Blowing cold air, not thermo. ??

[RaVEWHQ]

Okay, the heater portion of the HVAC has never worked since ive had the 96 XJ (busted core? dunno). Never really concerned me because the "vent" setting and "bilevel" setting did just fine. Defrosters have always worked perfect too. Nice strong hot breeze blowing through. I take a 6 hour drive, get back, and notice a day or so later I only have cold air blowing out my vents, not hot. I thought it was the thermostat. Picked up a new OEM one. The top rad hose gets REAL hot, overflow bottle has never been an issue or the rad fluid level in the radiator, and the fans kick on when the jeep get warm under the hood.

I, stupidly, haven't picked up the correct oil and temp senders from when I did my gauge swap, but I havent had any performance issues with the Jeep.
I changed the thermo and I am still getting cold air being blown out the vents. What should I be looking at next? I don't really know the exact purpose of the fan clutch, but others have changed that out. But isn't that just if your fan isn't kicking on? Please help, it's still chilly sometimes at night!

 

[Yucca-Man]

Clarify something for me please. When you slide the temp control all the way over to the right (hot), you DO have hot air blowing in all positions except "Heat"? Heat rarely works for me either, since it only blows through the floor vents, and on a cold day the draft from the glass rapidly overpowers it.

If you're getting heat from the rest of the vent positions, it's definitely not a problem with the heater core, thermostat, fan clutch, etc...it's a lack of oomph from the weak 'Heat' position.

 

[aardvark4x4]

Do you have a vacuum leak? some of the heater controls are vacuum operated. My '92 had no heat when I got it, and when I looked the vauum tank was missing from behind the bumper.

 

[RaVEWHQ]

Clarify something for me please. When you slide the temp control all the way over to the right (hot), you DO have hot air blowing in all positions except "Heat"? Heat rarely works for me either, since it only blows through the floor vents, and on a cold day the draft from the glass rapidly overpowers it.

If you're getting heat from the rest of the vent positions, it's definitely not a problem with the heater core, thermostat, fan clutch, etc...it's a lack of oomph from the weak 'Heat' position.

I -normally- have hot air blowing in all positions except "heat". I have just always used my "vent" and "bi-level" positions to heat myself. And for some reason, now it has stopped producing warm/hot air....just cold air (still strong tho!). I just don't understand if the upper radiator hose is still real hot to the touch and the overflow bottle is working properly...

I guess I could check the vacuum lines, but would a vacuum leak really affect the strength of the air, not neccessarily the temperature of it?

 

[Matthew Currie]

I -normally- have hot air blowing in all positions except "heat". I have just always used my "vent" and "bi-level" positions to heat myself. And for some reason, now it has stopped producing warm/hot air....just cold air (still strong tho!). I just don't understand if the upper radiator hose is still real hot to the touch and the overflow bottle is working properly...

I guess I could check the vacuum lines, but would a vacuum leak really affect the strength of the air, not neccessarily the temperature of it?

All the flaps in the system are vacuum controlled, so vacuum problems can affect the strength of the air. Make sure that the fresh air flap down at the lower right end of the heater is not hanging open. It should open when you turn the heat position to "off" but not otherwise. The coolant valve in the heater is also vacuum controlled; I think it defaults to "hot" when the vacuum dies, but it's worth a check too.

 

[hillbilly_jeeper]

Therse a vacume controled valve under the hood that shuts off coolent flow to the heater core when you turn on the a/c. although, it requires vacume to close it, i guess it is possible that it got stuck closed.

 

[RaVEWHQ]

Hmm, seems like the vacuum lines just affect if the air comes out or not (not the temperature) from what I am reading about. My only other thought is: could the head somehow be cracked??? But then again, wouldn't I notice that when I look at my oil dipstick or wouldn't the jeep run shitty? Ahh hell, this is getting frustrating!
I could understand if the upper hose was not that hot, but everything just seems fine. I can hear the flaps opening and closing just fine when I move the hvac controls around.

 

[xjoe]

Therse a vacume controled valve under the hood that shuts off coolent flow to the heater core when you turn on the a/c. although, it requires vacume to close it, i guess it is possible that it got stuck closed.

I had a no heat problem with the same valve, took it apart
and cleaned it has worked fine since.

 

[Yucca-Man]

Hmm, seems like the vacuum lines just affect if the air comes out or not (not the temperature) from what I am reading about.

