brandon402

Ok, so I just got home from doing a quick dig into the dash after work today. I verified that those diaphragms depicted above are indeed the actuators for the defrost and heat. And they both appear to be working. Either way, thats not our issue anyway.

I also dug into the dash as much as I could in hopes of finding that blend door. Which, I did not. However, I did get verification from Timber on here that you cannot get to the door without pulling your dash. I asked him for a write up so hopefully I can get one and get into the dash soon.

chrisl757

I didn't get a real good visual inspection of the vacuum canister, but I did pull the little top off of the vacuum line right by the battery to see if there was suction while the engine is running. There is a little T in the vacuum line on the passenger side that runs along the edge of the passenger wall. That T has a strange looking black rubber wedge cap. I pulled it off...hear solid sucking noise....so I have good vacuum. I didn't think that there would be a need to check the canister then.

I'm pretty sure we all don't have a vacuum problem because the vacuum controls the doors. If you have air blowing on the floor in HEAT, to the dash vents in VENT, and to the windshield in DEFROST, then you've got good vacuum. That leads me back to the blend door (which is controlled by the cable and NOT by vacuum).

OR....as I am now starting to wonder....did I flush that core well enough?

Please somebody if you're reading this stuff, jump in here and give us any ideas.

1jeepman

Does sound like the heater core is restricted.

yorkite

I'm going to throw another thought out here.
I had NONE of these problems till I got a leaky radiator hose one day, and replaced all of the cooling hoses. Pretty sure that they were all factory hoses still. I know they are hooked up correctly now, and before all of that took place, my temp gauge always sat at 210. Now I'm at 190-200 consistently.

chrisl757

hmmmmm.

yorkite, did you replace the thermostat? They could have given you one of those 195 thermostats (different from the 220 stat).

Even so, that shouldn't make too much of a difference such that your heat is luke warm.

If you did get a 195 thermostat from the parts guy, you could replace it to the 220 one. not sure it'd be worth the effort though.

If all of us have a blocked core that needs flushing, you could have inadvertently blocked your core when you put new hoses on....There may have been some crud somewhere in the system that started to flow freely through your new hoses.....and then it settled in your core??

Hard to tell for sure without flushing the heater core again.

4.3L XJ

Pretty cold there in Nebraska right now? When fresh air comes in through the HVAC system if it is say 20 degrees outside it needs to be heated to around 130 degrees to feel good and hot. That is a 110 degree jump. That is real good for any heater. There is a good trick to use in cold weather in winter. If you have AC, just pull the relay or pull the plug on the low pressure safety switch. Then put it in MAX AC. The compressor won't come on and you can use it as a heater. It will then recirculate the cabin air and feel much warmer.

smtippin

Where can I pull the relay or the plug on the low pressure safety switch on a 96?

Thanks,
s

yorkite

Well, it had a 195 in it to begin with also. After the cooling system was put back together, refilled, burped, I didn't really use the heat too much to notice this heat problem till a week or two later when temps dropped. That's when I noticed it and took both heater core hoses off and flushed it (with full-blast hose pressure). I did that about 10 times each way and it was clear.
I think tomorrow's day will be wasted pulling the dash apart and trying to inspect the blend door and the heater core.

Also here's this: http://www.naxja.org/forum/showthread.php?t=931690 on how to replace heater core, if you're considering taking the plunge like I am. This procedure might reveal the magic blend door too.

chrisl757

4.3L XJ is right. The MAX AC trick worked for me. By putting the system in MAX AC and making sure the compressor was off, I had recirculated air, (since the MAX AC is the only climate control setting that opens the recirc door). The heat wasn't super hot, but it was much warmer, and it kept getting hotter.

That is starting to lead me to believe that this is truly a heater core issue. There's no way this could be a vacuum issue for me because all the vacuum doors work. The blend door (which is cable operated) worked well enough on the MAX AC setting to get the air warmer.

I think I need to flush my core both ways with more pressure and see what happens. I might also need to get a prestone flush cleaner and run it through the system to see if that would help.

Yorkite, I wouldn't go tear into the dash at all this morning until you check or replace your thermostat. Your engine temps at that T-stat housing need to get up to 210, and if you are only hitting 190, that is going to make a difference. I might have made this confusing by calling it a 195 thermostat--Actually that is the one that you want. OEM is 192 or 195, but your temp gauge on the instrument cluster inside should read about 210 once the jeep is warmed up. There are a whole range of thermostats out there that run cooler and your parts guy could have given you one of those. The theory behind those is that is prevents overheating in the summer. Obviously that is not an issue now though and you want to get that cooling system to run at 210, so if you could do that by just changing the thermostat, that would save the effort of going into the dash.

