HVAC issues... where would you start?

durangotang · **Posted:** Sun Dec 20, 2009 12:45 am

Here are the symptoms:

When the vehicle is cold everything works how it should. At some point during driving after it's up to temp, air stops blowing out of my selected vents (doesn't matter what I switch it to: AC, defrost, heat, recirc, etc). Air just seems to trickle out of all the vents when this happens. Temp still adjusts properly. I can here the typical "thunk" in the HVAC box when I switch to/from defrost, blower speed still changes properly.

This happens every time the KJ gets warm... where should I be looking? I've picked apart the FSM but can't seem to pinpoint things. I'm just going to replace the cheapo vacuum one-way valves on the firewall (being as they cost practically nothing)... any help out there? :dizzy:

2006 KJ · **Posted:** Sun Dec 20, 2009 2:00 pm

i posted this about mine a few weeks ago and didnt get much help with it... i'm either going to rip it apart soon or get it to the mechanic (he's extremely good at figuring things like this out). but mine is doing the EXACT same thing except it takes mine about 45mins to stop putting anything out. i think it might be something wrong with the door.

if you find anything out let me know... and i'll do the same.

here was mine... might help you some

viewtopic.php?f=1&t=47271

ATXKJ · **Posted:** Sun Dec 20, 2009 3:14 pm

I vote for the blend door (or blend door actuator)
no good ideas on how to test it other than start poking around in the plenum
you might be able to see a lever or connection

boonsur · **Joined:** Mon Jan 04, 2010 2:24 pm **Posts:** 4

Did either of you find-out anything/solve-this?

I've got the same issue - works great for about 15 minutes, then kicks out. Can still feel warmth from the vents, but can't get any air movement. Funny thing is, mine will kick back-in after a while???

I don't have a garage (and it's been pretty cold/lots of snow), so I haven't been in the mood to tear into things, blindly.

durangotang · **Posted:** Thu Jan 07, 2010 8:25 pm

I haven't had the time to tear into it... too busy tearing into everything else :lol:

LibertyFever · **Posted:** Thu Jan 07, 2010 10:37 pm

I have a PDF that details the various parts of a 02 KJ that might be useful in sorting out the vacuum lines.
PM me with an email address and I'll send you a copy (under 9 meg in size)

Jeepjeepster · **Posted:** Thu Jan 07, 2010 11:01 pm

Mine did this once for around 10min and its never done it again. Blower works, air selection works, temp works. Idk what else there is that could go wrong. Its like there another blend door that just blocks off the air flow.

boonsur · **Joined:** Mon Jan 04, 2010 2:24 pm **Posts:** 4

I think I've got a good, working theory.

As a side (but maybe important) note, my A/C clutch is kicking on-and-off a LOT. Found a line in the FSM that says this indicates low refridgerant in the system. Didn't seem important at the time (why worry about A/C in the snow).

Last night, while it wasn't producing warm air, I popped the hood to check the coolant hoses for water pump/thermostat operation.

I immediately noticed that all the A/C lines were severely frosted-over.

It would stand to reason that the evaporator is also frosted/frozen over. Again referencing the FSM, it looks like ALL airflow has to pass thru the evaporator (even on recirc.). If it's blocked (frozen), then no airflow! Can still feel heat, because the heater core is on the downstream side, so it is still warming the air.....a little.

I almost always have it in defrost mode (need to, to keep the winshield from fogging).....which (duh) utilizes the A/C pump to "dry" the air.. This morning, I drove-in with the selector only set to the vents and floor, and voila, I had heat the entire trip!

So, I'm hoping a refridgerant charge will cure it! I'll try this weekend, to know for-sure.

Just hoping I don't have any leaks in the system (BTW - is there any common areas to check for leaks?).

durangotang · **Posted:** Fri Jan 15, 2010 4:28 pm

boonsur wrote:

I think I've got a good, working theory.

As a side (but maybe important) note, my A/C clutch is kicking on-and-off a LOT. Found a line in the FSM that says this indicates low refridgerant in the system. Didn't seem important at the time (why worry about A/C in the snow).

Last night, while it wasn't producing warm air, I popped the hood to check the coolant hoses for water pump/thermostat operation.

I immediately noticed that all the A/C lines were severely frosted-over.

It would stand to reason that the evaporator is also frosted/frozen over. Again referencing the FSM, it looks like ALL airflow has to pass thru the evaporator (even on recirc.). If it's blocked (frozen), then no airflow! Can still feel heat, because the heater core is on the downstream side, so it is still warming the air.....a little.

