Hey guys as the title says I'm having issues with my heat. Here's whats going on, If I turn the vent selector to ANY position AND if the fan speed it on 1 or 2 Its blows fine (Not hot) just blows air. IF I turn the fan to 3 or 4 the air blows more then you hear a "pop" and NO air is coming out. ALSO THE AIR COMING OUT IS NOT HOT, if its on #1 fan speed it will get warm but never hot.

Upon first search on google and here I found numerous links, videos and post to the blend door. I pulled the glove box the other day and saw the diaphragm valve and with the key in the ON position I turned the vent selector **** and watched the arm move in and out as the blend door its self moved.

Removed the center dash and radio tore out some of the foam for the vent flap to the defrost. with the jeep running, defrost selected and fan at 1 its ok. started moving the fan speed up 2 ok....3 flap slams closed in a few seconds....turned selector off and back to defrost then #4 fan speed and immediately slams close.

I had gone to the bone yard a few weeks ago and found another HVAC panel, I also replaced this with the exception that the COLD/HEAT section from the 1 i pulled was for a cable and mine is electronic, I sawpped that section out.

So It seems I either have several Issues or just one issue with multi symptoms.....
The Radiator and water pump was replaced 3yrs ago and flushed out the system (probably should be done again).

Im kinda stuck on what is causing all this mess, Im going to pick up a vacuum pump and start testing all the diaphragms for the selection to see if its the whole vacuum. what else could cause the NOT GETTING HEAT part. Ive read a little on the blend door actuator motor.

Sorry if this is confusing, I'll try to explain it better if needed.

 

Try flushing core through both hoses, alternatly.
As to the rest, no clue.

Ya, been colder than a well drillers taillight eh? -10 tonight.
How's global warming going for you?

News flash, crime down 38% in DEEtroit.

 

i know -10 thats warm lately....

Ive got an old ford with a heater that"ll burn you outta your close, just want to get this fixed so i and drive it daily again.

 

Please add updates as you go....my 97 xj has what sounds like almost the same problem. When i got my xj almost 2 years ago when you would turn on heat or cold on any speed...1 2 3 or 4 air would flow then POP...nothing. didnt matter if you had it on defrost setting or split level or face level. The only thing that would work is feet level. It definitely works. Ac blows cold...heat is warm at best....and only on feet. Now here in the last few months i lost all speeds except 4....figured blend door was an issue. Beyond that i had no clue. Figured id tackle it when i replace the factory radio since i gotta take part of the dash apart any way but not having defrost really sucks. Any info you come across while working on yours may be a huge help when i finally tackle mine.

 

2 issues:
#1 Vacuum leak, Mode door is not being held in position.
#2 Blend door linkage broken, actuator operates externally when changing between cold - hot, but is no longer actually connected to the blend door.

 

Was just wondering, what do you guys think. If both lines from the engine into the firewall are nice and toasty hot, that would mean the heater core is not clogged, right? If it were clogged, at least one could be pretty cool, me thinks.

If it's warm but not hot, with the gauge up at temp, the heater core could be restricted. The smaller tubes there sort of work like a filter for crud in the system. It's not hard to back-flush, that doesn't always work though.

 

I have no idea why it won't blow at 3 or 4, but it does sound like your heater core might be struggling. Just an FYI, I flushed my heater core this fall and have great heat when it's not this damn cold. It seems like it takes a lot longer for the entire HVAC system to heat up in this cold, especially when you hop on the highway 5 minutes after your Jeep starts like I do every morning. So if the air has only been warm just since this cold started, that might be the issue. If not, I would flush your core. I did mine a little differently, following the way a buddy does his MJ, and improvising a little bit. I first blew the thing out with a compressor, switching directions until I was confident I got all the fluid out. Then I filled it with CLR and let it sit for a couple hours (some people may disagree with this, but the relatively soak time shouldn't do any damage). Then I flushed it out with a hose, again alternating directions until the water ran out fairly clear. Followed this up with another blast of the compressor just to be sure, and topped off the coolant reservoir. It's a really simple job, and not counting soak time, should take less than a half an hour.

Also, I'm in Ann Arbor. I feel your pain.

 

Correct.

 

#1-Do I need to test the main vacuum for the HVAC control or individual modes? I'm planning on picking up a vacuum pump with Guage tomorrow. Could it be possible that the check valve at the firewall is bad?

#2- is there a good tutorial or video on the blend door replacement? Seems like all the one I find are for the grand Cherokee or wrangler and the blend door is behind the glove box. With our Cherokee is under the dash so I'm not sure how to cut it out or what exactly to cut. I work in a machine shop so I plan on making a new door out of either sheet metal or aluminum.

Thanks for all the info so far.

 

It does blow on 3 and 4 but I'm loosing vacuum and the flaps close so no air comes out. You can hear it moving air but it's not coming out where it should be.

 

This help?

 

Thanks but no I have that and the color coded one for the selection **** on the HVAC panel. I jump unsure if I need to test the main or all of the individual lines for the vent selection.

 

So I've bought a vacuum pump,but haven't had a chance to start testing. Does the 99's also have the same issue with the vacuum can behind the bummer or the hard plastic hoses cracking?

 

Yes.

 

I had same issue with my truck
I recently had heat and then didnt
I had to replace the actuator that controls the blend door
All good