brandon402

Ok, so I replaced the t-stat and replaced the temp switch today. My temp readings are now much more stable and accurate. No clue if it was the t-stat or the switch or a combo of the two. Either way, im getting accurate readings now. However, Im still not getting the heat I should be getting. Its just kind of a lukewarm kinda air.

Im not 100% I burped it completely, so I plan on doing that tomorrow. I opted for the method of burping where you crack open the temp switch and let the coolant come out until it stops bubbling and just flows.

If this doesnt solve the issue, anyone have any ideas?

Stan6406

Keep in mind if its extremly cold your heat isnt going to work as well
I've been in few places I had to get cardboard and cover part of the radiator to cut off the air flow

brandon402

Yea, I considered that as well. I have my entire rad covered with cardboard (I believe we saw -25 today, so I figured it was a good idea). My roommate and i are now looking into flow diagrams for the system. Starting to wonder if that bypass valve is inline with the wrong one of the 2 core connections.

Stan6406

Just putting this out there not sure if it would be a good idea or not
Can the heater control valve be bypassed? Here in ohio the heat pretty much stays on max until spring?

brandon402

Good idea, however I have already t-shot the valve and, from what I can tell, it is working properly. When the temperature portion of the controls (the slider that goes all the way blue to the left for cold and all the way red for hot to the righ) is moved all the way to the left, that valve does close and I do see a complete loss of heat. And, then conversely, when moved all the way right, I begin to get my lukewarm heat again.

I really need some help here guys. With the wind chill, its been -25 for a couple days here. I had to put a blanket in the back for my son to make sure he stayed warm this morning. My next step is to do a complete reburp of the system tomorrow, but after that... Im at a complete and utter loss. I plan on enclosing some pictures as well, to give people a good look at what Ive got going on.

By the way, are there DETAILED instructions for the burp? As I said earlier, I plan on using the temp switch as my burp point, cracking it open and watching until the coolant flows steadily out of the hole. Is that the correct procedure? Just double checking.

chrisl757

I think we have the exact same problem Brandon.

If you are getting HOT heat on DEFROST, then there is no need to do a burp, because your coolant flow is already good. The only thing that putting the temp control lever to DEFROST does is that it changes the door configuration for the blower fan.

Sooooo, I think we both have a vacuum/door issue. My understanding is that for the systems in 96 and earlier, they don't use a blender valve to regulate the coolant temps through the core--the 96 and earlier use a "blend door" to mechanically regulate how much external cold air is mixed with hot air from the heater core.

I think our problem though is in the door you looked for. I can't find it, but if you pushed the arm of the door all the way and the system got HOT, then that is the problem. It is not getting enough vacuum likely.

I have since learned about the vacuum canister and vacuum lines in the system (which all have to be connected and not cracked) that control how much vacuum you have to seal that door one way or the other. Bottom line, if you have a bad vacuum line connection or not enough vacuum, the doors won't close all the way, and then you get what we get: luke warm air.

I think this is because the door doesn't shut completely to the outside air, and so it is letting in the frigid air and that is majorly cooling down the heater core air.

We have to figure out how to get that door to stay shut, and then we'll be toasty.

Now, where is that little arm of the door that you're talking about? I think that is the problem.

yorkite

Hey, I've been following this thread, and have to say I'm in the same boat. Mine's an '87, and have gone through all the steps you have trying to troubleshoot too.

I have done:
New t-stat (195)
flushed the heater core
replaced the heater controls
checked the heater valve
put in a thermostat housing from a '92 to burp the system easier (see picture) - seems like that worked....but not 100% on whether there's still trapped air or not.
I've been seeing alot of people blaming the thermostat on different threads - I find it hard to believe that both of us have brand new faulty thermostats.

p.s. - I'm also freezing my ***** off in omaha too. I gave up, and have been watching the forums for a solution.....let me know if you find anything out.

chrisl757

Brandon,
I think the door you are talking about that is under the passenger side of the dash is your RECIRC door. that door is only open on MAX AC so that it can recirc the interior cabin air to get it even colder in the hot summertime.

So that door is not the problem.

I attached a diagram of my HVAC system with the vacuum lines (96). I don't know if that is the same for you....but if so let me know.

Here is what I have figured out so far:
There are 5 doors in this system:
Recirc door
Panel door
Floor door
Defrost door
Blend door

Here is what I have determined:

Recirc Door works. If I go to MAX AC, it opens like the diagram says. You can see it working.
Panel Door works. If I go to VENT controls, I can feel the air blowing through the dash panel vents (although it's not hot).
Floor Door works. If I go to HEAT controls, I can feel the air blowing through the floor (although it's not hot).
Defrost Door works. If I go to DEFROST controls, I can feel the air blowing on the windshield (and it is hot)!
Blend door????? I think that the Blend door is controlled by the red/blue temp control slider lever on the dash. I think I can see the actuator through a cable that is under the passenger dash. I don't think the blend door is vacuum controlled in mine because I can watch the cable move as I slide from hot to cold and vice versa.

