Good old Bill

If the coolant isn't leaking inside the truck (no smell or wet floor) your leak could be the water control valve located in the lower hose of the picture. Its the little thingy that has the vacuum line attached to it. They are not repairable, has to be replaced.

Ranger2F150

The heater core should be replaced. The reason: it helps the evaporator coil to keep from icing up. You will still have fresh air coming thru but will not be enough to prevent this. Temporarly disconnect hoses with a coupler you can find at parts house. Make sure of inside diam. of hoses some are 5/8 and 3/4 you will need a hose adator to fit this "they do make them".

Hope this helps you figure it out.

Ranger2F150

agree this could also be the problem.

scubasimmons

Good point about the AC evaprotator icing up. I glazed right over the truck having AC.

The heater core on my '83 (only an XL) went out and I only got a faint smell of antifreeze once in a while and there was never any fluid leaking inside under the floor mats (the bottom of the heater core housing sat below the fire wall pass through so there was a lip keeping the fluid out. Finally the heater core failed catastrophically and there was antifreeze everywhere under the the truck.

To bypass the heater core, completely remove one hose and disconnect the other hose from the heater core and plug into where the other hose was (non heater core side). I'm more of a Macgyver mechanic (know just enough to make it work whether it is correct or not and using the chilton manual), so if it was me I'd leave the hose with the water control valve since I don't know what it does. Or you can buy an adapter to couplke the hoses as stated above if you plan on replacing the heater core at a later date (sounds like it may be the best option so you don't compromise your AC unit).