Hvac gurus needed

The Dread Pirate Fisher

The Dread Pirate Fisher

Donating Member
Almost done with project. But hitting a wall, need some advice.

On the hvac selector, I can get hot or cold air, so I know the temp selector and door are working. My issue is the other selector where you decide where the air comes out of. Right now it will only come out the bottom and the defrost vents by the windshield.

I though it might be the selector so is got a new AC/delco part # 1571490 and installed it yesterday. To no avail I still cannot change the air routing.

What am I missing? Is there something else to check?
 
The Dread Pirate Fisher

The Dread Pirate Fisher

Donating Member
Re: Hvac gurus needed

I replaced the vacuum lines in the engine bay, and changed the vacuum ball with a new ac delco one. Is there an under dash vacuum schematic out there some where? I've not seen one and can't find one, just the engine bay one.

I know that there are those colored vacuum lines that come off the hvac selector but I don't know where they lead
 
sly dvl

sly dvl

Ya, it's got a Turbo
Re: Hvac gurus needed

Do you actually have vacuum at the selector? With no vacuum the system will default to Defrost for safety...
 
B

blackty

Active member
Re: Hvac gurus needed

Replace the actual selector behind switch. I believe default gives defrost and floor only. There is a good write up on this here. Be very careful when replacing to ensure proper adjustment. Look around, been covered...Jim
 
TNPhoon

TNPhoon

1of28
Re: Hvac gurus needed

Is it a silicone vac kit? Check the check valve going up to the HVAC. Mine was pre-installed backwards and I had the same issues. One day for the hell of it I pulled the check valve and realized it was backwards. Swapped it and vents worked just fine.

The one I am referring to is the top/left on the diagram:
vacuum_diagram.gif
 
The Dread Pirate Fisher

The Dread Pirate Fisher

Donating Member
Re: Hvac gurus needed

Ok so I think I found a possible source of the problem, I found a 3 prong check valve connecting the vacuum tank, cruise, and HVAC. The diagram only shows a 2 prong check valve then into a T fitting
 
The Dread Pirate Fisher

The Dread Pirate Fisher

Donating Member
Re: Hvac gurus needed

I everything is fine as in hooked up correctly, no change. So where else can I look? What's the big black diaphragm on the heater box near the driver side?
 
gstacky

gstacky

Member
Re: Hvac gurus needed

You need to verify that you have vacuum coming in to the switch, it's the small hard black line that goes through the firewall directly behind the distributor. If you take your radio out you may be able to access the back of your hvac panel and make sure that the vacuum plug there is on correctly too, and you should be able to hear the hiss when changing modes. You should triple check that check valve on your vac kit, to make sure it's installed the right way.
 
The Dread Pirate Fisher

The Dread Pirate Fisher

Donating Member
Re: Hvac gurus needed

All the rubber under dash lines are connected, I don't hear any hissing like there is a leak.

Can't find any diagrams with dash vacuum lines.

I confirmed that the check valves are in correctly, from what I can tell. They are drawing air towards the engine.

I can't follow that hard plastic engine line, I can't find it through the fire wall so I can't confirm it's ok
 
The Dread Pirate Fisher

The Dread Pirate Fisher

Donating Member
Re: Hvac gurus needed

Ok so I confirmed that I'm not getting vacuum to the colored rubber lines off the selector.

I CAN confirm the engine vacuum lines are correct.

I need some insight to where I can follow this hard line into the cab, do I have to remove the dash to access it?
 
gstacky

gstacky

Member
Re: Hvac gurus needed

Removing the dash gives you full access, you may be able to gain some access through the radio panel and by removing the HVAC controls. It is a pain to get out and you will likely break the keeper that holds the temp control cable in this way.
If you take the entire dash out it will be hard to test the system, so remove the radio and slide the HVAC control out some and see if you can see anything. The coloured hoses on the back of the HVAC have 2 small clips that hold that connector to the back of the control unit. They are push pins and you should be able to get them off with some small tools to pick at them.
 
The Dread Pirate Fisher

The Dread Pirate Fisher

Donating Member
Re: Hvac gurus needed

Yeah I've got the stereo out, and I pulled the HVAC control out as far as it will come, which is not very far.

What I need is to find where the hard line from the engine bay comes into the fire wall and check that to see any leaks, what odd is that I don't hear any hissing at all with the engine on, I can select hot or cold air, the bottom main vent door is stuck open,

Just odd
 
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