2002 QX4 A/C only blows cold during acceleration

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Hey there, I've been a member for a couple years now and had to post finally. I searched the site for my answer and couldn't find it. The ac started blowing warm air while driving even though the ac was set at "cold" and 65 degrees. After 15 mins, ac would begin to operate as designed. Gradually the time for blowing warm air increased, and R134 pressure is fine as I've been monitoring it for a couple months and have no leaks. I learned that if I pushed "off" followed immediately with "auto" on the control panel, sometimes the ac would begin to blow cold. This has gone on for a few months now and seems the only fix now is to floor the accelerator while going downhill, and that is now only working sometimes. I ran some tests and noticed that the compressor is engaged and disengaged as required at idle and in park per FSM. I ran the self diagnostic tests in the FSM and most everything seemed to work properly except one sensor, either the "in-vehicle sensor" or the "sunload sensor" read about 20 degrees higher than the other sensors which all read ambient temp~78 degrees. Any info or further questions would be greatly appreciated. Thanks Corey

[Q451990]

to NICO Corey!

I would think a sensor reading higher would cause the compressor to run more, not less - but that's just a wild guess.

I'm kind of at a loss if the pressures are good and the compressor is engaging as it should... how are you checking the pressure?

Heath

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Thanks for the welcome and prompt response. I agree, if the sensor thought the ambient temperature was hotter than actual, I would assume the system would blow colder. I used a manifold gauge to test pressure. Another thought I had was a possible vacuum issue since under a very heavy load, the ac tends to go from blowing warm to ice cold in 5-6 seconds. As far as a vacuum leak, I wouldn't even know where to start digging. Also about the refrigerant, if I had a leak, i think I would lose cold air completely after a couple months. I am absolutely stumped!

[Towncivilian]

Welcome to NICO!

If you can narrow which sensor reads high, you can replace the part in question. Here are the part numbers for both:

• [27705] SUNLOAD SENSOR
• [27054M] SENSOR-INCAR

Follow the self-diagnostic procedure on page HA-44 to help narrow down your sensor; see steps 5 and 13 in particular.

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By the way, I am trying to be very detailed in my explanations, not to be long-winded, but to hopefully help members in the future when we get to the bottom of this.

[Towncivilian]

That's not a problem! It's better that way.

The most common failure of the automatic A/C systems on Pathfinders and QX4s is the fan control amplifier, which results in the blower motor not turning on. I haven't heard of either the in-car sensor or sunload sensor becoming faulty; I do not think this is the case with your issue, however. This thread describes the fix.

This isn't mentioned in the factory service manual, but try setting the headlight switch to "AUTO" and see if the headlights are always on or always off in the sunlight. The sunload sensor is also used by the automatic headlight system. That might help determine if the sunload sensor is faulty. EDIT: Oops, disregard that. I am mistaken. Sorry.

[[email protected]]

Awesome guys, I will figure out which sensor and start there if that sounds like the best place to start. Thank you for the link to FAQ's Towncivilian. I will still be checking thread for more angles.

[Towncivilian]

Oops, I am mistaken about the sunload sensor and the automatic light sensor. Turns out they're two separate sensors, right next to each other.

EDIT: Oh, hello, fellow Floridian

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That's ok. I noticed they were separate and assumed that's what your edit was. Someone at autozone said a possible problem could be the A/C expansion valve, but I have not yet looked in to that. I would rather take a little more time and start simple and inexpensive and if I have to work up to tearing down the whole system.

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Hey Folks, I just wanted to follow up on my original post. The a/c is fixed:) This is what happened:
I did some more research and all electrical components and sensors checked out. With the fact that heavy acceleration seemed to cause cold air to blow, I pulled out the drier and saw the filter was completely plugged and a tiny rip was in the mesh about the size of a pin hole. I replaced the the drier and expansion valve while I was at it. I recharged the system and voila! Apparently, the acceleration was enough to force the system open though the tiny hole in that filter to allow the system to circulate properly. I also replaced the in-cabin filters which were completely black. The in-cabin filters were previously a dealer only item from what I read, but now can be purchased at most part stores. Thank you to all who helped and your feedback helped me to elimate some processes and save time and money. I hope this helps any future issues. Thanks again. Corey