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This is a very involved process that I could not begin to express here how its done. Check with your local library for a Chilton's repair manual or comparable service manual so you can get very guided details including pictures.

Mcgyver331 added:

This is no fun I am doing this as I am writting today.

First you have to remove the dash. There are various 10mm bolts and Philips head screws.

There are wiring clips on the radio, the headlight switch (there is a button in the rear of the headlight switch to remove the switch rod)and on the gauge panel for easy removal.

Then I would suggest you remove the internal engine cover for easier access. That takes a 1/2in. socket. There are 2 hoses to the left side of the engine bay. You can see those clearly if you remove the air intake rubber duct. The upper hose has the heater control valve on it and the lower one is a return line. These will need a flat head screwdriver or a 10 mm socket to remove the hose clamps.

I am right now trying to remove all the corresponding duct work to free up the heatercore box.

I removed all the duct work, then I found that there are a few bolts that go through the firewall to the a/c box on the engine compartment side. remove the 3 nuts and there is one bolt on the inside right hand side. There is a bracket that holds the dashboard bottom remove that also with 1/2in or 13mm.

Finally the heater box can be removed. you need a 1/4 in socket to split the heater box. there are like 15 little bolts for this. once the box is split you will finally see if the heater core is bad.

I started at this point to split all the duct work in half and clean it with bleach. Once that was done I replaced everything.

work slow if you rush disasters with wiring and vaccum hoses can occur.

thanks for reading

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โˆ™ 2011-09-12 20:44:25
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Q: How do you replace a heater core on a 1990 g20 Chevy conversion van?
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