My 78 lariat started leaking from the air box drain tube, I knew it had to be the heater core. Let me tell you, that was a chore to get apart. The whole heater box must come out from under the hood and the a/c evaporator has to be removed from the box to get to the heater core. I noticed my evaporator was turning green and rotting at the bottom too, so I replaced it too. The heater core was only 30. bucks, but the evaporator was $300.00 !!. Just got her back together today, no leaks and ice cold a/c. (I had some R12 laying around from the good ol days) Boy am I glad to be done with that!
Non a/c trucks are easy, beware if your truck with a/c starts leaking from the core.

 

guess thats what I have to look forward to if mine ever fails! Lucky that you had R12 around. I've heard its still available in mexico...

 

Yep, that's one of my least favorite repairs ever. I did mine from inside the cab.

 

Thats what I've heard. I changed the heater core in my non-AC 1977 and it was easy. My uncle has a pretty decent 1979 F-150 Ranger with limited slip front and back. It is an AC truck and the heater core started leaking probably 10 years ago. He just stopped driving it! I think he got it runing about a year ago and apparently one of the valves was sticking from old gas and it bent a push rod. Wow, I think that one is about done for. Its a tutone red and sliver, nice truck.

 

Heater Core Removal and Installation For 1973-1979 Ford F-Series Trucks .: Articles

 

It's actually very much available in the US, too. The price has also dropped dramatically in the last few years. The last #30 cylinders I bought were $300, that's $10/lb. Just about the going rate for R134a.

 

Where do you get it from? I need to restock for some other old vehicles I've got.

 

My heater core went bad several years ago and got an estimate for replacement at $600. I decided to just do it myself. I did it through the inside. NEVER again. After six hrs. of that crap I would have been happy to pay.
As far as my a/c goes it has never cooled correctly since swapping to R134.

 

Ebay and Craigslist.
A lot of folks still think it's liquid gold, but if you're quick you will catch the deals. I recently missed a sealed #30 jug for $200 by about an hour on CL.

 

Sorry but that is incorrect. I have replaced the heater core and the blower motor in an A/C equipped 79 Bronco and took neither of those items off to do it. While it is not the easiest job to do it is not necessary to remove the box from the firewall.

 

I think through the inside or pull the box sucks about equal. I had a hard time getting the whole box out and back in, but switching the parts was easy while it was laying on the bench.
Hopefully neither of us have to do that job again!

 

Your right, you can do it from the inside. I don't think it's any easier either way, but I GUARANTEE you have never changed a heater core without pulling the evaporator on an a/c truck..

 

Mine just started leaking after I put the 466 in it. Non-AC though...

 

there may be differences between factory air and dealer installed air, too....

 

Yes there are. Dealer installed air is much easier IIRC.