99XJ 4.0 WEIRD HEAT PROBLEM!!! HELP!

I went to school for automotive, and never seen any issues like the following.. No heat is one thing, but mixed temps between pass/driver when there isnt dual zone is messed up..

Ok here's the story... I bought this Jeep with 182K for 1500. The previous owner said that the A/C wasn't working thought it had a leak. I charged it and it seems to hold a charge fine and the system works well. The problem Im having is that it's quite cold now in chicago and the vents are doing some weird things. I want to note that I replaced the thermostat, flushed the heater core, checked the hoses, and the 99's DO NOT have the heater control valve.

The TEMP GAUGE on the dash does work and sits under 210 while driving, when the jeep sits its maybe 210-190 while the thermostat and fan are cycling. The cooling system seems fine.

The problem is as follows...

****When its cold out and I have it on panel vent the drivers side vents(2) are nice and warm while the passenger sides are almost cold.

****When the blend selector is on floor both drivers side and passengers side are both quite warm.

****When the blend selector is on defrost, both drivers side and passenger side of the defrost vent are warm.

I wouldn't say that the heat ever gets "knock your socks off" hot which I dont like. Every car I've owned(12 cars) in my 12 years of driving have always had super hot heat.

Any ideas would be great.. I've been looking for a diagram of how the heater box air flows through but havent been able to find one..

Check your vacuum lines for the odd venting issue. My '99 just recently started having the dash vents cut out when really hot. To get it back, I have to switch it to the floor vents and then back to the dash vents. It's just too cold here to mess with vac. lines right now.

As far as not getting hot enough, when's the last time you replaced the thermostat or flushed the cooling system? My heat gets so hot that my wife and kids complain about it, and I have no carpet or headliner and all the factory drain plugs have been removed (open holes).

As I stated.. The problem isn't it getting hot enough.

I disconnected the vac connection and they seem to be doing their jobs as well.

Thanks for the idea

anyone else with ideas?

I had no heat initially, but after doing the full flush including the heater core and changing the water pump, thermostat and gasket (from jeep). I have great heat from the drivers side (2 vents). Ive realised now though that i have the same problem as you. The passenger vents blow barely luke warm and dont get any hotter no matter how long i leave it. I very rarley have passengers in the car so its not a major issue, but would like to know how to fix this for when the wife does join me for a drive. Ideas Anyone?

I tested my 2000 yesterday, and the heat is good from both pass and driver side vents. Vehcile does heat up plenty good that you have to turn the heat down, even at 10 degrees outside. I've had a lot of different HVAC apart doing warranty work and I cant see what would cause your problem. But on automatic systems, the heat gets blown our on the floor, and the AC gets blown out of the vents anyway.

Do you have the dual zone heat? i think a duct fell off or a blend door maybe damaged. they have blend door issues with the grands and dual zone heat.

Take a look at this writeup.

I'm not endorsing the product, you can see from his pics what the original door looks like.

http://www.jeepsunlimited.com/forums/showthread.php?t=854246

Oops. Never mind, this is a ZJ. But I'll leave this in anyway.

There is a similar blend door kit for XJ's too on ebay that is often linked to on this forum. But this is not Mike99's problem as he gets good heat to the floor.

winterbeater said:

There is a similar blend door kit for XJ's too on ebay that is often linked to on this forum. But this is not Mike99's problem as he gets good heat to the floor.

Click to expand...

Hence the "Never Mind" at the end.

Well, the heat's now luke warm again not hot like it was the other night. Although it could be due to the temps being -1*F here. Still the mix hot and cold situation with the vents. Its not a dropped duct since the vents are still blowing air through, it just is a temp problem. It gets to operating temp, I flushed the Hcore, and its got a new 195 tstat. I dont know where to go with this.. Im going to check out the rod above the blend door motor but im not holding my breathe..

