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AC Vent/temp issues

PopLockLSwap

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So I've got a 2001 Cherokee. Been slowly fixing things as they come up and now I've encountered an issue that has me stumped. I can turn the HVAC controls to all the different positions and the air will be directed towards them no problem HOWEVER it doesn't matter if it's dash vent, or floor vent air will also always be diverted to the defrosters as well. Like I'm getting air from the dash vents when set to dash only, but I will also get air flowing through the defrosters with it. I don't know if it's suppose to be that way or not but I can't imagine that's the case. I've checked the vacuum lines coming from the Intake Manifold, traced them back to the vacuum lines on the side of the fender on the passenger side and to the reservoir that's behind the bumper. I've replaced one line because it was suspect and I replaced a hard line because it had a crack in it. My cruise control works just fine as well. I need to find some 90 degree elbows or something for the Manifold to HVAC vacuum line because that's super loose and just doesn't feel tight.

Anyone else encountered an issue like this? I didn't comb over every inch of the hardline because it holds vacuum.

I've attached a handheld vacuum pump to the vacuum line that connects to the manifold and it holds vacuum and when the engine is on, it'll still hold some vacuum as I change the settings on the interior HVAC controls.
I've ordered a replacement valve that connects to the intake manifold that's for the HVAC control vacuum lines. It's the one way valve but I can blow air in either direction however I do not believe that to be the overall cause of the defrosters getting air as well as every other setting.

My second issue is the AC in the jeep doesn't seem that cold? It's not an Ice box which I get, but it also doesn't seem that cold but more COOL for max AC windows up. I've had the AC system serviced recently. As a side note, the heater also doesn't blow HOT just warm. I don't think the heater core is the issue as both hoses going to and from it are hot when at operating temp. This leads me to believe it's possibly the blend door that's the issue. I can observe the actuator motor moving the door when changing from HOT to COLD so that's working as it should, but I've also read up that the blend doors are a cheap and flexible plastic that over time are just trash. HeaterTreater is a solution I'm looking at and wanted to try and get some other opinions before I spend the money to fix this door issue.
 
I would agree that the blend door is suspect in issue #2. If you can remove the actuator, you may be able to manually rotate the blend door to see if the shaft broke. While off, you can see if the actuator rotates the full distance.

Issue #1 is a bit trickier. The only position that should have defrost and another vent is the "mix" setting (the one above defrost only). This should send air out the defrost and floor vents. The defrost vent defaults to open when no vacuum is present. There are also 2 lines off the back of the HVAC control that set the position of the defrost vent door. One that closes the defrost door fully, and one partially (for the mix setting).

It's possible you may still have a small vacuum leak as the defrost door needs full vacuum to close. Vacuum demand is highest on AC Bilevel (only recirc door vented) and AC Recirc (only floor door vented). I might try using the hand pump to create the vacuum instead of the engine. Set the selector to any setting other than "mix" and pump it up and see if it holds. Then try another setting. It's also possible there something interfering with the defrost door or actuator..
 
I would agree that the blend door is suspect in issue #2. If you can remove the actuator, you may be able to manually rotate the blend door to see if the shaft broke. While off, you can see if the actuator rotates the full distance.

Issue #1 is a bit trickier. The only position that should have defrost and another vent is the "mix" setting (the one above defrost only). This should send air out the defrost and floor vents. The defrost vent defaults to open when no vacuum is present. There are also 2 lines off the back of the HVAC control that set the position of the defrost vent door. One that closes the defrost door fully, and one partially (for the mix setting).

It's possible you may still have a small vacuum leak as the defrost door needs full vacuum to close. Vacuum demand is highest on AC Bilevel (only recirc door vented) and AC Recirc (only floor door vented). I might try using the hand pump to create the vacuum instead of the engine. Set the selector to any setting other than "mix" and pump it up and see if it holds. Then try another setting. It's also possible there something interfering with the defrost door or actuator..
I agree I believe the blend door is suspect just from how it's acting.

For issue #1 I'll pull a vacuum on the line coming from the manifold thats for the HVAC system and see what it does as I change selection modes. Should the engine be off when I do this would that matter?
 
I'd keep the engine off so you can maybe hear any hissing and door movement. Once you move the door selector, you should hear the doors move about as vacuum bleeds off.

And, I replied in the forum about the "invisible text" issue.
 
I'd keep th

e engine off so you can maybe hear any hissing and door movement. Once you move the door selector, you should hear the doors move about as vacuum bleeds off.

And, I replied in the forum about the "invisible text" issue.
So I saw a YouTube video about a broken linkage not being able to mechanically move the door right. Pull the front radio plate off and remove the radio and as I'm looking at the linkage watching it move I look at the flapper door itself and it's got two holes in it. They look like they're factory too which would explain the air coming out of the defrost vents at all times so now I'm wondering if someone before me did something OR if the holes ARE from factory and I just expected there to not be? Maybe I don't have a vacuum leak at all and everything IS working as intended aside from the blend door issue maybe.
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These are the holes I'm talking about. They look clean and not hacked. The door itself moves freely and locks all around with no other air escaping except from those holes.
 
There is some factory cross-connection as the ac runs during the defrost mode to dry the air.
 
There is some factory cross-connection as the ac runs during the defrost mode to dry the air.
I understand having the AC run for that but I don't quite understand why the holes are there if I select dash vents I'd want just dash vent air, not dash vent and some being deflected to defrost. That kinda takes away from the blowing power of the dash vents?
 
So looking up more videos of people replacing heater cores has shown me that that door generally doesn't have holes in it. There's a pocket off to the side of it that allows air to also get through but that's more natural. I think what I'm going to do is use some speed tape to cover those holes and see what happens. The more I look into it the more I don't believe it's a vacuum issue but a mechanical one of some kind and this might be it.
 
Alright, went and blocked those holes with some speed tape and what do ya know, air no longer is coming out of the defrost vents when i have the floor or dash vents selected. Defrost itself and Mixed vent works as should and I feel now everything is working as intended. For the blend door AC not being cold but cool, heater being warm but not hot I held my finger over the shaft part of the actuator and moved the temp select. It moves freely but there is a noticeable click that is felt as it's changing from cold to hot. I think I'm going to go ahead and order the heater treater door replacement and see how that goes.
 
Alright. It's been a minute but I've finally been able to get that Heater Treater door installed and I also did a cooling system flush. I also happen to change the blower motor resistor as I was right there.

Heater door was an easy install. Instructions super simple, door was made of steel wrapped in thin foam to block off the passages it needed to when selected. Checked to make sure the actuator was moving the door left and right before I patched the hole in the box back up. No leaks from it.

So after doing all of that I noticed that the heater still wasn't hot. Warm at best. AC I feel had a bit of a difference? I feel at this point I'm really asking too much from an old system but idk. So far it's working and that's all I'm thankful for. As for the heater I did an entire coolant flush. Flushed the block, Radiator and the Heater Core. I feel as if that made the biggest difference in getting the heater to actually blow hot. Overall pretty happy with where it's all at and I feel now it's time to move onto the next list item for the Jeep. Thanks everyone!
 
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