These heater cores are really just heat exchangers, and Newton's law of cooling says that the rate of temperature change (which we're looking to BOOST up now) is dependent on the difference between temperatures. Soooo, get that cooling system up to 210 and more than likely that will produce SOME sort of increase in heat. From what it sounds like, it could be a 20 degree additional temp differential for you. That doesn't mean your air will get 20 degrees hotter--but it might get 10.....

One other thing to note to all, the way this heater core works is that the more blower speed you have, the "cooler" the heat is going to get. That is because even when the system is running perfectly, if you are blowing cool air faster over a hot heater core, that air is spending less time getting warmed up by that core, so it is not going to be as hot as when you have the fan on LO. That is not to say that the air shouldn't be hot....just that it won't be as hot as the LO fan setting.

Happy hunting to all today.

VARG7

I feel like i have the same problum on my 90 cherokee. i had no heat at all then i replaced a couple hoses on it blew some pressured air through the heater core it seemed pretty clogged got it back together and now i got a lil heat jus not hot at all. next im gonna tru bypassing the little control valve thats in the line that might not be opening all the way so there for the coolent will go th the overflow bottle instead on the heater core so u bypass that valve and itll all go to the heter core instead?? sounds good lets see how it works lol

smtippin

I haven't read through all of the techy posts to see if this was brought up, I imagine it has been, but for the purpose of redundancy, I recall a time when I was installing my stereo and unplugged some cables that hooked up the dial below. I cannot recall all of the symptoms, but if you're going to be tearing your dash apart, you may want to see if there are cables unplugged right below your stereo.

s

goobs_63

hey there ! im having the same trouble with my 89 4.0 auto i also have done all the flushing and whatnot but still only warm air. I think the blend door might just be the culprit and i think all of these xj's have vacuum trouble. Fortunately for me freezing up here in nd i could be wrong but if the recirc door is opened up while running should cold air be blowing out of it? I had it in the garage running yeah smart i know but with wind chills to -50 whats a little carbon monoxide i opened up the door and it was very cold air coming our of the recirc door. I am interested of this blend door could it be accessible if i were to say remove the glove box or sawzall the passenger side of my dash off this is my first jeep and it is being a little annoying but i love it

chrisl757

a couple things:

first of all, the blend door is not vacuum controlled. All the other doors are vacuum controlled. If your blowers goes to windshield on DEFROST, goes to dash panel vents on VENT, and goes to floor on HEAT, you basically don't have a vacuum problem.

The recirc door does one thing only. It seals off the outside air opening so that the blower fan takes a suction on the air in the cabin below the passenger dash. Sooo, if you push the RECIRC door partially open with your hand, you will feel some cold air because you're opening up to the external air. If you open the Recirc door all the way, you will shut off the opening to the outside air, and then things will get hot. Although if you try to manually open the recirc door when the climate control is set to HEAT....the air blowing into the floor will get sucked right back into the recirc and won't make it to the rear (or really even the seats). What the MAX AC vent control does is take a suction on the air in the floor and pumps it to the dash vents. That creates a sort of conduction process to exchange the air temps to colder in the summer for AC.

Either way though, the RECIRC door has nothing to do with the heat really. It is only supposed to be operated on MAX AC. The trick cited above is a great way to overcome severe cold, but the Jeep was never initially designed for that.

You might want to take a look at cycling the heater valve several times by sliding the temp from blue to red (cold to hot) while the engine is running hot. I found that working that little valve some might have improved my flow a little because the HEAT got a little warmer. You could also cycle it by taking your hand and pushing the rod actuator on the valve itself.

So to recap, if your other doors are venting to the right spot, you don't have a vacuum problem.

it could be the blend door, but that is behind the center dash, so a sawzall on the passenger side won't get you there.

Sure would be nice if somebody had a picture of this blend door though. I am just wondering if it is something flimsy....

Abovetimberline

This is the blend door,it is the same as the others,the problem is they can fall off and the cable will slip. This is a spare I had from another xj and the cover is broke.

radio flyer

When mine was still all 85 i went thru all of the same things that several of you are doing to try to avoid replacing the heater core. I could feel heat on both lines at the core, so i thought that it could not be the problem!!! Wrong--Those of you with older xjs would benefit from a new core, if for no other reason than you may be avoiding the mess and nightmare of a blown heater core.