73-79 F Series and 78-79 Bronco

Heater Core and Heater Motor Replacement

For Trucks with Factory A/C or Hi/Lo Heaters


GDI by Proliance 399022 Heater Core


This is what the Unit Looks like

Also if you have Removed this cover you basically Ruined your Unit

Step 1.

Remove the two  5/16" screws and cover in the picture below this is up by the Firewall on the Housing

(Note this does not apply to HI/LO heater no need to remove this cover)

unit with A/C line cover Removed and gasket pull out of the unit

Heater Hoses Removed


The cover under the dash that is removed

Step 2

Remove this boot From the Cover

Step 3

Locate and Remove 4 Nuts and one bolt that secures the cover to the Firewall And disconnect this Vacuum Hose from the Cover

Note the Position of the 5 holes in the cover

Step 5

Remove this Duct it goes to the far right Vent it is just clipped in

Step 6

The Thermocouple needs to be handled with Care and must be removed from the evaporator

Step 7

Remove the Evaporator and side panel Screws

Step 8

Pull Bottom of Evaporator out and Secure as close to the Dash as possible

Heater Core is now Visible it is secured with 3 screws and 2 brackets

Heater Core removed from Unit

Very Carefully Remove the Gasket from the Core as you will need to reuse it with the new core

If only Replacing the Core the following Steps does not apply simply reverse the above steps and put you unit back together


If replacing the Heater Motor then continue with the Following Steps

Step 10

This is a little more involved but still not over whelming

Remove the blend Door

The Blend door removed showing the location of the mounting holes

Pry the control Arm from the door

Step 12

Remove Heater motor Screws

If you have the A/C Evaporator you will probably need to remove the Squirrel Cage while it is in the unit as the heater motor and cage assembled will not clear the evaporator

using a Long 1/8" Allen Wrench to loosen the Set screw on the Cage

then remove cage from motor

Heater Motor and Cage separated in unit and removed

Reverse order of steps when installing new motor

estimated time under 4 hours for first time R&I



The New Parts and Part numbers

Old Motor Compared to New Motor

Some minor differences but nothing that is detrimental to the install

Note the Motor Turns Clock Wise  as you look at it in the picture

make sure the new one is wired to make it turn clock wise


Cut the original harness off the old motor and install it on the new motor