Have Jeep Questions? Ask a Jeep Repair Expert for Answers
Hello and welcome to JA.
This could be caused by the A/C evaporator freezing up, which will cause a restriction of the airflow.
Have you tried driving with the A/C compressor OFF, to see if the problem still happens?
Thank you for getting back to me.
The problem is not just when the A/C is going - in fact it is more of a problem in the winter with no hot air flow (windshield freezes over, cabin is cold). [Note: I am assuming that by having the A/C turned OFF (the little snowflake button not lit), that the A/C compressor is off.]
I have read several notices that the blower motor resistor fails on Liberties, but the motor seems to run fine on all speeds. The problem is getting the air from the blower motor fan to the cabin. And the problem only arises during long drives. It works fine on shorter drives.
Thank you, XXXXX XXXXX advise.
The A/C compressor will be engaged if:
One way to verify is to go under the hood and unplug the wire connector to the A/C compressor...that will prevent it from engaging.
Another thing to check on Liberty...pull the glove box door off and inspect the mesh screen on the HVAC case...I see many of these clogged with dust.
Reply back here if you have any other questions or need more detail.
I removed the glove box looking for the mesh screen. The only screen visible appears to be the mesh covering the door that controls re-circulation (this screen was clean). Is there another mesh that I should be looking for?
I have had the same problem regardless of whether the A/C compressor is ON or OFF. Commonly the air flow stops during a long drive if the mode is set to FLOOR (i.e. A/C compressor should not be on)
I am going on a long drive tomorrow (30th). I have replaced the Blower Motor resistor tonight, based information gleaned from other sources. I will let you know if there are further problems.
Please let me know if you have other suggestions, or if I should be checking something else on the Jeep.
You checked the correct screen...that is the only one.
Have a good trip...I will be here if you need anything else.
Blower seems to working now that I have replaced the blower motor resistor, and this appears to have corrected the problem. Unfortunately, this was not advice offered by your website.
Thanks for the follow-up...keep me posted on how it works out.
The blower resistor does not match your symptoms at all...but I am happy that it seems to be fixed, regardless of whether I was right or wrong.
I will be here if you have any other questions.
Happy New Year,
Thanks for following up with me. As you suspected, the blower motor resistor did not correct the problem. On the way back home the air flow stopped again.
The outside temperature was only marginally different during the outbound and return drive, I was not driving any harder or with a heavier load in either direction. The only difference that was noticeable, was that I used cruise control on the return drive when the airflow stopped.
Any suggestions would be much appreciated.
This a strange and unusual problem indeed.
The symptoms as you describe them match evaporator freeze-up EXACTLY.
Have you tried my suggestion I made a few days ago...to disconnect the electrical to the A/C compressor, then drive the Jeep and see if you can duplicate the loss of airflow?
Doing so will eliminate the freeze-up as a possible source of the problem.
Also verify that when the engine is running, that the center part of the A/C compressor is not spinning, which is how it should be when the compressor clutch is disengaged.
Thanks for the thoughts. I will try disconnecting the electrical to the A/C compressor.
Some follow-up questions:
1. Where, in the engine compartment, is the A/C compressor (and it's electrical supply)?
2. How is one certain that the A/C compressor is not spinning? Is it visual, or am I listening for something?
3. When you mention the compressor clutch being disengaged, is this the accomplished by disconnecting the electrical supply to the A/C compressor, or is another step required.
4. If the compressor is freezing up, how do I correct the problem? Install a new A/C compressor?
Sorry for my delayed response: Here is a picture below: (click on it so you can see it full-size)
The green arrows point to the compressor clutch. This portion will not spin when the A/C is OFF. It will spin when the A/C is ON. Run the A/C on LOW blower, full cold, and you should see (and hear) the clutch engage and disengage. This is called cycling and it is normal. If it is very hot outside, it may not cycle.
The orange arrow points to the electrical connector. Slide the red lock over (about 1mm) and then press the black release tab to disconnect. This will disable the A/C compressor.
If it turns out the system is in fact freezing up, it is probably the low pressure cycling switch.
That picture was perfect, thank you for that.
It is -13 degrees Celsius (8 degrees Fahrenheit) today. When I set the blower to low setting with full cold and the A/C button (snowflake) ON, the compressor clutch does not cycle, but is it because of the cold outside temp?
I did see it cycle once for ~3 seconds, but not after that.
I am going to try to repeat the symptoms with the the electrical disconnected from the A/C compressor on Tuesday.
