heater mystery

[junkyarddog]

Hi guys, I have a heater problem. I know this has been discused at length however, I haven't solved my problem and have questions. I got a new heater core but the heat still will not blow hot. So, I took someone's advice and removed the blower motor and cleaned out all the crud inside the box that the motor bolts to in the engine compartment. WHen I took the motor out, I noticed a flapper door inside the box where the motor bolts. It appears to be actuated by a some kind of solonoid switch with a little plastic vaccuum line attached to it. What is this door for? Is it supposed to open when the heat is on? That solonoid is on the outside of the box right next to the fire wall. Right now, it doesn't open the door when the heat is turned on. The door looks like it opens into the cab into the compartment where the heater core is located. I guess this is why I am asking. It's on a 90 full size with 5.8 liter motor. I wish I had pics but I don't. Thanks for any advice. By the way, both of the coolant lines that go to the back of the heater core become hot when I run the heat so I know it isn't any kind of obstruction in the lines or core. Thanks again

 

[noahsdad86]

I too am interested in this answer as my heater works fine but only blows through the defrost vents. i would love to put some heat or my toesies or on my arms when it is cold

 

[Big_Brown_Bronco]

I am new here as well, and this is my first post, but from what I have read and what *I think* is that that is the vacuum solenoid(?) that actuates the internal air diverter. It shouldn't have anything to do with not having heat in the cab. And for Noahsdad86, If you are only blowing air through your vent (like mine does), you more than likely have a vacuum leak that needs fixed. I haven't had time to go through the lines in my engine bay or dash yet.

 

[Broncobill78]

That's the blend door, it opens & closes in response to the temp control slider on the dash. If it's not actuating then that's why you have no heat it's supposed to mix hot & cold air to provide the temp that you've set the temperature slider for. Fix it & you'll have your heat back.. On a 17yr old truck odds are pretty good you've got a split vacuum line somewhere or a cracked/broken vacuum ******. I know some of the cars use an electric blend-door motor but all my Broncos have always had vacuum actuated blend doors but to be honest I haven't taken the dash apart in one of the newer Broncos yet to see but you should be able to tell by looking at the back of the temp control & seeing if it's got vacuum lines running to it. Also, you can usually *hear* it hissing as it actuates the door when you slide the temp control up or down, if it used to hiss when you changed temp and it's not doing so any longer than that's a pretty good indication of what your problem is.

 

[junkyarddog]

Hi Broncobill, thanks for the help. I didn't have to take the dash apart to get to this door. I just had to remove the blower motor in the engine compartment from the box protruding from the firewall. Is this the door you speak of? here's what I did to make the heat work (sort of, it's not really hot, it's just enough to defrost the windshield), I made that door stay open all the time. I am getting better heat but it's not as hot as I would like it. Understand that this is just a temporary fix. I don't like rigging anything but I had to because of the insane snow and weather we are getting in Denver right now. Thanks for the help.

 

[Roadkill]

I'm not sure exactly wich year it changed, but my '96 Bronco has a cable between the temperature **** and the blend door, all the other functions are still vacum operated though. I'm just guessing but I would bet it changed in with the '92 models. I have read about isues with the conection between that cable and the blend door breaking.

 

[Broncobill78]

Well, to be honest, the only ones I've ever torn down to componant level were the 78/79's. I've done several of them and there's no real mystery there. I haven't had to disassemble an 80-96 yet. I don't even HAVE heater hoses running to the heater core for my 88' and I'm not in any hurry to replace them. It was 82 today, but having grown up in New England I appreciate your position. It gets freaking cold up North (that's WHY I live in South Florida. I HATE the f*cking cold).

If you're stuck for something to do then I'd just jam the blend door open to get the max heat available. If it doesn't seem as warm as it should check for leaks. I've had more than a few trucks with core/door leaks that bled heat off into the engine compartment instead of the cab.

As another idea, in the past I've run a manual choke cable to the blend door control arm and used THAT to manually set the door position when I ran out of patience dicking around with the vacuum lines. It's not an ideal solution but it DOES work and it keeps you warm when the winter winds are blowing. I used a propane torch to heat the end of the choke cable cherry red & then wrapped it around the end of an awl to give me the circular end I needed to drop it over the door control arm. Your mileage may vary.

