You don't have to remove the plenum box with the HeaterTreater fix. Follow the links below for a complete answer.
The Heater core is difficult to replace on the F150 since it is buried in the plenum box. Getting to the core involves removing the steering wheel, steering column, complete dash panel, evacuating the AC, draining the radiator, and finally removing the heater box. Once you have the box out(8-12hrs), the core is simple to replace.
You want to be sure that the core is the problem before you undertake this process. If there is a strong smell of antifreeze in the cab or a puddle of coolant on the floor, the diagnosis is easy.
Check that the radiator is full, not the overflow tank, the radiator. On a cold engine you can remove the radiator cap and check the level. It should be full. If there is air in the system it will affect cab heating and engine cooling.
Another good check is to feel the two heater hoses going into the firewall from a cold start. The hoses should warm up at about the same rate and get uncomfortably hot-close to radiator temperature.
If the core appears to be OK, the next concern is with the blend door that diverts air through the heater core. This is a common failure on the F150. We have a video posted on our web site that shows how to diagnose and repair the system. Please follow my user name back to my bio page to find a cut-and-paste link to the web site. You are only a few clicks away from solving the problems.
To replace the heater core in a 1999 Opel Astra, remove the center console and remove the 6 5.5 mm bolts. Also remove the clips and remove the cover and plastic clips on each pipe. Finally, lift the heater core and replace with new.
You have to remove the entire dash board to gain access to the heater core.
The heater coil is located behind the dash board. You will have to remove the dashboard to get at the heater coil
You will need to remove the water lines from your heater core. Remove the heater core retaining bolts. Reverse the process to install the new heater core.
buy a Chilton manual and it will tell you most of what you need to know.
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With difficulty. Tried to remove the one in my 1997 and found that you really do have to remove the entire dash to access it. If you have it out already, try to get your hands on a new heater box, saves the hassle.
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