When I move the blend door to the cold, it gets VERY cold. When I move it to hot, it's lukewarm.

I have heard that depending on how these are made, they can disintegrate, or a mouse could have chewed through it, or it may just not be seating well.

I'm still not sure why defrost would be hotter though.

Can anyone here describe what the blend door looks like? (I can see the external parts, but I want to know what it looks like internally.) Is it worth tearing the dash apart to check it out?

brandon402

Well, if theres 3 of us collectively trying to find an answer, maybe we can help each other out. I can see all 3 of us have done the exact same t-shooting steps. I have NOT replaced my controls, other than that, Ive done everything. So, having said that, what else is left?

I am leaning towards the blend door hypothesis, however... I checked (what I thought) was that door and it opened and closed in accordance with the various positions on the vent controls. Unless this isnt the door that I should be checking?

Again, I am going to post a pic of the following right after work today:
My engine bay
What I think is the blend door
My controls

If you guys can think of anything else you would like pics of, by all means ask. Together, we should be able to come up with something. I just wish I had a good FSM.

brandon402

AH! I am definitely NOT seeing the blend door then. I think I am seeing a panel door. The door moves by way of a diaphram that is visible. Is the blend door further behind the dash stuff?

chrisl757

so here are pics of what i think is my blend door.

the second pic is the recirc door (behind the cross pattern is the actual door)

If you look at the HVAC diagram you can see that when you push the lever to MAX AC, this door opens up to recirculate the air through the car and get the cold air colder.

now the blend door....I can hear it changing positions internally, but I don't know if it is a flimsy flappy material that has crumbled over 14 years of abuse.

and if you look at where it is located, it seems like a real challenge to get at this thing. I don't want to take apart the dash at all if I can help it.

brandon402

Hmm... interesting. Well, I have ALL weekend to tear into my dash, and ive done it somewhat before, so I'll just get into it again. As for that second pic, that little shield there, with the philips head screw... thats the other door that I was thinking was the blend door. Which its not.

Btw... yorkite... if you want to meet up sometime and try to t-shoot this stuff together, shoot me a pm. I'll give you my number and we can try and figure it out. I primarily do my t-shooting on base, cuz we have a heated auto hobby shop to work in.

Oh, and if anyone else wants to throw in there two cents about blend door locations, please by all means do so! Thanks!

brandon402

I had to do some digging, but I remember timber posting this picture up once in another thread...



I wonder if this is what we are looking for? And if so, where is that?

yorkite

Brandon, I think you said you had your cooling system serviced professionally right? I have a gut feeling that the cooling system is fine, as is mine, (as far as having to burp the system). I did all my cooling stuff about 1 1/2 months ago, and have continually checked it weekly to make sure all the air was out, including removing the temp sensor in the back of the block.

Chris is correct about the blend door being cable operated. I'm gonna take a pair of pliers tonight to the cable and see if I can pull it further to the heat side to check if it's closing all the way. Also will be checking the vacuum egg-canister behind the bumper to inspect the lines, as I think this is related to the heater controls.

I as well will be tearing into mine tonight to get this resolved... I kind of have to now, as my driver's power window quit working 1/4 of the way down as of noon. That's going to be a fun ride home.

Could the coolant mix be too rich to cause this? (not enough water vs. antifreeze?)

chrisl757

if your coolant is at 210 temps when hot, the antifreeze mixture isn't going to matter.

I'm not an expert, but the only point of antifreeze is to keep your coolant from freezing in cold weather. I'm sure it has some properties to minimize corrosion in the cooling system, but basically it's there to keep your block from freezing up in the cold. 50%, 70%, whatever, just keep enough in there to keep your block from freezing.

I monkeyed around with my heater hoses going into the core today and they were pretty stiff. so I started to play around with the heater valve and i pushed the rod arm up so that it would close the valve and then I cycled it a few times to see if I could sense a difference in the flow.

Then I decided to zip tie the arm to the diaphragm and go back in the jeep to see if the temperature cooled down. (In theory, if you close that valve, it should cut off flow to the core, and the blower air should start to get cold). The blower air got cold right away. So, my heater valve (and core) works to a certain degree. It's hard to tell if the valve could be clogged or not giving full flow through the core, but I think it is ok.

I will say though that I am going to flush the core one more time tomorrow, and here's why.

When I flushed it the first time, I was careful to put just enough pressure to get a good flow, but I didn't put the full water pressure from the garden hose into the system because I read that you can overpressurize your heater core, and then you'll have a huge mess in your cabin (along with having to replace the core). HOWEVER, I am starting to wonder now if I didn't give enough pressure to the system and maybe that is why I'm getting lukewarm air.

So tomorrow morning, I'm going to hook up that garden hose again and flush the core just one more time to see what it'll do. I'll open the garden hose valve a little each minute to build up some more pressure this time.

Will keep you posted.

Also I think the picture you're showing is the vent and defrost door configuration once you rip the dash apart.

I am REALLY avoiding going into the dash because I don't want to disturb anything and make things worse.