always on defrost?


mobrule
07-02-2004, 04:26 PM
Hi,

I just replaced my blower motor in my 95 jimmy.

When i put the switch on a/c, air only comes out of the defrost vent.
Air only comes out right infront of the windshield and by my feet.

It does this no matter what its set on (vent, a/c, defrost, Bi-Lev).

Any ideas?

Ive tried two used interior control panels.....they are all doing it.

thanks.

mobrule
07-04-2004, 10:49 AM
Does anyone have any suggestions?

GMCTech
07-05-2004, 08:05 AM
Sounds like you have a broken mode door.

The mode door can be checked. At the driver's feet on the right side you can see the heater box (ventilation case). About 3/4 of the way up towards the firewall there is a plastic tab sticking out through the box that is hooked to an actuator.

Switch the controls from A/C to defrost and watch the movement. If it is broken only the actuator will move but not the rest of the plastic door.

Reach up and move it around. If it broken you won't be able to move it too much, only a little. If it is broken it will "rattle" around while you are trying to move it.

Check that first. By the way, we have replaced a few of these, and it is not too uncommon.

Hope this helps.

mobrule
07-05-2004, 11:11 AM
Thanks, I'll check that out today.

I was thinking maybe the little vacuum lines that go into the back of the a/c defrost switch arent doing what they are supposed to.

Everything was fine until i replaced the blower motor.

BobcatAZ
07-06-2004, 10:12 AM
I just go through replacing the heater/defrost door on my Ď98 Jimmy. Had to remove the whole dash from the vehicle. :banghead: Sounds like a major job but it wasnít too bad.
I then removed the broken door and glued it back together and added some reinforcement at the brake.
Cost?: My time and a little glue. :grinno:
If you get into this project Iíll try and remember what did and didnít need removel.
Hope this helps.

mobrule
07-06-2004, 11:23 AM
I Looked all over for the mode door but couldnt find it????


I would be surprised if it is the heater/defrost door because it was working fine until took out the blower motor and disconnected the switch panel from my dash.

But its getting hotter and hotter by the day so im willing to try anything!

shrkarx2
07-07-2004, 06:36 AM
Try this, Put it on vent and observe ths a/c compressor. If it is running it is a problem with switching/wiring (during blower motor replacement) the truck thinks you want defrost. If the compressor isn't running it is a problem with the mode door or actuator. Note the a/c runs in defrost mode to provide dry air for defogging.

mobrule
07-07-2004, 09:40 AM
thanks that makes sense.

Im pretty sure the a/c kicks on when i put it on the a/c options and not when it is on vent.

But the blower motor has died again..... i should have put in the new one but after a bench test i thought my old one was still working.


so if it is a wiring /switch problem do you know what to look at first? I tried 2 different switch panels...but they both did the same thing.

mobrule
07-07-2004, 11:44 AM
just installed a *new* blower motor..

as i suspected the compressor kicks on when its supposed to.

any suggestions on a easy way to get at the mode door or actuator in a 95 with 4wd?

BobcatAZ
07-07-2004, 12:47 PM
just installed a *new* blower motor..

as i suspected the compressor kicks on when its supposed to.

any suggestions on a easy way to get at the mode door or actuator in a 95 with 4wd?

Donít know about ĒEasyĒ and I donít know if the dash of a Ď95 comes out like a Ď98? Maybe GMCtech can advise. If your dash is like my Ď98 I might be able to help some.
However, right now Iím kinda busy watching the Nuttal and Gibson Fire in southeast Arizona come together in the canyon above my house. Anyone got any extra water hose????? :iceslolan

mobrule
07-07-2004, 01:35 PM
i took off all the plastic at the bottom of my dash (near the drivers feet) and i found what i believe to be the "mode door".

With the switch on vent air blows through to the mode door... if i push the door up air rushes at the windshield vent, and if i pull it down it just comes out at the feet vents.

The door doesnt move when i switch through a/c or defrost unless i push or pull the door manually.

Could it be the actuator? Or could it be a loose vacuum hose somewhere? A Hidden fuse?

mobrule
07-07-2004, 03:45 PM
anyone know of a diagram that shows where the little colored vacuum hoses go. (the ones that go to a/c, vent, defrost, blend) ive found a blue one floating around but have no clue where it goes to....

BobcatAZ
07-07-2004, 09:27 PM
anyone know of a diagram that shows where the little colored vacuum hoses go. (the ones that go to a/c, vent, defrost, blend) ive found a blue one floating around but have no clue where it goes to....

I don't remember what color hoses go where but I believe that the defrost/heater door actuator has two hoses. The door should be spring-loaded to the "neutral" position. If you have a hand vacuum pump you could pull the HVAC control module (I know, "AGAIN!") and apply vacuum to each hose and watch the defrost actuator. Hope this helps. :uhoh:

joeval
07-07-2004, 09:37 PM
Sounds like it is a vacuum hose. They usually connect from the intake manifold to somewhere in the fan actuator. They are normally black about 1/8 inch thick. It may not be broken, but could be cracked and hard to see. Just look around for this size hose, there shouldn't be too many of them.

jdmccright
05-21-2006, 08:14 PM
I know this is a much later post, but I may as well throw in what I've found out. I have the same issue with my '96 Jimmy 4wd with the air not coming out of the dash vents. There are five little colored vacuum tubes that from the dash selector down into the bowels of the AC. Their function is as follows:

Grey - Vacuum supply to the AC
Orange - Routed to a door located on the passenger side, believed to select fresh or recirculated air since I can view it when laying facing up and see the door operating through holes in the housing.
Brown & Black - Operates the door located next to the driver's right foot. Spring-centered, this diverts air to the floor, the dash/defrost, or both.
Blue - Operates thd door located behind the radio. Spring-loaded to revert to defrost. The vacuum actuator is located just above the heater core on the passenger side.

Hope this bit of info might help anyone looking air conditioner vacuum tube color functions. Good luck!

(Edited 30-Jun-2006) I just replaced the vacuum actuators for both doors. The one for the dash vent/defrost door had a nice hole in the diaphragm so couldn't be salvaged. The other I replaced because it was sticking a little and since I had the dash apart for one, I might as well do both...each were $22 at the dealer. The top one was easy enough once you roll the dash forward on the bottom pins. The bottom one (next to the driver's right foot) was a PITA, requiring me to unbolt the gas pedal from the firewall so I could get clearance, cut about 1/4" off the door peg that the actuator's arm slips onto, and shortening one of the tabs that the actuator slides and snaps onto. Otherwise, I feared wrenching the new one too hard and tear the diaphragm inside in order to get it in place. But that said, all the doors work again and I have cool air just in time for summer!

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