Here are some steps to replace the heater core in your 1979 Ford F250 Custom Pickup: (1) Disconnect the battery ground cable. (2) Remove the air cleaner. (3) Drain the engine coolant below the level of the heater core. (4) Remove the heater hoses from the heater core. (5) Remove the screw fastening the A/C hose support bracket to the firewall. (6) Remove the insulating tape covering the valve. (7) Remove the two screws holding the plate over the opening that the A/C hoses exit the evaporator housing. (8) Remove the plate and the seal. (9) Remove the glove box liner. (10) Separate the A/C duct from the register in the instrument panel and free the clip holding it to the plenum. (11) Remove the duct from under the dash. (12) Remove the vacuum hose from the vacuum motor on the right-hand side of the airbox. (13) Remove the rear housing cover from the evaporator housing. The cover is retained by 4 nuts and one bolt. (14) Disconnect the fresh air tube from the rear cover. (15) After removing, reinstall one nut...

Here are some steps you can try to remove the retaining pin: (1) Apply Penetrant Oil: If the pin is stuck, spray it with some penetrant oil and let it sit for a few minutes before trying again. (2) Use Tools: You can try gently tapping them with a hammer or using a pair of needle-nose pliers/wrenches to pull the pin out from the backside of the caliper. (3) Heat and Beat: If the pin is rusted and stuck, you might need to apply heat to the area around the pin and then tap it out. (4) Vise Grip Method: Another method is to use needle nose vise grip clamped onto the pin from the rear as tight as you can get it. Then give the handle of the vise grip a tap with a hammer and the pin should loosen. Please remember to be careful when working with these components as they can be under high pressure. If these methods don’t work, it might be best to consult with a professional mechanic. As for the frozen caliper, it’s possible that the caliper piston is seized. If a C-clamp isn’t working to retract the piston, you...

1973 ford truck shop manual: https://www.fordshopmanual.com/ford-truck-shop-manuals/1973-ford-truck-shop-manual-pdf-download/ 1973 ford truck parts catalog: https://www.fordshopmanual.com/ford-truck-parts-catalogs/1973-1979-ford-truck-parts-catalog-pdf-download/