A/C heater vent not blowing front dash

[ahm_3333]

I'm new and need some help. I have an 82 gmc 1/2 that I cannot fix, it blows a/c and heat from below under the dash strong, but blows very little in the vents that are in the dash for some reason, does anyone know what it could be.....help....

Thanks
AD....

[Prong]

It's probably the blend door in the heater box under the dash (below the glovebox), or you have arotted or disconnected vacuum line to an actuator that controls the air flow.

[ahm_3333]

Thanks for your input

[motornut]

hi just above the gas pedal make sure there is a vac line on the (floor to defrost)diaphram,and on the pass side remove the duct work to access and check if this clip is broke door won't work to close vents

[ahm_3333]

Thanks for the info.....

AD......

[kevinr1970]

Originally Posted by motornut

hi just above the gas pedal make sure there is a vac line on the (floor to defrost)diaphram,and on the pass side remove the duct work to access and check if this clip is broke door won't work to close vents

My problem in my '82 is that when I swtch it over to defrost, it barely comes up through the top vents but seems to all come out through the front vents. When on heater it seems fine on the floor.
Should I be looking at the same thing?

Any place I can look that explains the mechanics of how the HVAC system works?

[Justins76]

I have that same problem and it turned out to be the plastic part broken just like in the pic above. Does anyone know where to buy a replacement part?

[dswancutt]

They are still available from GM. I bought a whole package of 5 on 12/10/09. The part number is 3018715 and they list for $2.25 each. I just bought the whole package so I have some spares for the other trucks.
Hope this helps.

[Justins76]

Thanks for the part #

[jdclemons]

Hi guys im new and i ran across this post and im having a similar problem. My heater/ac blows buts it comes out in both places defrost and front vents at the same time. I replaced that clip shown in the picture above but it seems like i have no vacuum. I have a 1987 silverado efi throttle body. Can anyone tell me exactly where it gets its vacuum from.

[jpenny376]

Hey motornut can u move that bundle of wires and get a pic of that top part? The person who had my truck before me decided to take the springs and that rod with the screw end off. I guess they did not pay attention to how they took it apart cuz it was just laying on top.

[RandyP]

Hang on, he has to get the runway cleared so he can reach 88mph!

[motornut]

a little from the side?

[jpenny376]

Little more left??? Other end of that rod plz

[motornut]

Originally Posted by jpenny376

Little more left??? Other end of that rod plz

sorry didn't get any that way

[jpenny376]

Darn.....thanks anyway

[jpenny376]

any idea where to get a look at it???

[motornut]

no sorry the jimmys don't have AC
and that truck is about an hour away
going for scrap soon....

[jpenny376]

ok thanks

[72freak]

I had the same issue. Mine was the small hard plastic vacuum line coming through the firewall next to the heater box in the engine bay.. It had been broken and not repaired. No vacuum was getting to the control unit to make the switch happen.

[jpenny376]

Figured it out. The vacuum line was hooked up to the wrong place. It was on the carburator where it was not getting constant vacuum. Moved it to manifold and it works great now. Thanks for the help. Vacuum problems are a pain in the rear.