CO poisoning by drawing some air into the car. FWIW.
it may just be the fresh air draw thing... designed to keep you from getting CO poisoning by drawing some air into the car. FWIW.
jjorgensen52
NHSTE - I'm the only one!
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
who knows
who knows
Rexxenexx
Active member
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
The Ty does idle like it has a vac leak. Stumbling but doesn't stall. I'm checking the vac lines now but I dont see any that have a chance of leaking. I redid most of the lines and tied/clamped most of the ends. In D at a stoplight the vac jumps between #20-18.
I see the vac line going to the bottom vents. I pulled it (after the car was parked for 40min) and it did have vac in it. How is the top controlled? I dont see any lines going to it, I just followed the line behind the dist. that goes through the firewall and to the bottom vents.
The Ty does idle like it has a vac leak. Stumbling but doesn't stall. I'm checking the vac lines now but I dont see any that have a chance of leaking. I redid most of the lines and tied/clamped most of the ends. In D at a stoplight the vac jumps between #20-18.
I see the vac line going to the bottom vents. I pulled it (after the car was parked for 40min) and it did have vac in it. How is the top controlled? I dont see any lines going to it, I just followed the line behind the dist. that goes through the firewall and to the bottom vents.
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
This might have something to do with the vacuum actuated flapper on the passengers side under the windshield wiper grill....may be stuck open letting air in when you're moving....
I think that lets fresh air in when the A/C is on normal....then it closes to recirculate the cab air when on Max A/C... also, it should close when you turn the a/c off....check the vac ports behind the HVAC controls or pop the wiper grill and start your testing there....
This might have something to do with the vacuum actuated flapper on the passengers side under the windshield wiper grill....may be stuck open letting air in when you're moving....
I think that lets fresh air in when the A/C is on normal....then it closes to recirculate the cab air when on Max A/C... also, it should close when you turn the a/c off....check the vac ports behind the HVAC controls or pop the wiper grill and start your testing there....
Rexxenexx
Active member
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
For sure thats the prob. I went 90+mph on the 405 and felt air blowing out the top vents, I then turned the fan to low and turned MAX AC on and it closed. Its annoying as hell, like theres no windshield. So how can I make it close when the AC is off?
For sure thats the prob. I went 90+mph on the 405 and felt air blowing out the top vents, I then turned the fan to low and turned MAX AC on and it closed. Its annoying as hell, like theres no windshield. So how can I make it close when the AC is off?
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
I don't know how to fix it, just know how the flap is supposed to work....There's a network of plastic vac lines behind the dash that you could look at....perhaps one of them popped out and isn't doing what it's supposed to when you turn off the a/c....A vacuum needs to be pulled on the diaphram in order to close the flap....your not getting vac. there when it needs it....remove the hvac controls and look for a vac line that popped out behind there...There also might be some under the driver's side dash and by the ecm...any hissing under the dash when the a/c is off?
I don't know how to fix it, just know how the flap is supposed to work....There's a network of plastic vac lines behind the dash that you could look at....perhaps one of them popped out and isn't doing what it's supposed to when you turn off the a/c....A vacuum needs to be pulled on the diaphram in order to close the flap....your not getting vac. there when it needs it....remove the hvac controls and look for a vac line that popped out behind there...There also might be some under the driver's side dash and by the ecm...any hissing under the dash when the a/c is off?
Rexxenexx
Active member
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
Yea there is a hiss when you turn it off. I looked at the vac junction just behind the vent under the steering column. It looks like all are in. I could see the valve that activates when the AC is MAX. With the car off I watched it open when AC is MAX and close when I turned the AC off and you can hear the leak. So thanks guys for the help.
Now time to fix it. The leak is somewhere RIGHT behind the controls but I can only pull the controls 1.5" out and something is holding it, I see some slack in everything, but I can't get a good look at the large switch area.
I'll update this as I go so people w/ a similar problem could get an idea whats involved.
Yea there is a hiss when you turn it off. I looked at the vac junction just behind the vent under the steering column. It looks like all are in. I could see the valve that activates when the AC is MAX. With the car off I watched it open when AC is MAX and close when I turned the AC off and you can hear the leak. So thanks guys for the help.
Now time to fix it. The leak is somewhere RIGHT behind the controls but I can only pull the controls 1.5" out and something is holding it, I see some slack in everything, but I can't get a good look at the large switch area.
I'll update this as I go so people w/ a similar problem could get an idea whats involved.
blk00z28
Forced to by choice
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
Are you talking about the little slector valve thats leaking?
To pull the AC controls out you'll have to take the face plate off. Its alot easier to take it off and replace the little valve (if this is what's causing this leak. Mine did the hiss and only was able to use the floor and def. when it was on.). I think the valve is like $14 thru a dealer. :roll: I tryed everything on my stock one, from swelling up the little ruber that they use as the valve, or a shim, nothing worked. So I had to get a new one. :roll: (it seperates and cause's the leak.)
Are you talking about the little slector valve thats leaking?
To pull the AC controls out you'll have to take the face plate off. Its alot easier to take it off and replace the little valve (if this is what's causing this leak. Mine did the hiss and only was able to use the floor and def. when it was on.). I think the valve is like $14 thru a dealer. :roll: I tryed everything on my stock one, from swelling up the little ruber that they use as the valve, or a shim, nothing worked. So I had to get a new one. :roll: (it seperates and cause's the leak.)
Christian Dionne
Member
Re: Anyone know why air comes through the defogger vents at speed when the AC is off?
I think it's supposed to be open to outside air at all times, except of course MAX. All my S/T trucks have been this way, even with brand new selector valves. Usually it will blow top and bottom on the off position, unless you ziptie the vacuum actuator under the dash in low cash situations
I think it's supposed to be open to outside air at all times, except of course MAX. All my S/T trucks have been this way, even with brand new selector valves. Usually it will blow top and bottom on the off position, unless you ziptie the vacuum actuator under the dash in low cash situations