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Intermittent loss of air flow in vents

Tiny
CHIROKAT74
  • MEMBER
  • 2000 JEEP GRAND CHEROKEE
  • 4.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 205,000 MILES
Force of air coming out of the vents starts to decrease until you feel nothing but can still hear the blower motor moving air. If I turn it off for a couple minutes then back on, it works fine again. I have to turn the temperature knob into the red to make the AC temperature not ice cold. Also, the intensity of the vents is not the same from one position to another; it is even different side to side. I am waiting on my new blend door to arrive (old one is nasty and dry-rotted) but did not know if the actuator could be part of the problem, or maybe something else? I have already replaced the blower motor resistor to correct the speeds.
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Friday, October 12th, 2018 AT 7:46 PM

23 Replies

Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 43,047 POSTS
The blend door actuator can be causing it, but can I ask if the low air flow happens with both AC and heater? Here is a guide that can help:

https://www.2carpros.com/articles/low-or-no-air-flow-from-vents

Please run down this guide and report back.

Cheers, Ken
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Monday, October 15th, 2018 AT 11:41 AM
Tiny
CHIROKAT74
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  • 19 POSTS
I do not remember it happening with heat but it takes a while before the force starts to dwindle and I was not driving it regularly last winter. The difference side to side is there all the time. I do not have a cabin filter and cannot see any obstructions to the intakes; as for the blower motor, the sound of the force does not change, just that it is no longer making it out of the vents. Is there something on the AC side that would freeze up and prevent flow out of the vents? We occasionally get a drip in the passenger floorboard so the drain line is on my list to check, just have to find a wire coat hanger (no easy task, lol).
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Monday, October 15th, 2018 AT 12:34 PM
Tiny
KEN L
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Yes it does sounds like the evaporator is icing up which causes the air flow to slow down. That is because the AC needs to be recharged. Here is a guide to help you charge the system and a video on how to unclog the evaporator drain:

https://youtu.be/uZrQCGwXfek

and

https://youtu.be/q9_MZiS2_NE

Please run down these guides and report back.

Cheers, Ken
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Tuesday, October 16th, 2018 AT 10:12 AM
Tiny
CHIROKAT74
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  • 19 POSTS
The AC was just serviced this summer by my usual shop, it has actually been doing this ever since they repaired and charged it. I am not getting any real amount of water, just an occasional drop or two. Would that still be the drain line?
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Tuesday, October 16th, 2018 AT 7:44 PM
Tiny
KEN L
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Yes it will be the drain. I think we should check the pressures of the AC system it sounds like that is the problem. Here is a guide to help:

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system

Let me know what the pressure readings are.

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Wednesday, October 17th, 2018 AT 9:55 AM
Tiny
CHIROKAT74
  • MEMBER
  • 19 POSTS
I do not have the kind of equipment to check the pressures, but I will have my mechanic check it since they did the original repair. I just put in the new blend door and the motor moves it all the way down (full cold) but not all the way up (full hot; see attached picture). Is it supposed to stop there?
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Thursday, October 18th, 2018 AT 8:51 AM
Tiny
KEN L
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It could it would still have air flow the fact that it only does it with the AC on after long time on tells us the evaporator is icing up. What happen to the heater box? Looks like you did a modification?
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Thursday, October 18th, 2018 AT 10:06 AM
Tiny
CHIROKAT74
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  • 19 POSTS
The only thing I have done is cut open the plastic to get to the blend door. So the blend door is supposed to stop only three quarters of the way up when the temperature knob is turned all the way to the hot side?
Also, I got under the car to find the end of the drain line and cannot see it. I know it’s there from the tell-tale puddles but I can barely see the firewall from the top side, let alone the bottom.
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Thursday, October 18th, 2018 AT 10:16 AM
Tiny
KEN L
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If the system is auto air then yes the blend door will go to the position and then adjust while in operation. It will not cause low air flow. The tube should be at the fire wall down low on the passenger's side.
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Friday, October 19th, 2018 AT 9:55 AM
Tiny
CHIROKAT74
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Mine is manual, single zone.
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Friday, October 19th, 2018 AT 10:05 AM
Tiny
KEN L
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Is it auto air? Do you set the temperature? Or just hot and cold?
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Friday, October 19th, 2018 AT 11:41 AM
Tiny
CHIROKAT74
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  • 19 POSTS
Just three knobs, hot to cold, speed and vent selector.
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Friday, October 19th, 2018 AT 5:28 PM
Tiny
KEN L
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That is a manual system so the door should go all the way over. Can you remove the blend door actuator to see if you can move the door by hand?
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Saturday, October 20th, 2018 AT 10:32 AM
Tiny
CHIROKAT74
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  • 19 POSTS
It moves fine by hand and will go all the way up; got a new actuator on the way.
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Saturday, October 20th, 2018 AT 6:47 PM
Tiny
KEN L
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Okay let me know what happens.
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Monday, October 22nd, 2018 AT 10:18 AM
Tiny
CHIROKAT74
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  • 19 POSTS
Will do! Any special procedures for connecting the new actuator to learn correctly?
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Tuesday, October 23rd, 2018 AT 3:55 PM
Tiny
KEN L
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Nope should be plug and play.
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Wednesday, October 24th, 2018 AT 10:45 AM
Tiny
CHIROKAT74
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  • 19 POSTS
New actuator is on and it takes the door further up. Of course, now it’s too cold to need the AC but I’ll get the pressures checked this week.
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Sunday, October 28th, 2018 AT 1:35 PM
Tiny
KEN L
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Sounds good please let me know.
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Monday, October 29th, 2018 AT 9:24 AM
Tiny
CHIROKAT74
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My middle console vents still do not blow evenly; passenger one is pretty weak compared to driver’s. The other face vents blow fine. Is there something else I can check for that?
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Monday, October 29th, 2018 AT 10:18 AM

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