2008 Pathy Climate Control Bad

[pathycostarica]

Thanks for reading and any advice.
2008 Pathfinder 4.0 140,000 miles
In cold say 30*F temp the air from the vents will blow cold after a while unless I put the temp up to max 90. Then it gets so hot in the cabin that I turn it down to 87 and it starts blowing cold until it gets too cool (yes at 87) in the cabin and only putting it back to max 90 gets it to blow hot again, but then it’s too hot quickly and this keeps going on and on. In. 2 hr drive I will have to keep doing this up and down 20-30 times. Dangerous, frustrating, I really want to fix this.
I have bled the cooling system correctly I believe with car on a very sleep upward hill, cap off coolant tank and 15 min constant at high rpms.
The A/C button light comes on as soon as I touch the temp dial no matter the settings so I turn that off.
I have tried other various things with the buttons but with no help.
I am in FL now, not in a cold climate but maybe someone has this experience and knows or can take a good guess at what the issue is? This has been going on since I got the car 2 years ago and I can’t find any threads that are like this.
Thank you for any advice. So greatly appreciated.

[VStar650CL]

In a Nissan Auto A/C system, 89~90F and 60~61F are "magic numbers" that basically tell the HVAC, "Make it as hot or cold as you can and ignore the sensors." There are three sensors the A/C Auto Amp uses to regulate temperatures in between, and wacky or non-linear behavior in the system is almost always because one of them is dead or malfunctioning. There's an ambient sensor in the grille (there are actually two, the one with Violet and White wires is for the HVAC), an In-car sensor near the driver's right knee, and an Intake sensor mounted directly on the A/C evap. The latter is trouble if it's bad, because the dash and HVAC need to come apart to replace it. The other two are pretty easy. See pages 8~10 here for the locations of HVAC components on your Pathy: https://www.nicoclub.com/service-manual ... %2Fhac.pdf

The simplest way to find out if one of them has a problem is a scanner that can detect and talk to the HVAC. It doesn't need to be a Nissan Consult3+, any good repair shop will usually have a Snap-On Solus or other high-end scanner that can do the job. The A/C Auto Amp can stream the sensor temperatures, so you simply read them and see if they correspond to reality. The Ambient and In-car sensors should correspond more or less to the temps outside and inside the car, the Intake sensor should read in the low-mid 30's with the A/C running and a bit below ambient with the A/C off. Note that the Ambient is always very heavily "damped" and may take up to 30 minutes to adjust when coming into a garage from cold or heat.

[pathycostarica]

VStar,
Thank you for the extreme knowledge. I will have my friend scan with his Snap On when I get back to NY in 3 months. Hopefully it’s one of the 2 easy ones.
If it is and I change one or both, is there any type of calibrating or reset needed? Or can I just change them and good to go?
Thanks

[VStar650CL]

You're most welcome. No calibration needed, they're all plug-and-play. You might want to have a quick look at the Ambient sensor through the grille, it's very common for rocks or road debris to hit the sensor or wiring harness and disable or damage it. Rodent damage to that stuff isn't uncommon either.

[pathycostarica]

That’s great. While I am away and not near a code reader I may just see what the sensor costs and if not bad just swap it out.
Thanks again. I’ll let you know how I make out.

[pathycostarica]

Hi VStar650cl,
found both sensors like you said and pretty easy to get at. The ambient one in the grill I got a part number of 27710-31u00. My problem is the in cabin one next to the ignition key I can't find a part number. I have been on the phone with local Nissan parts dept and he can't find a part number or even a diagram from the manual that you linked me to that was very clear to see. Any idea how I can find the part number for that sensor?

thanks

[VStar650CL]

They only show one current part number for it on an '08, 27720-9CH0A. The exact description is "SENSOR - IN CAR".

[pathycostarica]

thank you so much

[pathycostarica]

update and I think fixed:
I changed the "in car sensor" 27720-9CH0A to the right of ignition key and it seems to have solved the problem. Unfortunately I really wont know until I go back to NY and a colder climate in April. But what I found when I pulled out the old sensor and looked at it carefully it was full of lint all over the thermal sensor which is a small electrical component like a resistor. The whole sensor has a 1" squirrel cage fan wheel inside it like the in car blower. This also was all full of lint I assume from 15 years of spinning and sucking the crap from the cabin into it. Thus it was barely able to spin when i blew on it. The new sensor spun free that it kept spinning for 5-10 seconds. I do wish I had now taken it out and inspected it, then cleaned it and tried it again. However I am very happy to have found it likely in a state of not working so hopefully this is and was the problem. If any one comes across similar symptoms I suggest checking this and cleaning it up, carefully as it seems a fragile thing.

I also changed the ambient temp sensor in the grill anyway as I had ordered that too. having driven the car earlier and the actual outside air temp being about 65 the "outside temp" showing on the cars screen said 84 but I figured it was due to the heat off the motor and rad. Yet I put in the new ambient sensor hoping it would now read closer to 65 but the screen still said 84? why this is or if there needs to be a reset done like I have seen in some videos I dont know. I wont do anything until I see how the climate control heating and A/C work over the next days and maybe until April when I get back to colder NY temps.

Many Many thanks to VStar650cl as I would not have seemingly fixed this without you. Priceless really. And I hope this helps anyone else who has similar symptoms.

[VStar650CL]

I also changed the ambient temp sensor in the grill anyway as I had ordered that too. having driven the car earlier and the actual outside air temp being about 65 the "outside temp" showing on the cars screen said 84 but I figured it was due to the heat off the motor and rad. Yet I put in the new ambient sensor hoping it would now read closer to 65 but the screen still said 84? why this is or if there needs to be a reset done like I have seen in some videos I dont know. I wont do anything until I see how the climate control heating and A/C work over the next days and maybe until April when I get back to colder NY temps.

You're most welcome, happy to help. See if the outside temperature corrects itself after sitting overnight. You'll never see an immediate change unless you remove battery power from the HVAC. That's because of "damping" in the HVAC software, which only allows the reading to change at a maximum rate of about 10F per hour. Note also that the temperature in the rearview mirror comes from the "other" ambient sensor in the grille, so that one won't correspond to the HVAC sensor.

[serezka21]

The air temperature sensor in the cabin, which is installed under the ignition lock, near the driver's right knee. Usually the fan gets dirty there. It is enough to blow it or rinse it and everything will be fine.