Replace Heater Core 1971, 1972, 1973 Mustang
#1
1971 1972 1973 Mustang Heater Core Removal

1. Disconnect Heater and AC hoses. (See manual on proper AC disconnection procedures.)

2. Cut drain hose from under car at bottom of firewall. You may want to save the plug that’s inside the end of the drain hose, which is there to prevent critters from entering your heater box. Note: If you bypass this step, you will likely break the fiberglass drain nipple off your heater box trying to pull it out.

3. Remove glove box door and glove box insert.

4. If you have a camera, take a picture of the vacuum hose and temperature control cable area now before disassembly. Label hoses to further aid in reassembly.

5. Disconnect: Thermostat switch wires; vacuum hoses to heater box (2) vacuum canisters; vacuum hoses to (cable controlled) water valve switch; and cable to water valve switch.

6. On the engine side of the firewall, remove 2 heater box hex/washer nuts. Easily identified by large washer and long protruding studs.

7. Remove 2 blower motor housing retaining screws (under dash center) and permit blower housing to hang (no need to remove the firewall mounting on the blower motor).

8. You may need to remove the vacuum canisters to give the heater box assembly some wiggle room during removal and installation.

9. Remove the heater box to cowl retaining screw (look up at right side of heater box).

10. Remove heater box assembly by sliding to the right (to disengage the blower fan), then down.

11. On the removed heater box, put a large screwdriver blade in the return of each metal spring clip such that you are opening up the springs to remove them. Do NOT pry the clips off by inserting the screwdriver under the clips – This will permanently damage the heater box.

Reverse to install.

Though some of the above is not included in the shop manual, if you need more info. (such as diagrams), I strongly recommend buying the full shop manual set.
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#2
These instructions could come in handy. My 73 Convert still has the original heater core! Only 110k miles but it is old! Thanks
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#3
Great information i've been stuck for the last couple of days on this problem.
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#4
(01-10-2012, 07:43 AM)Jcyr Wrote: Great information i've been stuck for the last couple of days on this problem.

Let us know how it goes or if you have any thing to add to the tips above.
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#5
Thank you for the great information. I bought the manuals but like you said they do not cover all that you need to do. I have been trying to replace the heater core and was having trouble. Appreciate it.
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#6
I also like to remove the passengers seat, it makes for more working room and less of a need to be a contortionist
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