97 and up blend door fix and information

Hi Guys,
I finally fixed the heater blend door in the 99 I've been working on! I'd like to thank the guys from Heater Treater first off, because they were gracious enough to send me the cutting template for the 97+ models. Without this for guidance, I wouldn't have attempted to cut into the heater box. Details and pictures below...

Long story short, I spent about 3 hours today cutting into the heater box, experimenting with fixes for what I observed to be the problem and then putting it all back together to get a working heating/cooling system again.


Summary of situation
Ok, so the hvac temperature was "kind of" working in this 99. It never got as hot as it should have, and sometimes the cold wasn't very cold either. After ruling out problems such as the thermostat and heater core, I knew this was probably the infamous blend door problem.

My motor was fine, but part of the blend door shaft was broken. I originally thought that since a section of the shaft was broken, that when it cycled on that side, it created a temporary weak point, then the door popped out of position. Ultimately, I don't think that was the issue at all. I believe that the MAIN problem was that the top shaft end of the
blend door was NOT fitting into the hole in the top of the heater box solidly. I tried to make a metal sleeve for the broken bottom shaft (old bus fuse tin made into a circle, then soldered and grinded/sanded down), but the clearance was not enough for it to fit back into the bottom shaft pivot point.

The HARDEST part of this whole job was putting the blend door back in the hole that you cut for access. You really need to get the bottom of the door in the bottom pivot point, then push the top in at an angle. It's really a nightmare procedure and my forearms are pretty tore up from wrestling with it multiple times.


Details I observed after cutting into the heater box and fix:
1. door seemed really tight. This seemed to be caused by the top and bottom flaps being taller than they needed to be. Within the heater box, the flaps were bent about 1/8 inch, that is they didn't clear the box, they were in there bent against the top and bottom. I realize this is to make a tight air seal, but I'm pretty sure it contributed to the problem in my case. I trimmed those as seen in the picture.

2. the MAIN problem with my door was that when it would be put to full cold, the actuator motor stressed, and then the top of the door would pop out of the pivot point EVERY time! I sanded the top part of the top shaft end down, and I honestly believe that this was the miracle cure. I really don't think the shaft was sitting tightly in the
hole at the top of the heater box before....it was just kind of wedged against the top and that's why the air was not going full hot or cold, but was still changing. It was working, but was not sealing completely off one way or the other.

To seal everything up, I used this black locktite tape called "sumo" that I found at walmart. It is a LOT more adhesive that duct tape, and seems very durable. Time will tell. If it doesn't hold up though I'll prob use that aluminum tape next time.

In my case, the problem is solved for now. If it fails in the future, I'll be buying the heater treater door, but I really couldn't afford the $120 right now, again, I really want to Thank the guys at heater treater for being nice enough to offer the template. Any questions just ask or pm. Thanks

did this today works like a champ great writeup

bookmarked.

This is going on my "To Do" list.

I've got the same problem on my '98 XJ. The AC is not cold. The heater is not hot.
In addition, the flap that controls the defrost flow seems to be free to flop back and forth
depending on the fan speed setting.

In comparison, the AC in my '93 XJ can be freezing, and the heater can get hot as blazes
and the defrost works A-OK.

Thanks for the write up!

All the info here was really helpful. Thanks bunches.

I had a low heat issue in my 2000 classic.
Was hoping the blend door was not the culprit.

In the future if anyone ever 'thinks' it's the blend door, my brother called me and gave me some good info that saved me a lot of time and damage to my duct box.

Take out the glove box and you'll see the end of the area where the AC coil is, just left of center.
There is a slight 'step' back where the coil stops on the left hand side.

A bundle of wires are attached with a plastic push pin like used on auto trim.

If you take that bundle of wires out you can use that hole as a guide point to make a 1" or so hole to put your finger in and feel around from left to right and from top to bottom on the back side of this plastic duct housing.
Be careful anyway. I used a occilating saw, the vibrating kind?
I had to get it back from my squeeze though. Can't keep her hands off it.

You should feel nothing behind this plastic side.

Cut a 2x2 inch hole with the original push pin hole being your guide for the center of this hole. I'd recommend making this 2" layout before you do any cutting so that you know for certain where the hole was in the first place. You can make it bigger from top to bottom but from side to side, 2" is about it, maybe 3" if you were really patient.

Put your flash light close to the hole and operate the blend door.
It's so easy to see if it works or not, it's ridiculous.
Mine works fine.

My brother believes that the loss of heat is a clogged heater core so I'm going to flush out the entire coolant system in the next few days when this 'crap' weather leaves Fort Worth Texas.

Just a little bit of info passed to others that may prevent a lot of extra work for nothing, in the event the blend doors were not the problem after all.

In addition, if it were a bad blend door, I was going to pull it, replace it and put a manual lever on the bottom of the duct to open/close/blend the air. Much simpler and fail safe.

I really don't care if someone were to ask WTF was I doing reaching under the dash.

When it's cold, I only use heat.
When it's hot, I only use AC.

CYa
thanks bunches from you all.
Doc