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I have a 94 bronco, that i just picked up and ran great until winter hit no heat, unhappy wife, and then i started smelling antifreeze in the cab, heater core of course. so i replaced the core no problem but still no heat, so i checked the hose and they are now getting hot, so i replaced the thermostat just to be sure...nothing, so i went ahead and replaced the rad cap to ensure a good seal. still no heat:banghead so i started checking vacuum lines, i have good vacuum at all the points i have found, the selector switch changes the air flow where it should go (vents/floor/defrost/mix), but only blows warm (not hot) air when on max air. when i turn on the vent selector it blows hot for a couple of seconds and then you can hear the door shut and back to cold air...the heater core gets hot i have vacuum...wtf do you do next.
 

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I have a similar problem in my 86 when I move the selector to floor or defrost it won't blow air much, but my heat is killer. There are little vacuum canisters inside the dash PITA to get at so you have to pull it apart for R & R and mine has three. Under the hood above the heater hoses there is one of those canisters for fresh air which may affect the trap door. I replaced my radiator, thermostat, all hoses and heater core because it was leaking and smelled.
Did you put a good seal around the core in the box?

Just as an added trick, you can solder a piece of wire to the core and ground it under the kick panel to the sheetmetal which will stop the galvonic processs (not electrolysis) so it won't rust into the system.

You may want to go inside where the blower motor is and see if there is any debris like leaves etc.

Good Luck ~ :thumbup
 

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i get plenty of air flow, it just won't heat up. i found 3 of the canisters but all seem to be working, a friend at the mechanics shop told be that i may have to much "flow" whatever that means and that is why the heater door is not staying open, and why the hot air comes out cold. i will check that canister again tonight, but to get to the third one i have to take my dash apart, unless someone knows a trick to get to it. i found some grass in the box when i opened it but it's clean with a good seal now.
how much more can there be to a heater...heat up water, run through core, blow air across, have warm feet. :doh0715:
thanks again
 

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It seems that we both have the same problem so I'm wondering if someone can help me on this too. Save posting a new topic.

Done a lot of searches on this, and have done a lot of work on my heater too, but nothing I seem to do gets the heater hot enough to actually make it comfortable in the cab during the winter. It's enough to keep the chill out, but you still need a jacket for long trips.

I've flushed the cooling system, replaced the radiator with a new one, replaced the heater core with a new one, BOTH heater hoses going into and out of the heater core are HOT HOT, new thermostat, the cable slider that opens and closes the heater door moves the arm the full range, and the fan blows nice and strong. Just doesn't get very hot.

I have an '81 and from what I've heard, I didn't think they started adding vacuum heater controls until a few years later. Does an '81 have any of the heater components operated by vacuum? I know my slider (cold<<<<>>>>hot) is cable driven.

Thanks.
 

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Discussion Starter #8
my heat cold switch is cable driven too...
how do you get to the heater door...i haven't dug into far in yet, but mine seems to be sealed up pretty good. i know i sound like a newbie but haven't worked with heat or ac yet...
 

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I have a '92 w/351 and I have the same problem. I just pulled out the heater core again yesterday, just to make sure the vent door is opening and shutting properly, it is. I checked the vaccum hoses and they all seem to be in good shape, pulled the blower motor assembly and everything seems to be fine there as well. It's not rocket science, or is it. I've had this problem now for the 2nd year in a row. I was having great heat and air flow until I changed the bad heater core 2 years ago. Could it be a bad core? If you or anyone else finds the answer keep this post here, thanks, cold as hell guy.
 

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I have a '92 w/351 and I have the same problem. I just pulled out the heater core again yesterday, just to make sure the vent door is opening and shutting properly, it is. I checked the vaccum hoses and they all seem to be in good shape, pulled the blower motor assembly and everything seems to be fine there as well. It's not rocket science, or is it. I've had this problem now for the 2nd year in a row. I was having great heat and air flow until I changed the bad heater core 2 years ago. Could it be a bad core? If you or anyone else finds the answer keep this post here, thanks, cold as hell guy.
I once had a Mustang that would not produce hot air for defrost or cabin heat. I found the heater core box was full of straw/string/leaves from a mouse nest building project. I had wondered about musty odor in the car. Cleaned out the mess and had heat to spare.