Correct - vacuum only controls the doors/flappers. Here's a question for you; if you put the selector on 'Heat' with the temp control down as cool as it gets, does it blow air? I'm still thinking that the problem isn't there - I've had two Cherokees and noticed with both of them that you simply don't get warm using the 'Heat' setting. It blows heated air through the lower vents, but when it's cold out that's not going to be sufficient. I always use 'Vent' instead and that certainly seems to do the job.

 

[ih800]

Check the selecter valve on the heater hose may be vacuum controled, it may be dead in the off posistion.

 

[ih800]

Or May Be Vacuum Leak In The Heater Control System??

 

[ih800]

I -normally- have hot air blowing in all positions except "heat". I have just always used my "vent" and "bi-level" positions to heat myself. And for some reason, now it has stopped producing warm/hot air....just cold air (still strong tho!). I just don't understand if the upper radiator hose is still real hot to the touch and the overflow bottle is working properly...

I guess I could check the vacuum lines, but would a vacuum leak really affect the strength of the air, not neccessarily the temperature of it?

THE VACUUM LEAK WOULD AFFECT THE HEAT SELECTER VALVE (IF VACUUM CONTROLED), NOT THE FAN, VACUUM IS PRODUCED OFF THE INTAKE OF THE ENGINE NOT BY THE BLOWER FAN

 

[corbinafly]

You said that the upper rad hose is hot, but did you check the heater hose? Maybe the passage in the tstat housing that leads to the heater core is plugged. Or maybe your heater control valve is plugged or stuck in the cold position.

 

[RaVEWHQ]

You got it right on the nail! Check the lines going into the heater core (even tho my core is probably blocked since my "heat" setting doesn't blow any air) and there was a small bend in the lower hose. Replace the hose and gave it a little more length, and it works like a charm now. Thanks all!

Now if I can only get the right sensors for my temp and oil for my gauge swap, i'd be okay. Apparently the AutoZone computer isn't right when you pickup the sensor "without lights". Argh.

Thanx again!

 

[corbinafly]

(even tho my core is probably blocked since my "heat" setting doesn't blow any air)

Glad you found the problem.
Just because your heat setting doesn't blow any air doesn't mean that the core is blocked. If you get heat in any other setting (vent/defrost) then your core is fine. The heat setting only blows air down at your feet. If you're not getting any air in "heat" setting, there might be something wrong with the vacuum controls that move the flaps inside the air distribution thingy that directs where the air goes.

 

[Yucca-Man]

Just because your heat setting doesn't blow any air doesn't mean that the core is blocked. If you get heat in any other setting (vent/defrost) then your core is fine.

That's the point I've been trying to get across as well - I'd like to hear definitely whether there's heat from the other settings and so far I haven't heard it...

 

[RaVEWHQ]

vent, bilevel, and defrost are now (once I added the longer hose going into the core) are now blowing hot air. When sitting inside the vehicle and you slide the controls to these settings, you can hear the vacuum moving the "plates" on the inside of the ducts to make things happen.
I do understand now that my heater core -isn't- blocked, but I am just curious why I can hear vacuum moving things in other settings, but no air at all is coming out in the "heat" setting. Would these vacuum lines for the actual "heat" setting be under the hood, or eep! behind the dash near the core?

 

[corbinafly]

Are you sure your not getting any air in the heat setting? It's hard to tell unless you reach down and feel below the dash. The air comes from behind the center of the dash (kinda behind where the ash tray is) and blows down at the floor at your feet. If you take a look underneath that area, you should see where the air should come from.
It's kinda hard to tell when you're just sitting there. Even when the heat is on in my rig I can't actually feel the air blowing unless I put my foot or shin in the proper place or put my hand down there.
Hope this helps. If you still don't get any air then :rattle: I don't know.......

 

[Yucca-Man]

Are you sure your not getting any air in the heat setting? It's hard to tell unless you reach down and feel below the dash. The air comes from behind the center of the dash (kinda behind where the ash tray is) and blows down at the floor at your feet. If you take a look underneath that area, you should see where the air should come from.
It's kinda hard to tell when you're just sitting there. Even when the heat is on in my rig I can't actually feel the air blowing unless I put my foot or shin in the proper place or put my hand down there.
Hope this helps. If you still don't get any air then :rattle: I don't know.......

That's exactly my experience in two Cherokees. "Heat" doesn't do jack to actually keep me warm...even on High the fan doesn't blow enough air to offset the cold air coming in through the cracks and glass... "Vent" works fine for keeping me warm, down to -5*F (the coldest I've seen on the console thermostat)