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Instruction: Heater Core Removal - '80-'87 K5 Blazer


Tom Lasco
02-12-2004, 02:51 PM
Last Weekend, I requested some advice on removing my leaking heater core. Now that I have successfully removed the heater core, I would like to provide a detailed account of how to do it while the experience is fresh in my mind. By the way, the cause of my Heater Core failure was corrosion in the body of the heater core. The in/out tubing was still in good shape. I am wondering if this corrosion could be due to the fact that the Heater Core is not grounded which could be causing a electro/chemical reaction between the antifreeze solution and the metal of the Heater Core.

I read somewhere that GM hung a heater core on a string and built the Blazer around it. That's a good description. Here goes:

1. Remove the glove box. (15 min)
2. Drop the wheel well. This is a dirty job that is necessary only to expose one Stud Nut in the engine compartment which holds the heater casing that houses the Heater Core. The bolts on mine came off really hard. I even broke a socket. (2.5 hrs.)
3. Remove 3 Stud Nuts from the engine compartment opposite the Heater Core Casing. One of these stud nuts cannot be removed unless the wheel well is dropped as in step 1. This stud nut is located on the left side of the firewall under the fan motor housing. The other two stud nuts are located next to the top right side and bottom right side respectively of the a/c evaporator case. I also had to open up the evaporator case because it was overlapping a screwplate which was under the stud nut at top of evaporator case. The other two stud nuts did not have the screwplate. (2 hrs.)
4. Inside the vehicle, remove bolt on right side of Heater Case in passenger side under glove box. ( 5 min.)
5. Remove the heater/ac selector control cable from it's guide on top of the heater core casing. You must also remove a bolt on top of the casing which secures the left top side of the casing to the under side of the dash panel. (15 min.)
6. You are now ready to carefully dislodge the heater core casing inside the vehicle. Be gentle because there are two vacuum hoses still attached to the top of the casing. You can partially remove the right side of the casing to gain better access for removing the two vacuum hoses. (10 min.)
7. You are now ready to take the heater core casing to a work bench. Essentially, you must completely disassemble the heater core casing to gain access to the heater core. I fooled around with it for about an hour before I got everything disassembled to finally remove the heater core. (1 hr.)

Final Thoughts: As it became clear just how big a headache this job was, I had an idea that I could save a tremendous amount of time and work, it there was a removeable panel on the front of the heater core casing. If this were true, you could remove the panel and gain immediate access to the heater core. Now that I have removed the heater core the hard way, it seems that this would have been a simple way to do this job. GM could easily have designed the heater core casing similar to the a/c evaporator casing with two clam shells held together with several screws.

Note: The times given for each job are somewhat longer than they should be due to the fact that I did this work in a public underground garage with poor lighting and with minimum tools. In a proper work environment and full set of tools, you could cut the time by 30%-40%.

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