I almost always have it in defrost mode (need to, to keep the winshield from fogging).....which (duh) utilizes the A/C pump to "dry" the air.. This morning, I drove-in with the selector only set to the vents and floor, and voila, I had heat the entire trip!

So, I'm hoping a refridgerant charge will cure it! I'll try this weekend, to know for-sure.

Just hoping I don't have any leaks in the system (BTW - is there any common areas to check for leaks?).

Awesome... keep us updated on that. I never thought about the refrigerant. I had my money on a stuck blend door or blend door actuator :juggle:

adamkrz · **Posted:** Fri Jan 15, 2010 11:34 pm

Good call by boonsur, Low refrigerant will cause the coil to freeze and block airflow, The same thing happened to another vehicle i had owned some time back.

boonsur · **Joined:** Mon Jan 04, 2010 2:24 pm **Posts:** 4

Just an update - Not solved yet - Still working on it.

I checked last weekend, and my system is/was fully charged (so it wasn't low-fill causing the freeze-up).

Studied the FSM some more, and I think the "A/C low pressure" switch is faulty. It's purpose is to shut-down the system when it's low on refridgerant. In addition, it is supposed to open the contacts when the ambient air temperature drops below ~34*F. This will disable the a/c compresser and prevent the system from freezing-up. Since mine is trying to run, even when the air temp is below 0*, I think the switch is puked.

I was hoping to swap the switch and have better results to report, but my dealer has been failing me miserably ("forgot" to order it). Hopefully they'll get it in today, but I'm not sure if I'll have time to work on it tonight.

adamkrz · **Posted:** Wed Jan 20, 2010 4:39 pm

It would also be an easy fix changing the pressure switch,Just unscrew the old one and replace - it has a scrader vavle so no need to remove the refrigerant.

Jeep Dawg · **Posted:** Sat Jan 23, 2010 12:39 am

the problem is blend door actuator

boonsur · **Joined:** Mon Jan 04, 2010 2:24 pm **Posts:** 4

No, the blend door is working fine (in my case). I get heat (fully adjustable temperature) all day-long, when I leave it in "vent" and/or "floor" directional modes. My problem is the A/C evaporator freezing over (frost blocking air flow).

I finally got, and replaced the low-pressure switch. However, it is still reading "closed" (continuity) on the vehicle, in 20* temps. And thus, the compresser is still kicking-on.

When I got the old switch out, it checkes "open" (non-continuity), on the bench. This leads me to think my system may be overcharged. I'm going to try bleeding it down this afternoon, to see if the switch will flip to open.

Please stand-by.......

durangotang · **Posted:** Sun Jan 24, 2010 2:08 am

Very cool... thanks for jumping into this...

I eagerly await your findings....

durangotang · **Posted:** Fri Jan 29, 2010 3:16 pm

Any news?

MonsieurGlen · **Posted:** Sat Feb 06, 2010 2:15 pm

Please keep us updated on this. I was having the same problems as boonsur. My temp solution was to unplug the power to the A/C compressor until I can take it to the shop. This is fine since we have been having a cold winter but I will definitely have to get it fixed before the heat and humidity come back this spring.

durangotang · **Posted:** Thu Feb 11, 2010 7:20 pm

MonsieurGlen wrote:

Please keep us updated on this. I was having the same problems as boonsur. My temp solution was to unplug the power to the A/C compressor until I can take it to the shop. This is fine since we have been having a cold winter but I will definitely have to get it fixed before the heat and humidity come back this spring.

Did you pull a fuse for the AC compressor? Which one?

MonsieurGlen · **Posted:** Fri Feb 12, 2010 11:20 am

durangotang wrote:

MonsieurGlen wrote:

Please keep us updated on this. I was having the same problems as boonsur. My temp solution was to unplug the power to the A/C compressor until I can take it to the shop. This is fine since we have been having a cold winter but I will definitely have to get it fixed before the heat and humidity come back this spring.

Did you pull a fuse for the AC compressor? Which one?

No, I popped the hood and unplugged the compressor completely. The wires are connected right on top. IIRC you have to slide the little red thingy and either push down or lift up on the black tab to unplug it. Then I (MOST IMPORTANT) clipped the wire bundle to the other bundle next to it so that it doesn't get caught in the belt :grim:

.

durangotang · **Posted:** Mon Mar 08, 2010 10:49 am

Just to let everyone know... it is an AC problem.

If you pull the fuse under the hood for the AC clutch the problem goes away... (along with your AC). Just don't forget to plug it back in periodically and let the compressor run.

Now it's time to figure out the problem with the AC.... hmmmmm

HVAC issues... where would you start?

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