Heater only blows at floor

[Irishmic]

Hi guys, so I just got my heater up and running(ish) however it only blows out of the floor vents. Moving the switches does not change where it is coming out of. To be clear it seems as the heater blower needs to be swapped out as it has little pressure, enough to warm up the truck but want to be able to unfog the window.

Background, the heater did not work at all, turns out it was disconnected. So today I got it reconnected. Turning it from low, medium, high changes nothing. Switching it from vent, floor, defrost, changes nothing.

I am wondering if anyone has a good path to send me down, at least at this point I can warm up the car and remove the frost. I live in the northeast so am motivated to get this fixed. Thanks for taking the time to read my post.

 

[frankin5]

Vacuum operates a lot of this system. The blend door is cable operated and has a weak link in a plastic attachment. The blower motor has a relay on the side of the AC housing under the hood.

 

[Wes Harden]

These are for rpo c60, factory ac. the blower motor electric circuit will be the same for heater only truck. Does your truck have ac ?

So something is wrong inside your plenum, any failure of the vacuum system should default to the defrost only.

what year is your truck? there is temp blend door cable adjustment behind the glove box on the 73-80, not sure about the later models.
There may be an object blocking the doors in the plenum or possibly a vacuum pot is disconnected.

the hi blower relay function is to provide battery voltage to the blower. So with the fan switch on hi the relay should close and give full system voltage. Any other fan speed selection power passes through relay to resistor block, then back through relay to blower motor.

Orange wire on relay will be Hi fan signal if you supply battery voltage to the orange wire terminal, your blower motor should run full blast. If not the relay is bad. the dark blue wire is the return from the resister block and will have different voltage depending on fan switch position.

also there maybe a 1/2" gap between the lower plenum and the defrost ducts. I sealed mine with gorilla tape. The factory used foam, which falls apart after so many years. you might be leaking air flow in the dash.






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[kennyw]

Do you have heat only or heat and AC? There are two completely different systems depending on that answer. AC trucks use vacuum to switch between different positions (floor vs dash vs defrost) while heat only uses cables.

 

[Irishmic]

It is a 1980. It does have an ac unit in it but does not work. Seems it's just stuck on heat. Moving the switches nothing changes.

 

[Irishmic]

Also, moving it from low setting to high changes nothing.

 

[kennyw]

Then you have a vacuum issue. Start with making sure you have a vacuum line hooked up to the engine.

 

[Wes Harden]

Still with no vacuum at all the defrost should be the only place you get air flow. There is more wrong than the vacuum alone.

 

[Irishmic]

Still with no vacuum at all the defrost should be the only place you get air flow. There is more wrong than the vacuum alone.

As you said, the cables are behind the glove box. The temperature cable moves freely from dash controls but the vent selector from the dash does not move its cable inside the glove box. When I move from insde the glove box I can hear it changing and I can get a tiny change to the defrost but not much more then a trickle. Hopefully I'm making sense with my explanation

 

[Shawn]

Thanks for making this post. Great info @Wes Harden !

I'm having the same problem with my 89 Blazer. Can't get vents to work on AC. I bet its a vacuum line issue somewhere.

 

[Shawn]

Couple videos on the climate control vacuum switch and how to try to fix it on the cheap side.

 

[Wes Harden]

#22 in last attachment pic, is the heat defrost door. there is a long rectangular hole in bottom of plenum, over trans hump, for defrost mode the door #22 should be blocking this opening. you can feel with fingers. If it is, look just above there and see if there is a large gap between plenum and defrost duct work.
If you can't feel the door blocking the bottom opening, heater floor outlet, something is blocking the door or holding it open. with the truck totally off, no power, no vacuum, that door #22 should be blocking the floor heater opening.

edit fyi #16, behind glove box, should be rotated to toward the driver side of truck for winter, full heat.

 

[Irishmic]

I want to thank you all for the detailed help. I habe gotten progress but waiting on some parts, a new heater blower mainly.

The issue I habe at this point is the heater now seems to be running so hot that the floor vents are so hot to the touch I'm worried of fire. It's not blowing much just a little, why I'm getting a new blower. But as it is can the heater and everything cause a fire? Am I just be worried for no reason, I'm hoping it's just the lack of pressure and the heat building up.

When I touch it I can keep my hand on but it's pretty hot. I only had it running for like 7 minutes went to store, back in and home. The ride is like 3 minutes. Not sure if I'm putting the truck in danger, I'll be fine but this guy can't go out like that.

 

[Wes Harden]

7 min seems very quick for the cooling system to get up to full temperature.
The heater core will be at our near the thermostat temp when fully warmed up.
I am know wondering 2 things I'd the t stat opening? This would force all the flow through heater core.
Maybe exhaust heat into floor boards is responsible for some of the felt heat at floor vents.

 

[Irishmic]

It's the full system. As I put my hand inside to feel diffrent parts, behind the dash. It's as hot with the defrost area by the plenum. Right now I have a metal object holding the plenum open as I have not fixed the vaccine lines for it to open/close as it should. So it does get heat to go to the windshield. The best fix I could do to help with fog. I habe the new blower coming tomorrow.

I have watched the videos and they were helpful but I'm missing 4 tubes for the vacuum system to control changing where the air goes. Trying to figure out where I need to connect new tubes to. But for now still trying to figure it out

 

[85-K5Blazer]

@Irishmic I just went thorough putting in a new heater core and now I am finishing the AC..... I will draw out a schematic for you to attach new lines to the back of your vacuum selection switch as I was going to use new lines but decided to just use my original vacuum harness.

I will try to get this done tomorrow and sent it to you .... I am not going to be 100% on the location, but I will try to get you close. Mine is a 1985 K5 with a 6.2 L Diesel

 

[Wes Harden]

Not sure what you have propped open, all door should be in natural position for air to get to defrost ducts. Except temp which is cable controled.

 

[Irishmic]

Thank you 85k, that would be incredibly helpful.

 

[Irishmic]

Wes I have number 22 propped open. It will only stay on the closed position, that pushes all air to the floor. When opened its giving my windshield the much needed heat to get the fog away.

 

[85-K5Blazer]

As Wes mentioned earlier ...

You are correct 22 is the Defroster flap controlled by vacuum pod 21

19 & 27 control your Heater and AC controlled by vacuum pod 30

EDIT #1 .... Door 1 in dwg is the flapper door for your heater box to select Heat or AC

I still have not forgot you on the drawing I promised. I will do what I can after a meeting tonight ...

See the picture Wes Posted earlier ....

Your Vacuum rotary valve on the back of your HVAC will have 6 - 1/8" vacuum tips for the following: Knowing which Port is which is the clue ...

Vacuum from the engine - Port #1
Vacuum going to Defrost Pod 21 - Port # 5
Vacuum going to A/C / Heat Pod 30 (AC Side - Toward Engine) (This Pod should have vacuum ports on each side .. works as a push / pull unit) - Port #2
Vacuum going to A/C / Heat Pod 30 (Heat Side - Toward Interior)- Port 3
Vacuum going to OSA / REC Plenum ducts on Cowl and Body (this one splits with a "y" or "T" - Port 4
There will be one more Vacuum tip that is NOT used. EDIT #2 This port will have to be closed off with a vacuum plug as the factory harness had a blank plug line in them to keep the plugged off.
There will be two large posts that the vacuum harness lines up on ...

Knowing which tip applies to each POD is what I am going to send you ...