For 79-93 Mustangs

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.

First, The HARD WAY...

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.

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.

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.


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 core half way out of the hole. It slides out very easily.

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.

Also, visit the FAQ Page for more info on heater core replacements