How to replace heater core on Toyota previa?

Remove the side cover from the right side of the HVAC box on the floorboard under the center of the dash. It is the big black plastic console under the center of the dash up against the firewall. You'll be able to see the heater core once you remove the side cover. It is copper or brass in color and has two tubes running through the firewall into the engine compartment. You cannot remove it as easily as it looks because the control linkage is in the way. The pipes running through the firewall block it from being able to slide out and the glove box hangs down and obstructs it from sliding out more than a couple of inches anyway.

Here's what you do: Disconnect the bottom hose from the heater core on the other side of the firewall. Antifreeze will start to pour out as soon as you remove the hose so have a bucket ready to catch it. Now disconnect the top hose and use a garden hose to flush out the heater core through the top pipe. Once the water runs clear you can turn off the hose and move on. You do this in the event that any fluid spills inside of the van later. Antifreeze is sticky, it stains auto carpeting and it has an odor to it as well.

Now back inside of the van remove the control rod and the linkage plate that blocks the heater core from sliding out of the HVAC box and remove the pipe clamp that holds the pipes in place. If there is any water left in the heater core you will most likely need an empty bowl for the next step. Take a Dremel (or other rotary tool) and using a metal cut off wheel cut the pipes off of the heater core about 1 1/2" out from the side. Once that is done remove the cut off pipe pieces and throw them in your recycling bin. At this point you still can't slide the heater core out because the glove box is in the way.

Here's how move forward: Remove the glove box lid and then remove the two bolts at the back. There is an electronic control module behind the glove box that the bolts went into. It will most likely slide down after it is unbolted. Next use a small flat screw driver to remove the right corner piece, which is part of the vent system and just pops out if you do it right. Next there are two screws located just under the bottom lip of the dash that hold the front of the glove box to the dash. You'll need a stubby Philips screwdriver to get them out and will most likely need to lay upside down on the floorboard to unscrew them properly.

Take your Dremel in hand and cut the interior of your glove box in half horizontally, which is pretty much right at the middle of the two bolt holes in the back. Cut the glove box from where it hits the dash on the left around the back to the part that you popped out earlier and then on the other side to the dash. Next pull out the bottom part. You might have to twist it a bit to get it out.

Don't worry you can pop it back into place later and the bolt in the back and the screws in the front will support it and all you'll need to do is run some black duct tape or Gorilla Tape around the cut.

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Now with all of this done all you have to do is slide the heater core out. To replace it you need to buy about three feet of 3/4 inch heater hose and four appropriate size hose clamps. Obviously you'll need the new heater core as well. When you have these things take your nice shiny and new $175.00 heater core and cut the pipes off of it with your Dremel leaving about 1 1/2" of straight pipe at the side. By the way Kragens Auto (AKA Schuck's or Checker Auto) can get you a heater core for $126.85.

Now use a grinding bit or a deburring bit or sandpaper to smooth the cut pipe edges out. Install the new heater core by simply sliding it in place making sure you move the flap that you'll see in the slot back. Now all you have to do is run heater hose through the rubber grommet in the firewall to the heater core. You can use some epoxy inside of the hose ends to insure a good seal and cinched them down with hose clamps.

Hook the hoses up on the other side and then reattach the linkage you disconnected earlier and cut the side cover from the HVAC unit with your Dremel in order to fit the new hose routing.Cut it just above the edge where it turns up. That way it protects the hose ends from getting kicked by your passenger. Then install your glove box, screw and bolt it in place, tape the cut you made in it and check your coolant level after you start and warm up the vehicle enough to run the heater.

If you ever have to replace the heater core again it will take you about 45 minutes to an hour tops.