The best way to check operating status for the vacuum cannister is to connect a mighty vac device to them. These cannisters not only have to operate once vacuum is applied but also hold vacuum during engine acceleration when engine vacuum drops.
 

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Discussion Starter #11
ok worked on the truck last night...and by work i mean chase a bunch of lines under the dash, drink a lot and cuss...though it made me feel better to do the later i don't think it helped the problem and this morning was cold as hell driving to work like a dang eskimo. I think dan is right about losing vacuum when driving...now since i have no suck-a-pump to test the vacuum i guess i go back under the dash. If anyone has any other suggestions please help
thanks everyone
 

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ok worked on the truck last night...and by work i mean chase a bunch of lines under the dash, drink a lot and cuss...though it made me feel better to do the later i don't think it helped the problem and this morning was cold as hell driving to work like a dang eskimo. I think dan is right about losing vacuum when driving...now since i have no suck-a-pump to test the vacuum i guess i go back under the dash. If anyone has any other suggestions please help
thanks everyone

Dude, you're in TX, isn't it hot there? :whiteflag Sorry.

You mentioned earlier in the thread that your hoses were not getting hot. No heat in the hoses, and no heat to the heater core, no heat to the cabin. Does the upper radiator hose ever get hot? Do you have a plug in the hose to the core? (ie - do you have flow?) Corrosion in the water pump that it has either blocked or nearly blocked the output to the heater? You are all right, this is not rocket science - at least the making hot water go to the core part. The vacuum stuff is ALL freakin' rocket science. :)
 

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bhansard13:
Are you sure the thermostat is opening up?
If you run it around for 10-15 minutes and shut it off the top radiator hose should be hot indicating the thermostat is working.

When was the last time you backed flushed the motor/system ?
(clean water only)
Are yo sure the heater hoses are hooked up correctly?
WHAT IS THE TEMP # THERMOSTAT YOU INSTALLED?
Is the blower motor really pushing air properly?

If yes to all, it has to be blockage or vacuum leak somewhere, no?

Good Luck ~ :thumbup
 

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I would also check the vacuum line (white) that can be seen on the passenger side when hood is open. It goes directly to the HVAC box at the firewall. This vacuum line is a common failure (it dry rots). Cut out any bad section of the original plastic line and replace it with the proper sized rubber hosing...

Another problematic vacuum line area would be ALL of the plastic vacuum lines that are concealed inside of the black conduit wrap that can be seen routed along and around the upper/lower intake on the engine. DON'T ASSUME that your vacuum lines are "ok" just because 1) they cannot be seen and 2) you don't hear any air leaks... On my prior 94, I had removed the entire vacuum line assembly from the engine (very simple to do), removed all of the outer black conduit and found that 2 of the inner plastic lines were actually cracked - causing an unseen (and unheard) vacuum leak... To repair those bad areas, I just made clean cuts where the cracks were found and bridged the break with the appropriate sized small pieces of rubber vacuum line... Once all of the cracks were fixed and the vacuum lines were reinstalled, you would not believe how many other issues were fixed (including inoperative heating, inoperative vents, inoperative HVAC solenoids, drivability, etc etc etc)...

If it were me w/ your vehicle, I would take the time out to do the same as I did on my prior 94... Those original vacuum lines that are concealed in the conduit do become brittle over the years due to heat, cold, expansion & contraction and will eventually crack or break.

Good luck!
 

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Discussion Starter #15
Thanks everyone, i have a T195 thermostat in it now but it seems to take the truck longer to heat up...top hose gets hot heater core hoses get hot...(side note the fan spins really well...kids asking questions and almost lost a finger...:smilie_slap)
i am going to take cobra man's advice if it will improve more than just heat i'm in for chasing some hoses...never want to say that again...yuk. let you know how it turns out...i
 
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