The Stovebolt Site Forums The Parking Lot Big Bolts heater core and defroster connections

It seems that every repair to my 66 GMC 5500 truck leads to finding another problem. Working on the rusty floorboards led me to find a leaking heater core. Removing the heater core required taking out the entire heater/blower control box. This turned out to be a good thing as I found mouse nests in and above the box and discovered some missing parts. I know that this isn't a super interesting topic, but could use some help with getting things back together in a way that works.

New problem 1: Now I need to replace the heater core, but can't find one that fits. The core "radiator" needs to be 9 1/2" high, 7 1/2" wide, and 2 1/2" deep. This is bigger than the easy to find pickup heater cores. Any suggestions on where to find a new one? Otherwise, I will need to take my chances on having the leaking core rebuilt.

New problem 2: After removing the heater/blower box, it is obvious that the piece coming out of the blower that connects to the defroster tubes (and more?) is missing. (I never thought about or looked for a piece missing in the middle.) Does anyone know where to find something like this or what it looks like so I might have some idea about how to build a replacement?

Possible new problem 3: There is a large tube on the driver's side under the dash (below the smaller defroster duct) that could either be an outlet or should be connected to another missing piece. Can anyone tell me what this is?

My goal is to have a working ranch truck. This includes being able to use it in the winter and seeing out the windows without having to be wiping them with a rag. Any help would be appreciated.

After taking parts out of the way under the dash and tracing control cables, I find the heater problem is not as bad as it looked at first. The defroster distribution and control comes from a box on the other side of the cab that is over the accelerator pedal. What is missing is about 3 feet of large ducting that moves air from the blower to the distribution box and the piece connecting to the blower that converts the square exit to a round duct. I can make this if it can't be found elsewhere.

I am still looking for a heater core and will put up another post about this because I can't be the first truck owner looking for a larger than standard core.