Heater Core Replacement

The following How To explains how to replace the heater core in AC equipped 1985 Mustangs and Non-AC equipped 1985 Mustangs. Relax....The AC heater core change is not as bad as every one makes it out to be. It is time consuming and tedious but with a little patience you will have it done in no time at all.

Tools:

• Assorted Hand Tools (I.E. Screw drivers,wrenches and sockets.

• 2 Piece of wood with 2"x4"x1' dimensions

• JB Weld (Optional) If you are not using the Ford replacement heater core I suggest you apply JB Weld to the tubes ends where they meet the heater core to stiffen up this area. Be careful not to add to much as this may restrict the heater core from fitting into the heater box correctly.

AC Equipped Mustangs:

• When taking out the heater core on an AC equipped car, you do not have to drain the AC system. But you must be very careful not to damage the AC lines or any of the AC accessories. You don't want to create more problems for yourself.

• Drain the antifreeze from the cars cooling system VIA the drain cock on the radiator. Note: f you do not have the drain cock release the fluid through the lower radiator hose.

• Disconnect the heater core water lines from the heater core tubes protruding from the passenger side of the firewall in the engine bay.

• Loosen the AC dryer from the firewall by loosening the nut a bolt that is compressing the holding ring. Do not remove the bracket from the firewall.

• Remove the 2 nuts from the studs that are protruding out through the firewall. In the picture below you can see three bolts that hold the AC/Heater box to the firewall. The lower screw bolt is only accessible from the inside of the car.

• Inside the car, remove Dash pad (11 screws). Note there are four along the windshield area in the defroster vents. Three above the gauge cluster face plate. One behind the gauge cluster face plate, above the AC/Heater controls, and the remaining three screws along the passenger side panel.

• Remove the glove box from the dash. Three screw from bottom of dash just below glove compartment.

• Remove the lower air ducts behind the radio, you may want to remove radio(2 screws) if you feel it will give you more working room.

• Remove the two bolts below the radio that are securing the dash.

• Remove the 4 interior heater plenum screws.

• Remove the lower passenger kick panel and right side lower dash bolt (one). This bolt is locate at the bottom of the dash where the kick panels meets it.

• Pull out gently on the dash and use a piece of wood to hold the dash out. The wood should be placed between the dash and the kick panel pillar. You will only be able to pull out the dash out a little bit so don't get to wild or you may crack certain plastic portions of the dash.

• Reaching through he glove box pull out on the AC/Heater box being careful not to damage the AC lines going into the engine compartment.

• Locate the heater core cover panel located on the top of the AC/Heater box. Remove all the cover bolts. The back two will be difficult and take some time. Be patient! Others have used a dremel to cut around these screws but I recommend you take you time and remove them correctly.

• Once the cover panel is removed remove the heater core from the AC/Heater box.

• Clean up all factory sealing goo off the cover area and AC/Heater box.

• Practice how you will get the new unit into the AC/Heater box using the old damaged unit. This way you know the best way to get the core in there without damaging it.

• Once you feel comfortable with your process of installing the new core, do so taking extra care not to damage the new heater core.

• Remove the glove box from the dash. Three screw from bottom of dash just below glove compartment.

• Apply new sealant to the heater core cover and reinstall.

• Next push the AC/Heater box back against the firewall and replace the two nuts on the firewall in the engine bay to hold the unit in position.

• Reconnect the heater lines in the engine bay and fill the radiator with water.

• Start the car allow it to warm up and check for leaks. If no leaks are found, finish reinstalling everything as it was before and drain and refill your radiator with antifreeze.

Below is a break down on the entire AC/Heater box.

Non-AC Equipped Mustangs:

• Drain the antifreeze from the cars cooling system VIA the drain cock on the radiator. Note: f you do not have the drain cock release the fluid through the lower radiator hose.

• Disconnect the heater core water lines from the heater core tubes protruding from the passenger side of the firewall in the engine bay.

• Remove the glove box from the dash. Three screw from bottom of dash just below glove compartment.

• Locate the heater core cover panel located directly behind the glove box opening.

• Remove all the cover bolts.

• Once the cover panel is removed remove the heater core from the Heater box.

• Clean up all factory sealing goo off the cover area and Heater box.

• Practice how you will get the new unit into the Heater box using the old damaged unit.

• This way you know the best way to get the core in there without damaging it.

• Once you feel comfortable with your process of installing the new core, do so taking extra care not to damage the new heater core.

• Apply new sealant to the heater core cover and reinstall.

• Reconnect the heater lines in the engine bay and fill the radiator with water.

• Start the car allow it to warm up and check for leaks. If no leaks are found, finish reinstalling everything as it was before and drain and refill your radiator with antifreeze.

Below is a breakdown of the entire heater box assembly.