89 GT NO HEAT

[89stanggirl]

I have backflushed my heater core (which isn't leaking), flushed my radiator, changed coolant, new hi temp thermostat, new radiator cap, checked blend door (it is fine) blower motor works great, still NO HEAT!!! any suggestions would be greatly appreciated.

 

[BlownFiveLiter]

to :SNSign:

If the thermostat is good and the correct temperature, I would suspect air in the cooling system somewhere, if you're absolutely certain there's no leaks. Start the car with the front end on jackstands or ramps and the radiator cap removed. When the thermostat opens and the coolant begins to circulate when the engine reaches operating temperature, squeeze the upper hose (watch the fan blades and belt!) and see if you can burp any air out of the system. You want the front end raised, so that the radiator fill is the highest point in the system. Squeezing the hose repeatedly should help coax any air pockets out.

 

[89stanggirl]

Air

Thanks for the suggestion Matt, I failed to put that in my inital post, I already tried it per another suggestion. I am at a loss???????

 

[BlownFiveLiter]

Do you know if your thermostat is good, and the correct temperature? I believe the correct thermostat for a 5.0 is 190°, but I don't remember for certain.

 

[89stanggirl]

still nada

I tried both thermostats, a 180 and a higher temp 190, still nothing. I tried purging the system again last night (front end on jackstands-engine running-radiator cap off-squeezed upper radiator hose after thermostat opened) had a tiny bit of heat but no air and now NO heat.

 

[keithnra]

Are u 100% sure the heater core is flowing like it should be.R both hoses really hot to the touch, had a mercury sable do that one time and it was the heater core half clogged.

 

[89stanggirl]

heater core

yep, both heater core hoses are hot to the touch

 

[timeless2]

Thread relocated to Fox 5.0 Tech with redirect.

 

[f8tlfiveo]

If both the hoses are hot you are getting coolant through the heater core..if the blower motor works but still no heat you are having a problem with the door that controls the temp of the air..it is either operated with a cable or vacuum.. I think it's a cable though. I would check that because that is the last thing in the system that dictates heat or not.. If you pull the heat control switches out you will be able to see if it is vacuum or a cable.. I would put my money on cable because you can have the door halfway open for warm air. Rather than closed for cold or completely open for hot..

 

[89stanggirl]

blend door

I checked the cable that goes to the blend door, it operates fine. i cannot see the actual "door" i know the book says it is on top of the heater core????

 

[jrichker]

From the Ford manual....

The system uses a temperature blend method to provide controlled temperature to the vehicle interior. With this method all outside airflow from the blower passes through the heater case to the plenum assembly. Temperature is then regulated by heating a portion of the outside air and blending it with the remaining cooler outside air to the desired temperature. Temperature blending is varied by the temperature blend door which controls the amount of air that flows through or around the heater core where it is mixed and directed into the distribution plenum. The air is finally directed to the heater ducts, the defroster nozzles, or the instrument panel registers depending upon the function selected with the control knob.

The control assembly is located in the instrument panel at the right of the steering column. The control panel has three knobs marked SELECT, TEMP and FAN. The SELECT knob is for selecting the desired system function: OFF, FLOOR, PANEL (VENT), MIX or DEFROST. The center knob TEMP is for setting the desired temperature from cool to high heat. The FAN knob is a blower switch to control the volume of air movement. Each position of the SELECT knob and the FAN knob is detented for positive engagement. The FAN knob provides four manually selected blower speeds.

A cable assembly connects the temperature blend door with the function control knob in the control assembly. When the function control knob (SELECT) is in the OFF position, the temperature blend door is positioned to block passage of air to the distribution outlets.

As the function control knob is moved toward the PANEL (VENT) position, airflow gradually increases to full flow from the panel registers. As the function control knob is moved from the panel to the FLOOR position, flow gradually increases to full airflow from the floor heat distribution outlets and side window demisters.

When the function control knob is moved from FLOOR to the defrost (DEF) position, the amount of airflow from the floor heat distribution outlets will gradually reduce and the amount of airflow from the defroster outlets and demisters will increase.

With the function control knob in defrost (DEF), the air will be discharged from the defroster outlets onto the windshield and the demister registers onto the side windows.


Diagrams courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 86-95 5.0 Mustang wiring Mustang FAQ - Engine Information Everyone should bookmark this site.

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

Complete computer, actuator & sensor wiring diagram for 88-91 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 91-93 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 94-95 5.0 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/94-95_5.0_EEC_Wiring_Diagram.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

Vacuum Diagram 87-93 Mustangs
The diagram says 88 Mustang, but except for the vacuum line connected to the MAP/Baro sensor, it is the same for all 5.0 Mustangs from 87-93. The 89-93 Mustangs vent the MAP/Baro sensor to open air.
http://www.veryuseful.com/mustang/tech/engine/images/88Stang5.0Vacuum.gif

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pinout
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

 

[f8tlfiveo]

Yes it is.. Unfortunately you will have to pull the dashboard off like your replacing the heater core to get to the blower door.. I just did my heater core about 2 months ago.. It wasn't as bad as people say to get the dash out far enough to get to the heater box.. Just time consuming.. I did it in 3 hours start to finish but I knew where all of the bolts were that needed taken out.. There are write-ups online that give you step by step instructions. And if you do that just replace the heatercore while you have it apart..

 

[keithnra]

I thought about it and the write up that is just before me is execellent. the cable may be working but the door may not be opening, broke, i ve seen this before and no heat. good luck, the dash is not that bad ive done 3-4 of them but like they said go ahead and put a new heater core in there,.they are cheaop and might as well while u are in there.

 

[ID89GT]

Drop the glovebox and you will see where the blend air cable goes just behind the controls. Operate it and see if the door is actually moving. This was my problem before, my cable was kinked so it wasn't opening all the way and warm air never came in. I put a different cable on it and now it works perfectly.

 

[89stanggirl]

I replaced the coolant temp. sensor, to no avale. This is going to sound crazy but, do I have a heater control valve? Where would it be?

 

[ID89GT]

No there is no heater control valve.

 

[89stanggirl]

alright, i got the dash completely out, all "doors" in good shape, working properly. guess i will replace the heater core and hope for the best

 

[ID89GT]

Try moving the blend air door by hand and see if you can notice a difference in temperature change.

 

[VanD]

lots of good info, subscribing for when/if i feel like messing with mine