The Heat is Always On (Ow, my toes!)

[Prime Lord]

So yesterday was the first good T-Top day in a long time. One problem, The incoming air through the vents passes over the heater core, gets stupidly hot, and then comes out of either the floor vent or the defrost depending on vacuum. This happens even when the ventilation system is turned off. And its speed related. It barely happens when going around town, but it gets uncomfortably hot when on the interstate. It burned my toes when I went to hit the brakes when cruising 70MPH.

What can I do about this? I don't have a vacuum reservoir or that other vacuum box that resides under the passenger side fender. The vacuum line for the vent system is simply T'd off of the line that supplies the EGR control valve.

 

[RsStanG1987]

do you have an off road h-pipe? stupid question i know

 

[Prime Lord]

Yes. I have an off-road H.

I noticed today that when there is vacuum the heat goes to the floor vents, when there is no vacuum it goes to the defrost. So I pulled the vacuum from the vent system and plugged the T. It now just goes to the defrost vents. But still...I don't understand why the system is passing air like this when the system is in the off position.

 

[aar0s]

the blower motor on my escort dont work but when i get to about 40 i can feel air blowing through the vents. Im guessing that its blow through but i have no idea why it would change from the floor to the defrost.

 

[BK_CAULEY]

your blend door is stuck open.

 

[RsStanG1987]

your blend door is stuck open.

Thats the prob mostlikely however i had a simmilar problem caused by my h pipe heating the floor up while at a stop. I diiddnt have the lower shift boot on and it would get crazy hot in the car. when i replaced it it stopped happening.

 

[jrichker]

Diagram courtesy of Tmoss & Stang&2birds

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 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 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 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 for94-95 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

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

 

[Prime Lord]

Yeah, I found that graphic last week and I've been staring at it for days now trying to wrap my head around it.

In the off position:
- Vacuum is applied to all valves
- The recirculator should block incoming air from entering the system

W/ that said relating to my problem
- I can see the recirulator flap moving up and down w/ vacuum. Unless there's another part of the flap I'm not seeing or it's not moving far enough that it closes off the incoming air
- I know that air is still getting into the system. When I see the recirculator flap in the up/open position from the passenger side there is a draft of outside air that you can feel on cold days.
- In a vacuum condition (decelerating) the floor valve is open. True.
- In a non-vacuum condition (accelerating) the floor valve is closed and the air is diverted to the defrost. True.
- I have never had air come out of the vents. Ever.
- I don't think I have a vacuum leak because if I move the selector at idle, the floor and defrost will operate correctly. Although it does take a while. Hrmm.

So my summation:
- The vacuum motor that opens and closes the vent/defrost flap is shot/disconnected
- something is wrong w/ my recirculator flap because it does not close off the ventilation system under vacuum
- I really kinda need the check valve and the vacuum reservoir.

Can you guys check my logic on this?

Also, I know the blend flap is kinda sticky. It takes a little bit of force to move it from cold to hot and it does not go all the way in either direction. Any tips on freeing that up?

 

[Prime Lord]

Okay, well I pulled out the vent controls and used a pair of vice grips to push the blend valve all the way to cold. So now its not heating, but I still have air getting past the recirculator. Any suggestions other than a check valve and a reservoir?