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Old 11-16-2008, 07:07 PM   #1 (permalink)
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Help --> Replacing the heater core

('96 Trooper, 3.2 liter, sohc, manual trans, A/C.)

Hi Folks,

When I last used the defroster, I got the classic bad heater core symptoms like, it seemed to add fog to the windshield instead of clear it, plus defroster air smelled like coolant.

First, is there any chance this is caused my some other non-heater-core-gone-bad issue that's easy to fix?

OK, so at this point, I've got left and right lower dash items and dash frame pieces pulled. Shifter part of the center console stuff out of the way. Coolant drained from the engine. Heater hoses disconnected from the engine.

I'm guessing I've got to take the central section of the dash out, the part that extends from the heater controls down to the floor and includes control computers, etc.

It looks like once I get all the junk out of the way, I might be able to take down the left half of the whole heater-AC conglomeration, leaving the AC evaporator still connected, in tact, and relatively undisturbed (perhaps at worst left hanging off the fire wall, but still connected, etc.).

Is that right? Or, will I have to let the freon out and disconnect the lines to the evaporator and pull the whole heater-AC conglomeration out together?


Helpful tips from someone who's done this one before would be greatly appreciated.

Thanks...

PS: The good news is, in the process of taking down all the dash stuff, I found where the PO had his alarm/keyless entry gadgetry installed, so perhaps I can get that working again. Keyless entry would be neat. I could care less about the alarm working.

Last edited by Rude_Dog; 11-16-2008 at 07:09 PM. Reason: make sure I was subscribed to the thread.
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Old 11-19-2008, 09:36 AM   #2 (permalink)
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I've never worked on a Trooper but replacing a heater core should have nothing to do with freon or evaporators. Should be strictly under the dash stuff but definitely a PITA.
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Old 11-19-2008, 06:45 PM   #3 (permalink)
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Well it is so that you have a bad heater core..the "fog" on the inside of the window, with maybe some sweet smelling antifreze on the p-side floor...yep...good luck with that. as for relocating a heater core, ya right. you are forgeting that the heater core is built into the middle of the blower box assembly...( yes I know how it is spelled) It is a pain in the ass to get to.
Enough said,
answer your question, no you can't do it if you still want a heater or AC that work.
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Old 11-19-2008, 10:03 PM   #4 (permalink)
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Yes, PITA indeed. Thanks for your consolation, but I had hoped for a reply from someone who has done a heater core R&R on a 96 trooper or similar.
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Old 11-19-2008, 10:09 PM   #5 (permalink)
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Quote:
Originally Posted by smith123isuzu View Post
answer your question, no you can't do it if you still want a heater or AC that work.
I'm sorry, could you clarify? When you say no you can't do it, are you saying I can't just pull the left bit leaving the evaporator and blower section behind, so I don't have to mess with disconnecting the AC lines?

Thanks
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Old 11-19-2008, 10:29 PM   #6 (permalink)
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I haven't done it on a Trooper as yet but, on a '94 Rodeo (lot's of similar parts) you have to remove the A/C unit BEFORE you can get to the heater core... and yes, pain in the.... etc.
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Old 11-20-2008, 12:36 PM   #7 (permalink)
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Quote:
How do you replace a heater core on a 94 Isuzu Trooper?
In: Isuzu Trooper

Answer

Wow, what a chore you are about to get envolved with! You must remove almost all of your dash including the center. I have a diagram of the bolts you need to remove if you want it. Goodwill1971@hotmail.com. Next you will need to start removing the vents and other parts of your AC system under your dash. Your heater core is inside the front part of the blower box. First you must disconnect the hoses inside the engine compartment on the passenger side where they enter the fire wall. After you remove the entire black heater unit from under the dash you will be able to see the core just below the flap. You must carefully separate the blower box into its two halves to remove the core. The hardest parts are getting the new core back throught the fire wall (I enlarged one of the holes) and making sure your cables from you ac control are adjusted correctly. Sorry this is not a very technical discription.
Quote:
What is the easiest way to replace a heater core in a 1992 Isuzu Rodeo?
In: Isuzu Rodeo

Answer

The easiest way is to have some else do it!!
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Old 11-20-2008, 05:17 PM   #8 (permalink)
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Quote:
Originally Posted by lttlbddy View Post
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Nice work, lttlbddy. The description of changing the heater core on the 94 trooper sounds very similar to what it appears I'll have to do.
Quote:
After you remove the entire black heater unit from under the dash you will be able to see the core just below the flap. You must carefully separate the blower box into its two halves to remove the core.
This answers my question where I was wondering if I could take only the left half of the unit down, leaving the AC part behind. Apparently the entire heater-AC-blower unit has to come out, then get separated to get the heater core out.

