Heater Core
Replacement

For 79-93 Mustangs
Hook this "test tube" up to the two tubes on the heater core and
submerge in water.  Add air until the bike tube balloons out, and
watch for bubbles.  No bubbles = no leaks.
Heater core exposed without removing heater box OR
disconnecting the A/C hoses
The "High Tech" core
testing equipment...
The hole where the core was removed...
Cut the heater box open with a cut-off wheel and die grinder. Then, slide the
heater core straight out.  Push the new core back in place, being careful that the
tubes go through the holes in the firewall insulation.

The beauty of this method is that you do not have to evacuate the A/C freon.  The
A/C system is not touched.

When you get the new core in place, simply silicone seal the old pieces of the
heater box back in place.  Finish it off with some duct tape.
The core half way out of the hole.  It slides out
very easily.
NOW, For the EASY WAY TO DO IT...
Related TIP:   The vacuum fittings tend to get loose and
leak at the switch connections.  The FIX is to cut short
lengths of rubber vacuum hose and stick them into the
cavities in the back of the vacuum line plug.  That makes
the tubes fit tightly.  If your A/C only blows out the lower
heater outlets, this is likely the cause.  This fix costs less
than $1.00
Under the hood, the heater hoses and the A/C dryer connections
must be removed.
IMPORTANT HINT:  Be sure to unbolt the dryer from it's
retainer bracket before attempting to unfasten the A/C
connections.  If you don't, it may make the soft aluminum
threads strip off.
Another TIP...  Solder a piece of copper tubing between the tubes
of the new core to stabilize the tubes so they can't vibrate loose
from the tanks of the heater core.
This shows HEATER CORE removed from 1988 Mustang.  Note the entire dashboard was removed and the entire heater and A/C box under
the dash had to be removed to access the heater core, which mounts right under the cowl.  A/C system must be evacuated to remove the
heater box from the car.
View of firewall from inside car
after heater box is removed
First, The HARD WAY...
Shows the heater box in place
Also, visit the FAQ Page for more in fo on heater core replacements
LOTS OF PICTURES, it may take a while to load...
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