So now your heat is gone again from the passenger side it appears that we have the EXCACT same problem with my 97.
When my cooling system was clogged it gave good heat both sides. Everything worked as it should. Now after full flushing/backflushing new jeep thermostat waterpump etc its all good apart from this mixed heat which kinda has a mind of its own. The difference in heat between the drivers 2 face vents and the passenger 2 vents is always there. Sometimes its only just noticeable, but the majority of the time its night and day difference.
The circular dials all feel positive. When switching to face vents to floor vents there is a slight delay of perhaps 3 seconds before the air changes direction which i understand is common. My vacuum lines all appear to work.
Ive had one t-piece fitted on EACH heater hose.
I havent got access to my jeep at the moment but what i will try tomorrow is closing both vents on the drivers side and see if it diverts heat to the passenger side?
Also, if i were splitting hairs, i would suggest that out of the two drivers side face vents, the vent nearest the drivers door is the hottest, but i would suggest this is always VERY marginal, but may assist with clues. The passenger side vents never blow out cold, just never hot?
I get good heat in the cab from the drivers vents and have to turn it down eventually, but its just very annoying

The heat sucks right now, never would have to turn it down.. The passengers always blows cold when on vent.. its not that no air's coming out, it just freakin cold.. ughhh

Did you close off the driver side and center vents and see if there's any difference on the pass side?

Hi,

I shut of ALL vents (but the far drivers side and the far passenger side vents cannot be closed completley.) This was allowing out heat on the drivers side only.

The passenger side was still blowing out at best luke warm heat.

Ive also established that when i have it on maximum power (number 4 settting), the problem is exaggerated. Decent(ish) heat on the drivers side, pretty much no heat from the passenger side.

However when i have it on a low power setting like number one on the dial, the difference in heat is pretty much negligable, with proper decent heat from the drivers side so i have to turn it down (all be it eventually), and better heat from the passenger side although you can still feel the difference!!??
The upper most heater hose is very hot, squeeze it for like 2 or 3 seconds at most. and the lower hose is cooler but still very hot, squeeze it for maybe 8 or 9 seconds before you get burnt.

closing the vents one at a time does increase the power of flow to other vents but the heat is not transferred??
how about that one then??

I did come to a conclusion.. well though it'd be a good idea to still do the flush and Tstat, a jeep guru in my neck of the woods confirmed that most likely it's the heater core. He explained that they are not like you're average GM or Ford heater core, they actually have very small tubes inside the core that very easily get plugged up. The way we checked this was getting the car up to operating temp and then feeling the hoses going to the heater core. One of mine was hot while the other was luke warm, which meant that the heat's getting blocked at the heater core and cant pass through. when you keep the engine at about 1500 you'll notice the hoses come to more of an equal in temperature. If this is you're situation, have fun taking the dash out and doing a heater core. I've since wired my recirc. door shut and its better than it was for the rest of the winter. I plan to tear into that the first 70 degree day we get.

I wanted to add that even though the heater core's small tubes will get clogged there's still bypass where the coolant can go around, but this wont allow much heat to actually get pulled off the heater core for the heating system of the heep. So a flush might seem like the heater core is in good standing such in my case. Well I was wrong.

Hi,
Sorry i sent you a few pm's but when i didnt get a reply from the last two i thought you had got it sorted.
i fixed my problem by burping the system. (god knows how that could fix this but it did).

I could have swore down that my system was full because there was zero tell tales signs of air in the system.(i also thought that you couldnt get an air lock in an open system).

I can only assume that an air pocket was trapped in the heater core, yet coolant was still circulating around the "channels" that your talking about. And instead of mine being "clogged up", there was simply no coolant getting to all the right places within the heater core.

Maybe im wrong but increasing the revs leading to an increase in tempreture of the hoses is also a sign of air in the system??

Also if you recall, there were three of us having this problem at the same time. The other guy got his sorted i believe from burping his system. I dont know if this will work for you. I dont know if youve tried it already but if you havent, it must be worth a try even if you THINK that its full.

I appreciate that your jeep guru may have suggested heater core replacement, and he's probably right as hes the expert whos seen your car, but after i spent hundreds of hours looking into this subject on various posts from various sites, I shudder to think how many heater cores were replaced needlessly (i was also advised heater core replacement)!!

good luck and let us know how you get on

im going to jump on this band wagon and be part of the weird heating issue as well. My 98XJ has the same problem with the pass side vents not putting out near the heat the driver side. I have flushed the heater core a couple times, it has a good t-stat and heats up great but just blows cooler on the pass side. Doesn't make any sense at all.

well I sorta have this problem.

I replaced water pumper, rad, and thermo and ever since then I get a barely luke warm heat system.

I'm starting to think my heater core is clogged because I had a ton of junk in my old radiator