This just means there'll be the added headache & expense of getting the AC system evacuated and recharged with freon once I've got everything else back together. Oh, well, at least now I sorta know what I have to do. I probably should have driven my Trooper to a shop and let them suck all the freon out before I started. Now it's too late.
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Old 11-20-2008, 05:27 PM   #9 (permalink)
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Originally Posted by Stuntopts View Post
I haven't done it on a Trooper as yet but, on a '94 Rodeo (lot's of similar parts) you have to remove the A/C unit BEFORE you can get to the heater core... and yes, pain in the.... etc.
Yeah, it's lookin' like it's the same for the trooper.

Thanks.
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Old 11-21-2008, 08:58 AM   #10 (permalink)
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yes you can leave the ac unit in the corner, unbolt it pull it out of the way, with a little finess you can get the core out then back in. just don't break the plastics
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Old 11-23-2008, 08:53 PM   #11 (permalink)
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OK, tonight I finally got the heater core out in my hands. Oh, man, what a cluster . I got the dash and just about everything under it out in order to get to the darn thing. Here are some hints for anyone who's about to attempt this.

1. First thing first, if you think your Trooper needs a heater core, seriously consider whether you really want to keep it around for a while, because it might be more worth your while selling it to someone who's not going to worry about whether the heater/defrost works, like a rock crawling aficionado, or perhaps to some ranch to be used as an unregistered farm vehicle or some such. Or, seriously consider disconnecting the heater hoses from the heater and just running a bypass from one pipe on the engine to the other, in case you live somewhere warm and you can do without the heater. Upon reflection, this is a pain in the butt job that I wouldn't wish on anyone.

2. The whole conglomeration comes apart in three section, heater (left), AC evaporator (center), and blower unit (right). The three sections aren't actually fastened to each other, they're just fastened to the firewall next to each other.

3. After pulling the front center console/shifter bezel, dash (don't bother pulling the instrument cluster from the dash, it comes out with the dash.), and almost everything under it, and after draining the engine coolant and disconnecting the heater hoses from the heater core ports that protrude through the firewall, you can remove all of the nuts that hold the whole conglomeration to the firewall.

4. To get the heater assembly out, I found I had to remove the blower assembly first. This gave me the room I needed to slip the AC evaporator portion toward the rear of the cab, and then gently bend it slightly to the right toward where the blower was. This gives you the needed clearance to pull the heater away from the firewall (the heater hose connection ports go through the firewall to the engine side and make an immediate 90 toward the right, so the heater has to come away from the firewall left end swinging out first in a sort of rotating move, which is what necesitated the shifting of the AC evaporator to the right, which is what necessitated the removal of the blower unit).

5. To get the blower out, I found I didn't have to completely remove the ~2" diameter support tube cross member thingy, but I did have to take out the right side mounting bolts so I could wiggle the cross tube around a little.

6. On the engine side of the firewall, the AC lines rise away from the firewall several inches before they make a 90 turn to go through the firewall to the evaporator. You can use this extra length between the 90 and the firewall to pull the evaporator unit rearward and bend it slightly to the right.

7. Once you get the heater section out and in your lap, take off the left end of this section, then split the main part of the heater case. There are several screws around the periphery of the case, and a central screw down a deep crevice.

When I got my heater core out in my hands, I was a bit disappointed because I didn't see any clearly identifiable signs of leakage on the core itself . However, the two 90 heater hose ports connect to the heater core using an O-ring'd 2-bolt flange. When I removed them, the flanges and O-rings seemed kind of wet, so maybe that's where the leak was, or maybe they just got wet as I was taking things apart. Now that I'm thinking about it. It might have been wise to leave the hose connection ports attached to the heater core and then rig up a way to pressure test it. Maybe cap off one port and apply light air pressure to the other port and then submerse the whole thing in hot water and look for air bubbles?

