The other source of heat is from the heater core which always has hot water in it. Some air will make its way through and carry heat into the car. Some people put a shut off valve to cut off the hot water to the core.
The other source of heat is from the heater core which always has hot water in it. Some air will make its way through and carry heat into the car. Some people put a shut off valve to cut off the hot water to the core.
My 69 had a water shutoff valve on the wheel well for the heater so water did not flow through the core all the time
All A/C cars should have the valve to keep the hot water from circulating in the heater core. If you don't have that, the repop them, but good luck finding the bracket that mounts it to the wheel well. That is a unicorn if you can find it.
Another good size hole is for the 4 speed clutch rod, quite often the boot tears and pores heat thru. I would most certainly guess you will need a new one. They all tear.
All A/C cars should have the valve to keep the hot water from circulating in the heater core. If you don't have that, the repop them, but good luck finding the bracket that mounts it to the wheel well. That is a unicorn if you can find it.
Added for the '69, GM should have added a '67-'68 technical bulletin offering the valve as an additional cost dealer-installed option for both the AC '67's and '68s as well as all non-AC first gens when owners complained about cabin heat. If I used my AC anymore I would add the valve, correct or not.