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Hi all,
Normally, I wouldn't think this'd be a problem as I've fixed my fair share of heaters before, but this one has me stumped.

This is on my '81 Bronco.

First off, the thermostat is only a few months old. Engine warms up just fine. Radiator is around a year old or so.

I replaced the heater core last weekend. Before reinstalling it, I filled it with coolant and did the same with the two hoses that run to it to make sure there were no big air bubbles in the system.

Coolant is topped off. I've checked it a couple times.



Next, the '81 setup is all cable operated. There aren't any vacuum lines that have to do with the heater controls. It's a super simple setup (which is why I'm stumped!) I only have two options to change. Either the blend door is open or closed (hot or cold), or the air blows out of the bottom vent or the defroster. (I don't have A/C).

While I had the heater box off, I cleaned out any and all leaves, and checked the functionality of the blend door. It moved freely and moved the full range of motion. It also fully sealed when closed.

I've checked that the slider in the cab moves the door in it's full range of motion. I can hear the blend door 'thumping' into place when it reaches the limits of it's range of motion. I've also gotten out and seen if I can move the blend door's lever in the engine bay any further and I can't.

The hoses going to and from the core are hot.



Yet, I've only got mildly warm air coming out of the heater! It took a good 10 minutes this morning with the engine fully warmed up just to melt the frost off the windshield, and after a 20 minute drive the cab wasn't even warm. The air blowing out of the vent just isn't all that hot. In my other Bronco (an '84), it's hot enough to sting your hand, so I know how it should feel.

Any ideas on this? I'm really not sure what more to do.
 

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Yet, I've only got mildly warm air coming out of the heater! It took a good 10 minutes this morning with the engine fully warmed up just to melt the frost off the windshield, and after a 20 minute drive the cab wasn't even warm. The air blowing out of the vent just isn't all that hot. In my other Bronco (an '84), it's hot enough to sting your hand, so I know how it should feel.

Any ideas on this? I'm really not sure what more to do.
Thats about how my 92 sounds. Its a big ass cargo area takes a while to warm it up.
You might want to check out your blower motor.
How is the output when you set it one cold?

Roman
 

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Discussion Starter #3
I would normally agree with you, but having two Broncos, I have another for comparison.
If my wife and I start them up at the same time and let them run for 10 minutes on a frosted over, 20° morning, her's (the '84) has all the windows, including the rear one (no rear defroster), fully melted and the cab's like a sauna if you don't turn the heater down.
Mine (the '81) will have a few spots on the windshield that have some melt on them.

Last I checked when I switched it to cold, it let the fridged outside air in.


I hadn't thought about the blower motor. It doesn't put out a lot of air, but I wouldn't necessarily say it's weak. I'll have to feel the output difference between the two.
 

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It the hoses are the same temp, I would look into the fact you probably have a blend issue and cold air is coming in instead of just hot air.
 

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Discussion Starter #5
It the hoses are the same temp, I would look into the fact you probably have a blend issue and cold air is coming in instead of just hot air.

I would think so, but I've checked the blend door. It moves all the way to the closed/open positions. And when I had the unit off, I double checked to be sure it fully sealed.
 

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you said the fan does not blow much?

Does it speed up from low to high? Does it blow as much air as the other bronco?
 

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Discussion Starter #7
It does change speeds, but not a lot. I'll check it against the other Bronco this evening when I get home.
 

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Sounds like the heater core is blocked or partiallly blocked and not letting enough not coolant through. Some heaters have a valve in the line from the water pump to stop the flow. If your's does check to make sure it's operating right.
 

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Post a pic of you set up if you can.

First make sure after running the engine the "top" radiator hose is hot indicating the T-sat is opeing and closing properly, not installed backwards.....it happens.......check the inline and return line heater hoses to make sure they're hooked up correctly, not reversed.....the inline hose comes out of the firewall hole on the right going to a tube/fixture threaded into the lower take, the return line comes out of the firewall hole on the left going to the water pump.

You don't mention "backflushing" the cooling system when you had it apart to replace the heater core....so add that to the list, it can't hurt.....it sounds like the blower motor isn't pushing enough air in over the HC, maybe it's a simple voltage/resistance issue so check the wiring.

