So - your heater core is leaking?

Nasty bugger of a failure which will announce itself by the smell of refrigeration liquid. Now you hopefully have anti-freeze in it or you won't find out until one of your passengers complains about hot water dripping on her or his feet. A wet carpet might also be an indication but is not conclusive, as two out of three times this happened to me, the water seeped down between the firewall sheet metal and the carpet to soak the insulation.

That means if you are filling your cooling system regularly but have no patches of water under the car or it is not clear if leaking into the engine or somewhere else this might be the moment you want to pull that carpet under the dashboard on the passenger side and have a look.

Now to the business of removing this masterpiece of engineering without disassembling your dashboard. The screws have been put so ingeniously as to wonder if someone did that on purpose to create so much trouble.

The first part is the quick remedy to the leaking itself - and if you are lucky it happens to you in summer. The hoses are located on the right hand side in front and below the blower motor. The idea is to bypass the heater core altogether in the engine bay to stop the leaking but still being able do drive your Blazer. I had to cut one cable binder next to the air conditioning accumulator to get the wires and the hose from the vacuum accumulator out of the way. On the 1994 you can simply pull the connector of the brown wire to the blower. Now you can access the two hoses to and from the heater core.

WARNING: Do this with the engine cold and stopped! Do not run the engine during the whole operation of putting the bypass in. We are dealing with hot water here (if you cannot wait for it to cool) and some pressure which might still be in the cooling system. So let it cool as this eliminates the pressure and saves you scalding and a big mess.

Oh - and of course you need a "bypass" beforehand. As I have access to a turning lathe and found a nice piece of aluminium about 80 mm long (make it 3 1/4") and 20 mm in diameter which are something like (13/16") I put that into the mill and started cutting my way through the metal. Half way down I found that I had forgotten to put a thicker end to it in order for the hose not to slip from it when the cooling circuit heats up and produces pressure.
PICTURE #1 and #2
That is the reason for picture #1 and #2 the two ends being different... shame on me. Nevertheless it works. Now you might wonder why on earth is this crazy milling himself such a bypass as one could use any kind of tube. The answer is twofold. First because the engineers have been very creative and came up with the amazing idea to make the two tubes of the heater core two different diameters.
Yes, I know it makes sense somehow but is a pain in the a... when it comes to fix it. The diameters are roughly 16 mm (5/8") and 19 mm (3/4"). Forgive me for being a child of the metric - we might never understand your measurements. Second because I need some practice on the turning lathe.
One screw holds a bracket to the blower casing which supports the tubes from the core. Unscrew and remove - or have it fall into the case as in my case .
Then use pliers to pry open the brackets and push them back on the hoses. It depends if you can accept the mess under the car from some spillage of cooling liquid, you may or may not put a bucket under the car just inside of the right front wheel. Pull the hoses from the copper tubing of the heater core now. It may be necessary to turn them to loosen them on the tubes, pull them off and place upright to stop them from spilling. They can be conveniently held against the valves of the A/C accumulator.
Once both are off put your bypass in place have the hoses fold back more or less into the normal position and make sure they are not kinked, else by turning them against each other a good position can be found. Now put the brackets back on. Have the hoses fixed with a cable binder somewhere convenient.
PICTURE #3 and #4.
Fire up the engine and check if the bypass is leaking. If not if it leaks redo your bypass until it's watertight.

Depending on your location you may want it fixed ASAP or leave it like this if you live in AZ or similar. It keeps the passengers feet cooler

For those wondering why I went through all the trouble with a bypass instead of just plugging the two hoses - because I don't know exactly how the cooling system would react to two relatively important ducts being plugged as previous experience with other cars has shown this to be a very sensible system. What happens in the water pump? What happens where the discharge hose connects to the head? Would it build up heat there because we have no flow now in that area? So instead of an experiment - a bypass.

Now to the interior and the big question - can I remove the heater core without unbolting the whole dashboard?
For once does not really help because it goes for a lengthy explanation on what you have to unbolt to get the dash out to conveniently get to the heater core (4 1/2 pages with 2 pages of illustrations - so much for removing the dash). So you save yourself some bit..ing with the heater core but have a lot of fun with the dash itself. After reading the service manual I put it aside and started unscrewing and unbolting the covers on the passenger side. Remove the 4 screws on the right hand panel in front of the door opening. Unscrew 5 screws located from below the dash and remove the two pieces of cover from underneath. Now you can access the screws on the heater core cover. But only the three lower ones are easily accessible while the two top ones are . So I had a lenghty fiddling with a small mirror and came up with the following solution.

Open your glove box and empty it. Then remove the small cover at the back. Now drill a hole into the glove box lower right corner as can be seen on picture #5.
PICTURE#5
Make the hole big enough to get a 1/4" nut with a long extension through it. Loosen the screw in the top right corner of the cover.

The second screw can be accessed through the ash-tray which has an opening in the right lower corner as can be seen on picture #6. Yes it is a good place to fumble your 1/4" nut with a very long extension through as the stuff behind the ash-tray box are mere wires and hoses which can be pushed aside. You may have to guide it onto the screw by fumbling through the glove box.
PICTURE#6

Once that is gone you should be able to wiggle and pull the heater core cover. It may need a decisive pull but be gentle as you do not want to brake it too badly else the warm air may never reach the intended places again. But then at this point of exasperation one might even brake something... High speed tape may be the remedy afterwards.
I got to the point where a job with a saw on the dash became an option...
PICTURE#7
Now you should be able to get to the retainer screws holding the heater core in place. I had only the two lower ones removed the last times (once about 5 years ago and once about 12 years ago) and had the brackets turned a bit outwards to wiggle the core out. Before you do that go looking for a cork to cut in half and put onto the core tubes. It helps keep the water level in the passenger bay low.

Some sidenotes: It is not necessary to remove anything from the glove box except for the small cover in the back. I could not remember if I had to remove the frame and door or not just to find out that: No it is not necessary! So I ended up with all these parts removed as in picture #8.

I'll do some thinking because if this car continues to last as it did I may have to replace it again. And then there is my second Blazer which may need the same thing. So I'll keep my bypass this time.

I'll also put some thinking into a modification for a quick fix to remove the cover and some more thinking into my project Blazer to have the whole A/C heater stuff put into the engine bay to make a neat hot/cold mixing chamber of sorts because me thinks it cannot be so difficult for a dedicated person to come up with better solutions. I'll get back with that.

So now I have a writeup which will help the next time I have to get through this. I'll be back and add more pics of the repair and how to put it back in.

Hope this helps and feel free to add your experience and comments.

 

The heater core is a pain in the butt to change. After taking off all the bolts and screws, then pulling the dash out far enough to get to it, I just put the necessary bolts back on and a couple of screws that were easy to get to so I wouldn't have to try to get the screws that are up under the dash for the cover back off.