Hi,

This fall I replaced the heater core so that I would be ready for this winter (old one was leaking), but something isn't quite right. Heater blower runs fine, and all dashpots operate, but I'm not getting air movement like I'm supposed to.

When I change from vents to floor to defrost, the dashpots operate, but the hot air doesn't seem to change "direction", and the volume is very low. It's hot, but not enough movement, and not directed to where it's supposed to go.

In what order do I need to diagnose this issue? What do I need to look for?

Thanks!

 

I never had this problem, but there are some posts on here about a blend door hinge that breaks in the duct.

 

Does it blow good when the heat is off? Could be a air leak too. I had one of the door's foam seal fall apart and cause poor air flow.

I have my 84 heat/AC box apart and can get photos for you tommaro.

 

I'll check it with heat off.

PHOTO'S PLEASE!! That would be great.

How do you go about getting foam seals back in place. I know mine are bad, because I see the stuff blowing out of the floor vent from time to time....

 

I have a problem with mine (1986) changing from A/C to defrost, it will only blow out the vents so I removed the access panel for the heater core and can see inside the box and the white door that allows it to block off the vents gets hung up on the heater box (I think it is worn out) the actuator works fine so a little nudge from my hand and it will release and close to the defrost mode, just don't switch back until the weather gets warmer. This is what mine is doing could be your problem as well.

AS for the black foam seals you will need to take the heater out and take it apart to replace the seals.

 

Here's some photos of a 84 AC/heat box from my truck. The foam seals are on the doors and are falling apart on mine. The air recir door is rusting apart on my truck but that should not cause poor heater operation for yours. Most likely when you put heat on there is more resistance of air going through the heater core, that can cause air leaks in the AC evap area.

Getting that thing out of your truck is not easy as the bolts usually strip the plastic housing(blind bolts) and some bolts are hidden!







Temp blend door


Temp blend door lever



Make sure this area is sealed really good, see the white RTV all over the place.....

 

I was getting low flow from the defrost for the last couple years. I finally took the dash pad off (5 minute job) and found the drivers side clogged with a mouse nest. I can see again!!

 

Better check your wireing and everything else, Those little $#!t's probly ate up other things.

 

If there's some distortion of the ductwork or the door itself you can use a heat gun to make it pliable enough to tweak it back.
Handle with gloves and use a wet rag to cool it, it will stay, at least for a while.
Try some of the adhesive foam weatherstripping tapes available at the hardware or home center if your seals are deteriorating. Scrape and vacuum the crumbling junk out and wipe with alcohol before trying to stick the new weatherstrip on.
Again, at least a temporary fix to keep you warm or your windshield clear.

 

I realized that if the dash comes off I will be able to access the door that I am having trouble with as this just blocks off the vents from operating.

 

Quote:

Originally Posted by ArdWrknTrk

Try some of the adhesive foam weatherstripping tapes available at the hardware or home center if your seals are deteriorating. Scrape and vacuum the crumbling junk out and wipe with alcohol before trying to stick the new weatherstrip on.

I don't remember exactly what I did for the box <-> firewall connection, I
think made a bead of some sort of silicone rubber on the firewall where the
box mounts, my original rubber seal there wasn't so bad.

The foam rubber on the inside, though, was shot, it turned to dust just
touching it. I scraped all that off, washed off the old glue with acetone or
some such, then glued on 1/4" foam rubber that was originally old packing
material.

No AC on my truck FWIW.

 

So I guess what I need to do here is to pull the cowl, the dash pad, and the blower for general cleaning and inspection. I'll also pull the heater core cover just to check things out. Might as well pull the resister just to make sure I don't have a pile of kindling there, waiting to start a fire?

I'll save the internal seals for later this spring. I'm just trying to get enough air flow (in the right places) to get me through the winter. Tearing the heater out is a project best left for warmer weather, as I don't have a covered garage to work in. I am the literal "Back Yard Mechanic"



Thanks guys!

 

If I were you I would find the problem and correct just that.

Unbolt the fan from the plenum, vacuum out what you can from there.
The cage is likely full of "stuff" and not moving any air.
Remove the heater core cover, behind the glove box if you have A/C.
Check the function of the doors and flaps that you can reach from there.
Blow or vacuum heater core if clogged with debris.

You can reach a lot of it without having to remove the entire dash.

 

So I'm kinda bummed right now.

I removed the cowl screws, but could only get the drivers side to lift up a little bit, because the antenna was holding me up from completely removing the cowl to clean up under there. I was only able to reach the junk on the drivers side. Got most of it out, but I'm not sure if I did any good. Where exactly do I need to clear under there for good air flow? Is there a trick for completely removing the cowl?

Then I pulled the blower motor, and stuck my hand in where the a/c evaporator is, and pulled out LOADS of leaves and twigs. It was packed! Cleared and vacuumed all I could.

Looking in through where the blower motor was removed, there is a door that is operated my a vacuum thingy just above the blower. Door one way, and I can see down into the kick-panel. Door the other way, and I can see directly into the cab. Vacuum thingy seemed to be working ok. I guess when the door is open to the cab, that's recirculating cold air when the a/c is on? Seal looked ok on that door.

I cleaned out leaves and candy wrappers out of the kick-panel area.

Still low air volume. I'm thinking the a/c evaporator has clogged fins, or there is still more crap I can't reach. How hard is it to remove the whole blower/evaporator unit from the firewall? I don't have to worry about discharging the a/c, as it's never worked anyway. I never use a/c....can I swap out a non-a/c housing for this one? (just wondering...maybe for later)

I was thinking that if I remove the blower/evaporator unit I can better clean out all the crud, and then I can be sure that any other issues are behind the dash, right?

 

Recirculate not only works w/ A/C.
If it's open the freezing cold air only has one pass through the heater core.

I don't have A/C so I'm afraid I can't answer your question as to whether the housings will swap, but I'd imagine you could just remove the evaporator coil and seal the holes left by the lines.