2018 Rogue SL - AC fails when going from 5600 feet to sea level

[Flashfox]

2018 Rogue SL, ~46,000 miles, always maintained at the Nissan dealership.

I need to go up to a mountain site every month or so. This location is at ~5600 feet. When I head there, I have no issues. However, when I return, I lose AC when I reach ~800 feet. It remains a problem until several hours or the next day.

I had brought the vehicle to the dealership to have it checked a few months ago and they found nothing as the AC worked.

Yesterday, on my way back from the mountain, I had the problem and drove it to the dealership. They had their AC main tech/manager come and have a look and he took pictures, notes and saw what was happening. I am scheduled to bring it back on Wednesday ... but as the AC is now working fine, I am, concerned that they will find nothing even though they saw what was happening.

Both CoPilot and ChatGPT AI platforms and the Nissan tech said that it looks like a pressure sensor as the problem goes away after a few hours as the pressure is equalized. He also speculated on something else as the air was cool BUT the airflow was practically non-existent, even with the fan at max (closed flap?). However, he did not understand why it would only happen on the way down and why it corrects itself the next day. Could be erroneous sensor info sent the the ECU? Note that this morning,the AC was working just fine.

I bought the OBDLink MX+ as it was recommended on CoPilot and ChatGPT. I also paid for the Nissan Enhancement, which is supposed to support the AC Pressure sensors. I hoped to look at AC high Pressure PSI and Voltage, and AC Low pressure PSI and Voltage, the Compressor control and environmental inputs (BARO, evap temp). I wanted to build a custom dashboard but those measurements were not available (sigh). And yes, the Nissan Enhanced module was purchased and the app confirms that.

So I now turn to this forum ... any ideas what "sensor" or issue could be causing this?

- AC works fine everywhere even when heading up the mountain to the ~5600 feet level
- AC fails coming back down when I reach ~800 feet level
- AC works again after several hours ... no issues any day even on very hot days

This all seems like a pressure sensor sending erroneous info to the ECU ... but which one?

[VStar650CL]

The blocked airflow is the smoking gun, your evap is freezing up from a bad TXV Valve. TXV's almost always fail open (sensible, since they're basically a reverse thermostat). When they do, they allow too much refrigerant through the evap which in turn becomes a block of ice. That kills the airflow and the ice just gets thicker till the car or A/C is shut off and the ice can melt. In your case, the extreme change in pressure and temperature on the downhill is probably exacerbating it.

I should add that TXV's are a very common failure item on gen2 Rogues. We change a lot of them.

[Flashfox]

Thanks VStar ... I'll share this with the NISSAN service when I bring he Rogue in on Wednesday.

I do wonder why this is only happening when I go from 5600 feet to 800 feet? If tthe valve was bad I would assume that I would see this problem more often, not just during the trip down the mountain's very winding roads (30 mph max)

[VStar650CL]

I'd check the amount of refrigerant in the system, because a low charge lowers the boiling point of the refrigerant and could be contributing to it. However, that's exactly what the TXV is supposed to prevent. So it's probably just a unique combination of pressure, temperature, and humidity combined with a valve which isn't quite right and an engine that's spending most of its time coasting. Regardless of the proximate causes, in an otherwise healthy system, you can count the things which ultimately cause a frozen evap on one finger. Nothing but the TXV can do that.

[Flashfox]

Thanks again ... I will share this and report back after Wednesday's visit to Nissan service

[VStar650CL]

PS - I'd have them check for a restricted drain hose too. The evap is at the front of the HVAC box on your Rogue, and a slow drain could cause it to end up partly immersed on a continuous downhill. That in turn could reduce the airflow, which will definitely contribute to a tendency to freeze.