 

[Scooter]

Hello Gents!! Wanted to post a THANKS to you guys for all of the info I got tonight!! > I have an 89 Bronco XLT 4X4 that I've put quite a bit of money into fixing up and didn't have heat either (no snow here to speak of, but ID is chilly this time of year!! was 20 degrees on my way to work today). Never got the blast of antifreeze through the vents (like I did in my Zcar when the heater core went in it) so opted to "try" to be intelligent (for a girl anyway) and start hunting for another reason. I'm very glad I did!! Will dive into it this weekend and probably come back and thank you again as well as post some pix of her...for an 89 she's aweful perty...inside and out for being all original body and interrior!

 

[Broncobill78]

Hello Gents!! Wanted to post a THANKS to you guys for all of the info I got tonight!! > I have an 89 Bronco XLT 4X4 that I've put quite a bit of money into fixing up and didn't have heat either (no snow here to speak of, but ID is chilly this time of year!! was 20 degrees on my way to work today). Never got the blast of antifreeze through the vents (like I did in my Zcar when the heater core went in it) so opted to "try" to be intelligent (for a girl anyway) and start hunting for another reason. I'm very glad I did!! Will dive into it this weekend and probably come back and thank you again as well as post some pix of her...for an 89 she's aweful perty...inside and out for being all original body and interrior!

Well let us know how you make out. That maple-syrup scent thru then heater vent is always a dead give-away but you can have all sorts of other problems. I spent close to 40yrs north of the Mason-Dixon & I'll never know what posessed me to do it. Finally after a few years working out in the Gulf I decided southern Fla was the way to go. I don't even HAVE heater hoses running from my water pump to the core right now, $hit it was 82 today (and yesterday for that matter). But everyone here is willing to help, so just shout out, that's what everyone else does.

 

[Seabronc]

I am new here as well, and this is my first post, but from what I have read and what *I think* is that that is the vacuum solenoid(?) that actuates the internal air diverter. It shouldn't have anything to do with not having heat in the cab. And for Noahsdad86, If you are only blowing air through your vent (like mine does), you more than likely have a vacuum leak that needs fixed. I haven't had time to go through the lines in my engine bay or dash yet.

The system is very simple and yes only going to the vents is the default if the vacuum system fails. Usually because of a bad vacuum reservoir or a break in the line from the check valve to either the reservoir or the heat controls. Some have a round plastic globe and a separate check valve, some have a coffee can with a built in check valve (the can rots out), some are a fairly large unit on the passenger fender with other stuff around it.

Good luck,

>-

 

[junkyarddog]

Seabronc, thanks for the diagram. That's kinda what I was looking for in my Heater Mystery post. I needed to find where the blend door is located. I thought it was inside the compartment where the blower motor bolts to but that apears to be the door for outside recirculated air. That diagram is a great help. Thanks to everyone else who helped out with this too

 

[junkyarddog]

I just went out and took the glove compartment door off and felt around the box with the heater running. There are leaks in the box. The air coming from the leaks in the box is hotter than Georgia asphault. I suspect that this is a large part of my problem. The heat from the vents is warm but not hot. The other thing I discovered is from my local shop. The guy says that when whoever put the new heater core in, they may have neglected to put the foam around the core. He says it's a seperate kit that doesn't always come with a new core.

 

[Broncobill78]

I just went out and took the glove compartment door off and felt around the box with the heater running. There are leaks in the box. The air coming from the leaks in the box is hotter than Georgia asphault. I suspect that this is a large part of my problem. The heat from the vents is warm but not hot. The other thing I discovered is from my local shop. The guy says that when whoever put the new heater core in, they may have neglected to put the foam around the core. He says it's a seperate kit that doesn't always come with a new core.

HA ! just what I was going to post. Those cores have a 1/2" foam "gasket" around them that tends to crumble with time. There's a VERY good chance you're just losing the warm air before it ever gets to you. I've replace more than a few of them with Home Depot foam, there are all sorts of fixes from the Ford kits to those cans of expanding foam. Personally I'd stay away from the canned stuff, it's a bitch to clean up. Either way you need to get a handle on the leaks first.