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H3 A/c issues

H3BigBoy

Member
Messages
9
Location
Texas
I am having an issue with my a/c. Sometimes when I get in and turn my car on my a/c will ONLY blow out the defrost vents. It’s takes like 5 days for it to switch back to the regular vents. My next issue is that it will ONLY blow cold air. I’ve been looking up known issues but having really been finding much. I tried that recalibration thing I saw and it doesn’t do anything. When I did it, the fronts vents blew for like 3 seconds and then switched back to the defrost vents.


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Jeepwalker

Well-Known Member
Messages
857
Location
WI
What happens when you cycle the switch through the different positions? Does it change air delivery locations (vent, heat, defrost) at all? I've had on mine where there was no air to the feet, but moving the switch to vent and back to heat allowed the mode to deliver air to the footwell.
 

Jeepwalker

Well-Known Member
Messages
857
Location
WI
Hmmmm. That's not an area I've had to dig into yet on mine yet. I hope others with more experience can chime in.

1) I guess the easiest and first thing a person should do would be to disconnect the battery and let it sit unconnected overnight. You never know, it might chase away the bugs. That's been known to happen when wierd things like this occur. I know it sounds strange, but it costs nothing. Pull the fuse while the battery is unhooked inspect the fuse carefully ..and ohm it out, make sure no internal corrosion exists (or just replace it). As for the battery cables, clean the terminals and cable ends in the next morning before hooking back up b/c they probably need cleaning anyway. Make sure the small cable to the body is clean and making a good connection too.

If you can get to the BCM connector, might try wiggling that too, in case there's a faulty connection.

2) If you know someone who has a higher end snap on or Tech II scanner they could run the HVAC doors through various 'sweeps' to ensure the damper door motors are working properly and wiring is good to them and all readings and sensors are in accordance. And read any HVAC trouble codes from the HVAC module. If you can read the 'sequence of operation' of the HVAC system in the H3 Factory Service Manual, (below) it 'could' provide some clarity on what's NOT happening. There is a whole sequence of tests illustrated in the manual below to troubleshoot the system, but it takes a good scanner, like a Snap On or Tech-II to do them.


3) If that doesn't do the trick ....and you're the ultra-handy sort with a bit of a grasp on electronics (or willing to learn), you might carefully disassemble the HVAC controller where the dials are ...and look over the circuit board ..if there is one, for any corrosion, cold solder joints, leaked out electrolytic capacitors, etc. If it was me, that's what I would do before replacing anything.

4) If you don't want to take things to those levels, this might be one of those times where it's worth investing 1-2 hours of dealer diagnosis time. ??? My hunch is they're going to scan the HVAC and do the troubleshooting steps listed in the manual. They may have documentation on fixes that show what most fixes are. But if they fix it, might be worth it depending how much work you want to put into it.

https://schwarttzy.com/wp-content/uploads/2013/01/Hummer-H3-HVAC-1-4-1.pdf

Beyond that, I'm kind of out of ideas. Hope others can chime in. Good luck!
 
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Jeepwalker

Well-Known Member
Messages
857
Location
WI
Ok, after reading through the HVAC section of the manual (above link), you may want to check the Mode Actuator. Here's what the description reads from the manual:

"The mode actuator is a 5-wire bi-directional electric motor that incorporates a feedback potentiometer. Low reference, control A, control B, 5-volt reference and position signal circuits enable the actuator to operate. Two control circuits enable the actuator to operate. The control circuits use either ground or a 12-volt value to coordinate the actuator movement. The HVAC control assembly reverses the polarity of the control circuits to move the actuator in the opposite direction. When the actuator shaft rotates, the potentiometer's adjustable contact changes the door position signal between 0-5 volts. The HVAC control module uses a range of 0-255 counts to index the actuator position. The door position signal voltage is converted to a 0-255 count range. When the module sets a commanded or targeted value, the control circuits are energized to rotate to reach the commanded value. As the actuator shaft rotates the changing position signal is sent to the module. Once the position signal and the commanded value are the same, the module opens the control circuits."

There's a chance it's crapped out or a bad connection. I've replaced several damper actuator motors in Grand Cherokees over the years. They do fail from time to time.
 
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Traxx

Well-Known Member
Messages
682
Location
PNW
If the hvac reset doesn't work then likely it is a blend door, both common enough issues.
 
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