Should I place some electrical tape over both ends of the A/C compressor electrical connectors?
Thank you again for your time.
At that temperature, the A/C won't come on much, but might come on more often as the engine compartment warms.
No tape is necessary, just make sure the wiring won't get caught in the belt.
After a couple of long drives, the air flow has not quit since I disconnected the A/C compressor.
You had said that this may suggest that the low pressure cycling switch is the problem.
Can you think of any other problems, or should I replace the low pressure cycling switch?
How does one go about replacing the low pressure cycling switch?
Thank you for your help.
Below is the best picture I can find. The arrow points to the silver, cylindrical-shaped A/C drier. On the drier, there sould be a 2-wire switch (the low pressure cycling switch). To replace it, unplug the connector and use a wrench to loosen and remove the switch. Only a tiny bit of refrigerant will come out, not enough to worry about. Replace the o-ring...should come with the new switch...put a drop of engine oil on the oring...do not overtighten the new switch.
I cannot promise you that the low pressure switch will fix the problem, but from where I sit, it seems to be the most likely cause.
Another thing to check is to verify that the a/c compressor is only engaging when it is supposed to---when the snow flake button is pressed, or when the selector is on defrost. In other words, verify that the comressor is not engaged at all times. This may be a bit more difficult if it is very cold outside. A/C is much easier to diagnose when it is warm or hot outside.
The final thing to check is that the system has the proper refrigerant charge. A repair shop will have to do this. They can evacuate the system and the machine will show how many pounds of refrigerant the system had in it. Then they will recharge it with the proper amount.
The dealer service information is calling it "A/C low pressure cut off switch".
Do you have a Jeep dealer close by?
Hello, just checking in with you.
Any progress or new info?
Thanks for checking up on me.
On Friday (8th) I was able to find a dealer who knew what the part was I was looking for. It will be delivered to the dealer today, and I will try to install it tonight or tomorrow. I will be towing a trailer this weekend so we will see if it was this switch.
If there is no success I will send you a note to see which of your other suggestions you think I should try next.
OK, I will be here.
Next, I recommend to have a shop evacuate and recharge the A/C system to verify that it has the correct amount of refrigerant in it.
Please tell me...on these long drives...when the low airflow problem happens...what are the settings on the HVAC panel (fan speed, mode, temp) ?
Generally the HVAC is set to:
Temp = Hot (or ~80% of full hot)
Mode = Floor
Fan Speed = 1
I will see if I can find a shop to recharge the A/C. Can the A/C be system be checked for the proper amount of refridgerant prior to draining and/or refilling, or is there no way to tell, and it can only be re-filled?
Any thing else I should ask at the shop to make sure I am getting the correct service?
The problem I'm having here is....with the HVAC on that setting...the compressor should not engage at all (unless the snowflake button is pressed). And if the compressor is not engaged, then the lack of airflow cannot be due to evaporator freeze-up.
I think the next step is to verify that the compressor engages only when you choose a setting that normally engages the compressor...
To answer your question about the refrigerant check....it depends who you talk to. Some techs will say you can check the level by reading the gauges which are connected during service. I say you cannot...because the readings vary from car to car, and also vary with ambient temperature. The way I do it is to recover the refrigerant with an A/C service machine. It weighs the refrigerant that is recovered. Then you compare that to the sticker under the hood which indicates the correct system capacity.
Thank you for the info about the refridgerant.
I read your comment that the compressor should not be engaging and took a look at the compressor clutch today. I was only driving around town - i.e. short drives, but when I opened the hood, the compressor clutch was sporadically engaging. Is this of concern, or of note? Or is this normal?
Thank you, again.
The settings were:
Temp = Hot
Fan Speed = 2
Snowflake button = OFF
It appears the A/C compressor is engaging when it is not requested or needed.
Let me see what I can come up with.
Open the fuse box underhood. Locate and remove the a/c compressor clutch relay. The underside of the lid should show the location. Mark this relay with a piece of tape or something similar. Choose another relay in the fuse box and install it in place of the relay you removed. In other words, swap the relays around. Retest for the same problem.
Other than that, I am running out of ideas. It appears the a/c compressor is engaged at all times, except for when it normally cycles on/off. A signal from the HVAC control head is an input to the engine computer. Then, the engine computer directly controls the a/c clutch relay.
It may be necessary to have the vehicle checked by a competent electrical technician who has access to the proper scan tool for diagnosis.
This could be a problem with the HVAC control head, or the engine computer.
no cold air blowing out when ac is on but low pressure