My heat is stellar, hotter then shite even on low BUT I do have a new radiator, heater core and the engine was new back in 2008...

Let us know what you find out....


Good Luck ~ :thumbup
 

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you replaced the heater core but not the hoses, i think thats your problem, there must be something blocking the hoses
 

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Sounds like the heater core is blocked or partiallly blocked and not letting enough not coolant through. Some heaters have a valve in the line from the water pump to stop the flow. If your's does check to make sure it's operating right.
you replaced the heater core but not the hoses, i think thats your problem, there must be something blocking the hoses


His first post he said BOTH heater hoses are hot. That would lead me to believe his heater core is not plugged. If it was one would be cold.
 

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Discussion Starter #12


Here's a pic of the setup.
The hoses are hooked up correctly. Line to the water pump on the left, line from the T-Stat housing on the right. (The splice in the middle of one of the hoses is just a connector).
Either way though, what difference would that make? If I switched them, the fluid would only go through the heater core in the opposite direction.

I haven't backflushed the system, but the radiator was new last year, and all the coolant was replaced this spring.
I'll recheck the top hose, but I'm pretty certain that the t-stat is in the correct way. I replaced it this spring because I thought it was sticking shut, but only realized that the previous t-stat was in backwards. (What does a company expect when they put their brand name MotoRad on a thermostat and have the "Moto" on the end that faces the radiator, and the "Rad" on the end towards the motor?? :smilie_slap )
That being the case, I double and triple checked my Chiltons and Haynes to be sure it was in the correct direction when I replaced it.

What voltage should I have at the blower motor? 12v I'm assuming?
 

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Discussion Starter #13
Sounds like the heater core is blocked or partiallly blocked and not letting enough not coolant through. Some heaters have a valve in the line from the water pump to stop the flow. If your's does check to make sure it's operating right.
As said in my first post, the heater core is brand new as of last weekend.
Also, all of the aspects of my heating system are cable operated by the user. There are no check valves and nothing vacuum operated.
 

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His first post he said BOTH heater hoses are hot. That would lead me to believe his heater core is not plugged. If it was one would be cold.
not the core, im saying one of his hoses may be blocked somewhere, maybe at the end of the return line? so that it pushes warm air all the way through the core but doesnt quite make it back, so the coolant in his core gets cooled down by the blower motor and the hoses stay warm, but being that there is little to no flow through the core itself would cause a not so warm heater
 

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Discussion Starter #15
not the core, im saying one of his hoses may be blocked somewhere, maybe at the end of the return line? so that it pushes warm air all the way through the core but doesnt quite make it back, so the coolant in his core gets cooled down by the blower motor and the hoses stay warm, but being that there is little to no flow through the core itself would cause a not so warm heater
Hrmm... I hadn't thought of that. I had all the hoses off this summer when I replaced the engine, but the one I put in was used. I flushed it out as well as I could, but what's to say there wasn't some junk in it that plugged a hose.
 

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new heater core,
hoses hot,


I am thinking the core is getting plenty hot, he has a air flow problem. but thats just my 2 cents.
 

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not the core, im saying one of his hoses may be blocked somewhere, maybe at the end of the return line? so that it pushes warm air all the way through the core but doesnt quite make it back, so the coolant in his core gets cooled down by the blower motor and the hoses stay warm, but being that there is little to no flow through the core itself would cause a not so warm heater
That's really unlikley, unless he closed his eyes while doing all these repairs. He would of noticed all the titanic type rusty parts and such. I would check your blower motor.

Roman
 

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It does change speeds, but not a lot. I'll check it against the other Bronco this evening when I get home.
wire the motor directly off the battery and see if it blows at a higher speed.

there is a resistor that controls the speed which maybe defective.
 

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wire the motor directly off the battery and see if it blows at a higher speed.

there is a resistor that controls the speed which maybe defective.
I'll give that a try, shouldn't be too difficult.
If it does blow at a much higher speed, where is the resistor located? I'm assuming either wired directly to the dash switch or on the blower motor, or...
 

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you would have to look into your haynes manual. I am going to say it is going to be cooled by the blower fan, but I am not 100% sure.
 
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