JeepForum.com

JeepForum.com (https://www.jeepforum.com/forum/)
-   ZJ Grand Cherokee Forum (https://www.jeepforum.com/forum/f13/)
-   -   Heater stuck on defrost vents (https://www.jeepforum.com/forum/f13/heater-stuck-defrost-vents-4240338/)

BorderWalker 01-30-2018 01:24 PM

Heater stuck on defrost vents
 
As title says. My Hvac seems to be stuck on the defrost vents, even when changing the blower controls. Not sure if this is a one time thing or if it might prove persistent.

Manual controls, no ATC.

Anyone got an idea what could cause such as this to happen? Vacuum line issues? Something stuck somewhere?

I know I don't hear the "Hiss" sound I used to hear when I'd turn my blower off.

1996maroonzjf 01-30-2018 01:28 PM

Vacuum leak for sure.
The manual HVAC is controlled by vacuum and defrost is the default position if it loses vacuum.
My ZJ has a slight leak, it will blow out of the defrost in any position under high RPMs with cruise on. Cruise control is other main user of vacuum in ZJs. It operates in all positions under normal driving conditions around town, or with cruise off.

BorderWalker 01-30-2018 01:30 PM

Quote:

Originally Posted by 1996maroonzjf (Post 39618746)
Vacuum leak for sure.
The manual HVAC is controlled by vacuum and defrost is the default position if it loses vacuum.

Well, to be fair the last position I had it set to blow on was defrost + Floor vents. I'll check after work if it's also blowing out the Floor vents or not. Could only check defrost vents.

If it IS a Vac leak, is this self contained to just the HVAC system, or might I expect other systems to start having issues?

wingless 01-30-2018 01:36 PM

There are two damper doors that must be in specific positions for defrost-only operation.

One is the floor off / floor shared door shown on the left here.


https://farm5.staticflickr.com/4391/...65ba8540_z.jpg


The other is the dash vent / defroster vent door, with the motor / actuatuator shown on the left here.

https://farm5.staticflickr.com/4379/...d985e6b5_z.jpg

JonMopar 01-30-2018 05:34 PM

26 Attachment(s)
I had this problem last week. Vacuum leak at the "T" section in the vac line at the back of the firewall was the fix it my case. A line had popped out of the T

BorderWalker 01-31-2018 07:52 AM

...So I had a lightbulb moment this morning. Problem was still persisting last night and this morning, as well as Cruise refusing to work.

Then I remembered. When I was installing the Relay harness for my headlights on Sunday, There was a hose I unplugged which was attached to the battery tray.

That wouldn't happen to be a Vacuum hose related to the heater and cruise controls, would it...?

Cause if so, I may have had an idiot moment.

1shotleft 01-31-2018 08:01 AM

Quote:

Originally Posted by BorderWalker (Post 39622690)
...So I had a lightbulb moment this morning. Problem was still persisting last night and this morning, as well as Cruise refusing to work.

Then I remembered. When I was installing the Relay harness for my headlights on Sunday, There was a hose I unplugged which was attached to the battery tray.

That wouldn't happen to be a Vacuum hose related to the heater and cruise controls, would it...?

Cause if so, I may have had an idiot moment.

I don't see how a hose to the battery tray would be vacuum, are you sure that wasn't just a drain line in case of battery leak?

BorderWalker 01-31-2018 08:06 AM

It had no visible outlet to collect fluid in case of a leak, and it went upwards from the battery tray, not down. Seemed to go back towards the firewall.

GOLDWING 01-31-2018 08:38 AM

There is a vacuum reservoir under the battery tray.

GW

1996maroonzjf 01-31-2018 09:55 AM

Quote:

Originally Posted by 1shotleft (Post 39622706)
I don't see how a hose to the battery tray would be vacuum, are you sure that wasn't just a drain line in case of battery leak?

There is a vacuum reservoir integrated into the battery tray. It holds vacuum while the engine is off.

1shotleft 01-31-2018 10:07 AM

Quote:

Originally Posted by 1996maroonzjf (Post 39623314)
There is a vacuum reservoir integrated into the battery tray. It holds vacuum while the engine is off.

See how much I'm learning. [emoji106]

GOLDWING 01-31-2018 11:17 AM

Quote:

Originally Posted by 1996maroonzjf (Post 39623314)
There is a vacuum reservoir integrated into the battery tray. It holds vacuum while the engine is off.

While this is true, there is a check valve that holds the vacuum, the purpose is to keep vacuum sufficient to operate the cruise control while climbing long grades. At greater loads are put on the engine the vacuum of the engine tends to decrease and the reservoir helps supply it.

GW

BorderWalker 02-01-2018 08:29 AM

Lesson learned folks. When your putting everything back together, TRIPLE CHECK EVERYTHING.

I felt around blindly for that hose I mentioned. Turns out I had forgotten to plug it back in. Once I wiggled it onto the nipple on the underside of the battery tray, suddenly my vents were working perfectly and Cruise was back in action.

GOLDWING 02-01-2018 09:29 AM

Quote:

Originally Posted by BorderWalker (Post 39628242)
Lesson learned folks. When your putting everything back together, TRIPLE CHECK EVERYTHING.

I felt around blindly for that hose I mentioned. Turns out I had forgotten to plug it back in. Once I wiggled it onto the nipple on the underside of the battery tray, suddenly my vents were working perfectly and Cruise was back in action.

I would agree and add one thing.....

When you've finished a repair on your ZJ and then coincidentally you have a different problem, take a look at the things you just worked on. Chances are you created the second problem while working on the first problem.

GW

digdug18 02-23-2018 10:08 PM

does anyone have a layout for where all the vacuum lines go to and from? I'm guessing that I've the same problem, as my vents change on their own.


The time now is 05:54 AM.

Powered by vBulletin Version 3.8.8
Copyright ©2000 - 2019, Jelsoft Enterprises Ltd.

User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.