NOOOO Heat After Heater Core Replacement

86gtriceeater · Dec 2, 2011

I replaced my heater core because I was getting a fogged up windshield which would then freeze It got hot and I had heat before but the coolant on the windshield got real old. Now after replacing the heater I get nothing. By nothing I mean with the controls on "warm" the air doesn't even come out the vents. If put the temperature selector on cool I get air out of any vent I set it to. As i slide up the scale from cool to warm less and less air comes out of the vests (any of them I have it selected to) About half way up toward warm on the selector the air starts to slow then completely stops at about 3/4 the way up towards warm. Do I have the heater hoses to the core on backwards maybe? On the heater tube, the top one goes to the left (smaller tube) and the bottom tube on the intake heater tube goes to the right (larger tube) which is also the one that should have the coolant flow restrictor in it correct??? At no time does the air get even warm....Please help as its getting seriously cold here in Wisconsin and I wont be able to drive it anymore without heat. Thanks

BlackGT89 · Dec 4, 2011

I can't explain the strange action of your temperature selector controlling the air output, but can you tell if the hoses going into and out of the core appear to be hot with the engine at full temp ? If one hose is a good bit cooler it would imply an obstruction. Is it possible your restrictor in the hose got turned sideways (if you have one). I don't think you could reverse the hoses, different sizes I believe.

Noobz347 · Dec 4, 2011

The vac hose that controls the diaphragm between the heater core and blower motor in your air box is either broken or disconnected. Look at all the vac hoses up against your firewall and under the dash on the passenger side of your car. Follow them end to end. You'll find the culprit.

LarsD · Dec 4, 2011

Vacuum lines get my vote. I've had lots of problems with my HVAC that were caused by those old brittle plastic lines breaking on me.

Beasty306GT · Dec 4, 2011

prob a vac line....could also be restictor if it turned side ways..did u bleed all the air out after install

86gtriceeater · Dec 4, 2011

What diaphragm exactly? I've checked all tjw vacuum lines but nothing seems out of order with them. Also, my hoses have the same size ends so they will fit either way. Can I just remove the restrictor? I tried to bleed the air out but didn't make a difference

BlackGT89 · Dec 4, 2011

86gtriceeater said:
What diaphragm exactly? I've checked all tjw vacuum lines but nothing seems out of order with them. Also, my hoses have the same size ends so they will fit either way. Can I just remove the restrictor? I tried to bleed the air out but didn't make a difference

You really need that restrictor in the line. At some point Ford started putting them in the hose from the factory to restrict the flow into the heater core to prevent too much pressure under high rpm from damaging the core. Mine didn't have one so I made one myself from teflon.

Did you replace the heater core yourself, and if so, did you get all the vacuum lines back in the right place ? Just grasping at straws here.

BlackGT89 · Dec 4, 2011

I found this link with some great explainations and diagrams...
http://www.stangnet.com/mustang-forums/threads/ac-heater-control-problems-help.722738/

86gtriceeater · Dec 4, 2011

I did replace it myself but I literally didn't unplug any vacuum lines. I just took out all the necessary bolts from the dash to move it forward and get access to the core. I'm really stuck here...does anyone have pics of the heater tube hoses? I'm confident the hose with the restricter (the bigger one) goes to the bigger tube on the heater core, can anyone confirm this? Maybe my heater tube itself that runs from the core along the lower intake is clogged or something? Is there a way to check it without taking everything apart? Its a quick job but its really cold here. Thanks guys

86gtriceeater · Dec 10, 2011

I noticed there is very little coolant in my upper radiator hose even after fully warm. Any thoughts?

BlackGT89 · Dec 10, 2011

Sounds like you aren't getting enough water in the system and/or you have huge air bubble (no heat could be a clue for an air bubble). You might want to try a spill free funnel and burp the system while the car is up to temperature and running like in this video:

Keep an eye on the temp gauge and make sure you don't get burnt by the coolant. Also try and verify that your water pump is working properly and the thermostat is installed correctly.

Noobz347 · Dec 10, 2011

86gtriceeater said:
I did replace it myself but I literally didn't unplug any vacuum lines. I just took out all the necessary bolts from the dash to move it forward and get access to the core. I'm really stuck here...does anyone have pics of the heater tube hoses? I'm confident the hose with the restricter (the bigger one) goes to the bigger tube on the heater core, can anyone confirm this? Maybe my heater tube itself that runs from the core along the lower intake is clogged or something? Is there a way to check it without taking everything apart? Its a quick job but its really cold here. Thanks guys

Do you hear the vent box door changing positions when you move the HVAC control from full cold to full hot?

My guess is that you probably broke a vac tube somewhere while you were replacing your core. Like someone said above... they're old and brittle.

trbkrb · Dec 25, 2011

If your vacuum lines are bad, the air flow will default to the windshield. The vacuum only controls the location of the airflow. If you still get AC or vent flow out of your dash vents or the heater vents under the dash, then your vacuum is OK. Now the blend door that controls how hot or cold the air is, that is cable operated directly by the center AC control.

Reading what you wrote, that less air comes out as you change the blend door control to heat, makes me think the air passage in the heater section is blocked somehow. That is the only thing that makes sense to me if the air stops flowing out of any vents when you switch over to full heat. I assume the fan is still blowing full blast, right?

86gtriceeater · Dec 26, 2011

Yeah the fan stays on full blast, the air just slows coming through the vents as I move it toward warm. The cable that's attached to the temperature controls seems good and moves up and down with the temperature lever so I'm totally confused.

86gtriceeater · Jan 2, 2012

I still can't figure it out. Any fresh ideas?

Febreezeit50 · Jan 2, 2012

Well the cable is obviously working if you don't have any air flow. As its controlling the door that switches from cool/hot. The only thing i can think of being there is NO air in heat is like someone said above. Something is blocking air somewhere in the heater box.

NOOOO Heat After Heater Core Replacement

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