Remove all the 13 screws holding the upper and lower housings of HVAC unit using 5/16 nut driver. This pic shows the two of them on the blower fan side.
Two screws near the heater/AC lines are shown.
One screw right next to the heater lines is shown.
Two screws near vacuum pumps are shown (opposite side of blower fan).
Another screw near the vacuum pumps.
More Heater Core Replacement
4x4 Off-Road Homestead Firearms RC Flying