No Heat

mricci

Member
Aug 17, 2003
301
0
17
Massachusetts
With the snow the other day the driveway had to be plowed so i started up and moved the car for the first time in a little while. Its a 1990 lx with gt-40 intake as the only mod. The car started right up and warmed up to temp by the stock gauge. Everything was fine until i got in it to move it and the heater was still blowing ice cold. The first thought i had was a heater core. I was just wondering if it could be anything else before i go through the hassle of replacing the heater core.
 
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Probably a vacuum leak that disables the heater controls.

Diagram courtesy of Tmoss & Stang&2birds
Mustang_AC_heat_vacuum_controls.gif


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ 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

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
 

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Jrichker, isn't the blend door cable operated? It looks like the OP has a 95 GT, in which case, it is.

Check the operation of your blend door, to see if it's in fact opening and closing. Also check the coolant level, to ensure that you don't have a heater core full of air, and that you're getting proper circulation.
 
How long are you waiting for heat?

On warm up the gauge will go up over
normal then come back to normal. You
still will not have heat for at least 5 minutes more as
the water circulates.
 
I vote for blender door, try this.......

Warm car up good and touch both heater core hoses going into the firewall....if only the one is hot it's prob clogged or whatnot, if both are Hot, then it's most likely your blender.
 
Blend door is mechanical. Even with a vacuum failure it should still default to blowing warm air out of defrost.

Check your coolant level. Make sure the rad is full.

Then check if both heater hoses at the firewall are about the same temp
 
Blend door is mechanical. Even with a vacuum failure it should still default to blowing warm air out of defrost.

Check your coolant level. Make sure the rad is full.

Then check if both heater hoses at the firewall are about the same temp

Only one that thought this? Most of the time, it's due to low coolant. Even a little bit will cause this problem. Since the air is blowing, heater blower is working. Check this first, very easy fix.