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Air out of dash and feet only #4490261
08/16/17 02:15 PM
08/16/17 02:15 PM
Joined: Sep 2013
Posts: 10,683
Indiana
dlundblad Offline OP
dlundblad  Offline OP
Joined: Sep 2013
Posts: 10,683
Indiana
On my Chevy blazer.

It looks like it's all vacuum actuated. I believe it may be the AC/ heater control switch. Even with the dial turned to off, a bit of air still comes in at the feet when the vehicle is cruising at highway speeds. I just need to take the trim on the dash out so I can get to it. The lines are small so checking it may be difficult.

Rock Auto has the part for $140 shipped. Anyone have any cheaper alternatives? There's always junkyards, but how do I know the one I pull isn't faulty either?


03 Jeep WJ 4.0 202k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 186k M1 0w40 Mahle OX149D
97 Chevy Blazer 4.3 153k Synpower 5w30 Supertech ST3980 (Ecore)

Re: Air out of dash and feet only [Re: dlundblad] #4490264
08/16/17 02:19 PM
08/16/17 02:19 PM
Joined: Sep 2007
Posts: 1,023
TX, USA
JMJNet Offline
JMJNet  Offline
Joined: Sep 2007
Posts: 1,023
TX, USA
Sometimes it is the motor.

The gear inside is cracked.


  • 2017 Toyota Sienna
  • 1995 GMC Suburban 6.5L Turbo Diesel


Re: Air out of dash and feet only [Re: dlundblad] #4490266
08/16/17 02:21 PM
08/16/17 02:21 PM
Joined: Aug 2008
Posts: 340
NJ
Padawan Offline
Padawan  Offline
Joined: Aug 2008
Posts: 340
NJ
Does this happen even when the system is set to recirculate? Did it only recently start?

All of our vehicles in recent memory have allowed some air in through the vents at speed unless set to recirculate.

Re: Air out of dash and feet only [Re: Padawan] #4490271
08/16/17 02:28 PM
08/16/17 02:28 PM
Joined: Sep 2013
Posts: 10,683
Indiana
dlundblad Offline OP
dlundblad  Offline OP
Joined: Sep 2013
Posts: 10,683
Indiana
No re circulation.


03 Jeep WJ 4.0 202k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 186k M1 0w40 Mahle OX149D
97 Chevy Blazer 4.3 153k Synpower 5w30 Supertech ST3980 (Ecore)

Re: Air out of dash and feet only [Re: JMJNet] #4490272
08/16/17 02:29 PM
08/16/17 02:29 PM
Joined: Sep 2013
Posts: 10,683
Indiana
dlundblad Offline OP
dlundblad  Offline OP
Joined: Sep 2013
Posts: 10,683
Indiana
Originally Posted By: JMJNet
Sometimes it is the motor.

The gear inside is cracked.


Pardon my ignorance, but what motor? smile


03 Jeep WJ 4.0 202k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 186k M1 0w40 Mahle OX149D
97 Chevy Blazer 4.3 153k Synpower 5w30 Supertech ST3980 (Ecore)

Re: Air out of dash and feet only [Re: dlundblad] #4490273
08/16/17 02:29 PM
08/16/17 02:29 PM
Joined: Jul 2017
Posts: 43
Vermont
John_VT Offline
John_VT  Offline
Joined: Jul 2017
Posts: 43
Vermont
Won't go to defrost? I've had the rod pop off on my suburban.


14 crosstrek 5 spd.Milesyn sxr 0-20
98 k1500 suburban 5.7L.Milesyn sb 5-30
03 Pontiac Montana. St 5-30
01 mojave,86 trx350,2-110cc atv's
Re: Air out of dash and feet only [Re: John_VT] #4490274
08/16/17 02:31 PM
08/16/17 02:31 PM
Joined: Sep 2013
Posts: 10,683
Indiana
dlundblad Offline OP
dlundblad  Offline OP
Joined: Sep 2013
Posts: 10,683
Indiana
Originally Posted By: John_VT
Won't go to defrost? I've had the rod pop off on my suburban.


I said dash, but I should have said defrost.

From what I've read, going to defrost and feet is a safety feature so you can still drive (and see) when whatever vacuum component fails.


03 Jeep WJ 4.0 202k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 186k M1 0w40 Mahle OX149D
97 Chevy Blazer 4.3 153k Synpower 5w30 Supertech ST3980 (Ecore)

Re: Air out of dash and feet only [Re: dlundblad] #4490376
08/16/17 04:37 PM
08/16/17 04:37 PM
Joined: Sep 2015
Posts: 1,595
USA
mk378 Offline
mk378  Offline
Joined: Sep 2015
Posts: 1,595
USA
It is almost certainly electric. By 1997 vacuum controls were obsolete.

If you turn the key on and don't start (so there's no engine noise) and push buttons on the control panel, do you hear gears grinding?

Re: Air out of dash and feet only [Re: dlundblad] #4490441
08/16/17 05:50 PM
08/16/17 05:50 PM
Joined: Oct 2011
Posts: 5,091
USA
NHGUY Offline
NHGUY  Offline
Joined: Oct 2011
Posts: 5,091
USA
Google "Mode door actuator".

Re: Air out of dash and feet only [Re: dlundblad] #4490496
08/16/17 06:55 PM
08/16/17 06:55 PM
Joined: Sep 2005
Posts: 5,910
MIchigan
Warstud Offline
Warstud  Offline
Joined: Sep 2005
Posts: 5,910
MIchigan
Originally Posted By: dlundblad
Even with the dial turned to off, a bit of air still comes in at the feet when the vehicle is cruising at highway speeds.

That's normal for GM vehicles.

