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For awhile now my heater has been acting up. It will blow cold air even if the car is hot. You have to turn the HVAC system on and off a TON of times before it will finally blow hot air.

Normally once it starts its good to go and will stay on.

Any ideas where I should start on this? Its starting to get quite cold here in MS and I want my heat!
 

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when it does come on, does the air come out of the primary vents or the vents at the glass? Can you switch between the two?
 

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zat, Mine was doing the same. I than Blew the to Radator hose and when I bled the system after the install of the new one, My heater worked again. Maybe Try Bleeding the cooling system
 

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burp your coolant system.


1.Remove Radiator cap
2. fill to bottom of the neck
3. leave cap off and run until thermostat opens
4. watch the level inside the radiator and when it drops fill it

That is the just of it
 

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2013 5.0
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burp your coolant system.


1.Remove Radiator cap
2. fill to bottom of the neck
3. leave cap off and run until thermostat opens
4. watch the level inside the radiator and when it drops fill it

That is the just of it
Hmmm, I let my coolant run completely out... not smart, but most likely why my heat stopped working... I guess I'll do this...
 

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No you shouldn't lose any coolant. What happens is that the heater core is the highest part in the system. air will go to the highest part.

take that radiator cap off and then turn the car on. use a flashlight and once you see the coolent to start flow. the level should drop if there is air in the system. make sense
 

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2013 5.0
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No you shouldn't lose any coolant. What happens is that the heater core is the highest part in the system. air will go to the highest part.

take that radiator cap off and then turn the car on. use a flashlight and once you see the coolent to start flow. the level should drop if there is air in the system. make sense
gotta fill it slowly right? since its such a small space? I only ask because I used to fill up from the coolat reservoir and someone told me that was wrong.
 

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Discussion Starter #10
could be your thermostat
It's been replaced since this started.

when it does come on, does the air come out of the primary vents or the vents at the glass? Can you switch between the two?
It depends on which ever it's set to? I can switch where the air comes out of, yes.

zat, Mine was doing the same. I than Blew the to Radator hose and when I bled the system after the install of the new one, My heater worked again. Maybe Try Bleeding the cooling system
This has also been done since this issue started.
 

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gotta fill it slowly right? since its such a small space? I only ask because I used to fill up from the coolat reservoir and someone told me that was wrong.
Most coolant systems have the reservoir NOT pressurized. In the Mustang, at least in the NE V8, the reservoir is pressurized and is the ONLY place you can fill. If you're vehicle has a radiator cap and a reservoir cap, you should fill from the radiator cap.
 

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I'm having similar issues, I changed the thermostat and hoses and put in a new radiator... starting to think it's the water pump. Over time the blades can rot away so it might not be pushing the coolant like it should. Haven't gotten around to checking mine yet, just a thought
 

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Well if the switches and fans are working fine then wouldn't it be a bad heater core? Sounds like there's no coolant running through the heater core to heat your passenger compartment.
 

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Well if the switches and fans are working fine then wouldn't it be a bad heater core? Sounds like there's no coolant running through the heater core to heat your passenger compartment.
I'm pretty sure there is some type of vacuum system behind the dash that actives the vents and switch from A/C to cooling modes. If that isn't working properly that could be the problem.

Maybe something similar to this thread?

http://www.moddedmustangs.com/forums/99-04/162447-c-heater-vents-not-working.html
 

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So here's an update on mine: I've noticed that when the temperature knob is turned all the way to the right (red - heat) and I try to turn it to the left (blue - cool) the knob feels pretty stiff like I'm pushing again something. However, when I turn it to the right, it feels rather soft and there is almost none, if any, resistance, it's just softly turns. Not sure if it's related to the vacuum system, but maybe.. I really don't want to pull the dash.... :-(
 

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Discussion Starter #20
So here's an update on mine: I've noticed that when the temperature knob is turned all the way to the right (red - heat) and I try to turn it to the left (blue - cool) the knob feels pretty stiff like I'm pushing again something. However, when I turn it to the right, it feels rather soft and there is almost none, if any, resistance, it's just softly turns. Not sure if it's related to the vacuum system, but maybe.. I really don't want to pull the dash.... :-(
Mine is the same way... can anyone without problems comment if theirs is like this? Would rule it out as a problem.
 
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