I'll call Isuzu tomorrow to check the prices on the hose connection ports, O-rings, and heater core. Depending on how ludicrous the price is, I might actually test this stuff and try to make damn sure the leak is something I can't fix myself.
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Old 11-24-2008, 08:58 AM   #12 (permalink)
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WOW thats one hell of a write up. Congrats on getting that far. Don't cut corners, you will end up doing it again....be there done that...get your parts ( shop for best prices ) then put back together.
side note, you'll only be able to see the leak if under pressure, it is probly the core, my rodeo did the same thing.
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Old 11-24-2008, 06:05 PM   #13 (permalink)
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Apparently, the O-rings and 90 ports and heater core are sold as one unit from the dealer. $357.39 including shipping.

I'm going to try new O-rings, reconnect the ports, and then rig up a way to pressure test the heater core to make absolutely sure the leak is something/somewhere I can't fix, before I lay down $357.

I wish I still had my '65 F-100. I could just plumb it in series with the heater that's in it.
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Old 11-24-2008, 06:19 PM   #14 (permalink)
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ya 2x on the 65 F-100 that was when cars were made easy...yes go napa take your old ring in and match them up, I did the same.
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Old 11-28-2008, 08:12 PM   #15 (permalink)
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OK, so I got two O-rings from the local NAPA to replace the O-rings that I thought were questionable, and rigged up a pressure tester as follows.

One 5/8" rubber crutch tip widdled down slightly with a box knife is fastened to one of the hose ports on the heater core with a suitable hose clamp to block it off.

On the other heater core port, a 12" piece of 5/8" ID clear vinyl hose is fastened with a similar hose clamp. At the other end of this hose is a 5/8" hose barb to 1/2" Male NPT adapter, fastened with another hose clamp.

The hose to NPT adapter is screwed into a 1/2" NPT Tee fitting.

In another port of the Tee fitting is a schrader valve to 3/8" Male NPT adapter along with a 3/8" female to 1/2 Male NPT adapter bushing.

Finally, in the third port of the Tee is a 0 - 30 PSI acetylene pressure gauge (1/4" NPT male adapted to the Tee with 1/4" female to 1/2" male bushing).

I got the idea for this rig from a job I worked last summer at a small engine repair shop. The guy that ran that shop had a similar thing rigged up, but the hose barb was much smaller, and instead of a schrader valve, he had a pumper bulb like what's used on a blood pressure test cuff. He mostly used his to test for bad fuel lines on chain saws.

The acetylene gauge works nice for this, because it goes 0-15 psi in half of its scale, so there's pretty good resolution, which better lets you see the smallest of leaks.

Total cost of the pressure testing parts was just just under $30.

As far as I can tell, the stock pressure for the trooper radiator cap is 16 psi, so no need to test far beyond that.

I knew I wasn't going to have the convenience of a pumper bulb any time soon, but felt I was lucky as heck to find the schrader valve adapter. I was really sweating how I was going to carefully and accurately pump this thing up.

I pumped it up with my bicycle pump and it bled down to zero in a few hours. So, I pumped it up again and checked all my plumbing connections with 409. Sure enough, I found a few that needed tightening. It almost goes without saying, don't forget the Teflon tape.

With all that out of the way, I'm pleased to report that my old heater core with new O-rings has held 15 psi for several hours now.

So, tomorrow AM, if I see that it has held pressure all night, I'm going to crank up the extremeness of the test a little.

I'm going to take the crutch tip off one port of the heater core, and fill it up with a strong solution of food dye and water, put it back together and re pressurize it maybe to 9 or 10 psi. Then I'll dunk the heater core in a 40 quart stock pot of hot water. I'll slowly run the temperature up to 200 F while making sure the pressure in the heater core doesn't get too high. Once the pot is up to 200 for a while, I'll bump the pressure of the heater core up to a wee bit over 15 psi. I'll try to keep that pot at an even 200 for a couple of hours and see if the water leaks out of the heater core. If the water does leak out, I'll know when the gauge goes down. And, if it does leak, I hope the strong food dye solution leaking out into the pot of water, will let me see where the leak is.

Anyway, wish me luck, but I'm starting to think the heater core leak was indeed the O-ring joints, and all it needed was new O-rings.

More later.
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Old 11-30-2008, 02:01 PM   #16 (permalink)
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OK, so no food dye was handy, but I really only needed that in case there actually was a leak. So, I cooked 'er up nice and hot anyway, and it held pressure for a few hours while I held the temp of the pot around 200.

I'm going to go ahead and install the old heater and start piecing this thing back together.
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Old 12-01-2008, 01:22 PM   #17 (permalink)
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congrats man good luck on the put back together.
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