Re: Air out of dash and feet only [Re: Warstud] #4490515
08/16/17 07:09 PM
08/16/17 07:09 PM
Joined: Nov 2008
Posts: 9,288
Phoenix
dishdude Offline
dishdude  Offline
Joined: Nov 2008
Posts: 9,288
Phoenix
Originally Posted By: Warstud
Originally Posted By: dlundblad
Even with the dial turned to off, a bit of air still comes in at the feet when the vehicle is cruising at highway speeds.

That's normal for GM vehicles.


Yes. Off on these vehicles defaults to floor and fresh air allowing air to flow through the system without the fan to prevent the air in the vehicle from getting stale.


2018 Challenger SRT 392 PUP 0w-40 Wix 57899XP
2018 GTI
Re: Air out of dash and feet only [Re: dlundblad] #4490580
08/16/17 08:17 PM
08/16/17 08:17 PM
Joined: Dec 2013
Posts: 2,449
Fort Worth, Texas
clinebarger Offline
clinebarger  Offline
Joined: Dec 2013
Posts: 2,449
Fort Worth, Texas
The lower Mode Door has "Minimum Flow Holes" that allows air flow from the outside with the system off, The Temperature Blend Door will still regulate the air temp.

All Air Mode doors are Vacuum operated.
The Temperature Blend Door is control by a electric actuator.

If you lose Mode functions.....Check the Vacuum line from the engine to the Vacuum Storage Canister, Check Valve, And the Vacuum line between the canister & firewall. The rubber lines under the hood will rot right off these trucks.
The interior vacuum harness is very reliable as are the mode actuators & switching valve.



2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/U341E
2000 Toyota Avalon 1MZ-FE/A541E
Re: Air out of dash and feet only [Re: mk378] #4490597
08/16/17 08:48 PM
08/16/17 08:48 PM
Joined: Dec 2013
Posts: 2,449
Fort Worth, Texas
clinebarger Offline
clinebarger  Offline
Joined: Dec 2013
Posts: 2,449
Fort Worth, Texas
Originally Posted By: mk378
It is almost certainly electric. By 1997 vacuum controls were obsolete.

If you turn the key on and don't start (so there's no engine noise) and push buttons on the control panel, do you hear gears grinding?


It really depends on what vehicle your reffering to....

My 2001 Camaro is Vacuum controlled Mode Doors, And Cable controlled Temp Door....Probably the most reliable HVAC control set-up.
A lot of the Subcompact cars still use cables to control all the door functions besides the Recirculation Door which is a simple Bi-Directional electric motor.
The OP's Blazer has Vacuum controlled Mode Doors, And Electronic Step Motor controlled Temp Door.

The 100% Electronic Step Motor controlled systems are the most common today & in my opinion is the least reliable control system.....But folks got to have their fully automatic dual zone temp control!!


2001 Chevy Camaro L92/4L80E
2006 Chevy 2500HD LBZ/Allison 1000
2010 Toyota Corolla 2ZR-FE/U341E
2000 Toyota Avalon 1MZ-FE/A541E
Re: Air out of dash and feet only [Re: clinebarger] #4491187
08/17/17 02:33 PM
08/17/17 02:33 PM
Joined: Sep 2013
Posts: 10,683
Indiana
dlundblad Offline OP
dlundblad  Offline OP
Joined: Sep 2013
Posts: 10,683
Indiana
Originally Posted By: clinebarger
The lower Mode Door has "Minimum Flow Holes" that allows air flow from the outside with the system off, The Temperature Blend Door will still regulate the air temp.

All Air Mode doors are Vacuum operated.
The Temperature Blend Door is control by a electric actuator.

If you lose Mode functions.....Check the Vacuum line from the engine to the Vacuum Storage Canister, Check Valve, And the Vacuum line between the canister & firewall. The rubber lines under the hood will rot right off these trucks.
The interior vacuum harness is very reliable as are the mode actuators & switching valve.



Good to know the interior harnesses are very reliable. Looks very tedious to work on.

The check valve is another possibility. I'll recheck my hoses, but I replaced them hoping they were the problem.


03 Jeep WJ 4.0 202k Castrol Edge 10w40 HM Fram XG16
02 Volvo S60 2.4T 186k M1 0w40 Mahle OX149D
97 Chevy Blazer 4.3 153k Synpower 5w30 Supertech ST3980 (Ecore)

Re: Air out of dash and feet only [Re: clinebarger] #4491193
08/17/17 02:40 PM
08/17/17 02:40 PM
Joined: Feb 2013
Posts: 3,340
Central Virginia
Silverado12 Offline
Silverado12  Offline
Joined: Feb 2013
Posts: 3,340
Central Virginia
Originally Posted By: clinebarger
Originally Posted By: mk378
It is almost certainly electric. By 1997 vacuum controls were obsolete.

If you turn the key on and don't start (so there's no engine noise) and push buttons on the control panel, do you hear gears grinding?


It really depends on what vehicle your reffering to....

My 2001 Camaro is Vacuum controlled Mode Doors, And Cable controlled Temp Door....Probably the most reliable HVAC control set-up.
A lot of the Subcompact cars still use cables to control all the door functions besides the Recirculation Door which is a simple Bi-Directional electric motor.
The OP's Blazer has Vacuum controlled Mode Doors, And Electronic Step Motor controlled Temp Door.

The 100% Electronic Step Motor controlled systems are the most common today & in my opinion is the least reliable control system.....But folks got to have their fully automatic dual zone temp control!!


Totally agree. I've replaced a blend door on my 2010 Mustang. Not only is it a PITA but one would think they should last longer than they do.


12 Chevy Silverado ext. cab LS, 2WD 4.3 auto
18 Mustang GT 5.0 auto
07 Harley Dyna Street Bob 96 c.i. 6 sp.
00 Mustang GT auto

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