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Air conditioning pressure rising to 31 bars at low speed

07-19-2022, 09:13 AM
Dear All,

I live in Rome (Italy) and I'm bit of an hobbyist and DIY type of person and like to service my car as far as my equipment, knowledge and time allow me.

I own a 2016 Nissan Xtrail ("Rouge" in the USA) with 1.6 turbo diesel engine (probably not availabe in North America).
The air conditioning would stop cooling from time to time. I could hear the clutch disengage. No errors on display. I thought that maybe it needed a refill so I took it to a dealer who hooked up the equipment and the cycle was completed (recovery, vaccum, check leaks, refill and what not). Apparently only 34 grams where missing from the 500g of HFO123yf gas.
This did not improve the situation.
It took a few hours to determine with 100% of accuracy that the air conditioning works absolutely fine as long as the vehicle is rolling (even at idle speed downhill in neutral) above 40km/h. Not a single hicup even after 100 miles in 100F degrees at noon. The air conditioning disengage at lower speeds and I noticed, using my motorcycle OBD interface and an iPhone, that above 40km/h refrigerant pressure is always around 7-8 bars. Below that speed, it reaches quickly 31 bars and it disconnects and eventually reconnects at around 20bar of pressure.
I checked the condenser and the fins are not bent nor clogged with. Internal thermistor resistance is around 1.6kohm and climbs to 2.2 when exposed to 60F (15 Celsius) temperature.
I tried to gather some data trying to find some correlation but besides vehicle speed/pressure everything else seems to be consistent. The OBD cheap device may not be able to capture everything so maybe I 'm missing something.
I'm attaching a screenshot of a report I built using the refrigerant pressure top left, pressure sensor tension top right, vehicle speed bottom left and engine coolant bottom right.

I would expect a clogged condenser to underperform no matter and same thing for the evaporator valve/orifice.. The only apparent thing impacting the air conditioning is the flow of fresh air from the front. Could a pressure sensor be out of spec and sense a small increase (due to the reduced cooling at lower speed) as a red zone pressure increase?
I 'm out of ideas (and so is the dealer)...:frown:

Any suggestion is greatly appreciated.



07-21-2022, 08:07 AM
Welcome to the forum! I noticed the x-axis in the lower right, radiator temperature, appears to only show 30 seconds of data but the the other plots show more like an hour and a half. Do you have the coolant temp data which corresponds to the rest of the plots? Also, do you know where that coolant temp data is taken from - is it at the radiator or is it from the coolant temperature sensor on the engine?

Also, do you have access to show when the cooling fan is running, assuming your 2016 Nissan uses an electric cooling fan. Maybe your cooling fan is not working properly, allowing the system pressure to spike when your vehicle speeds are low, or your car's computer to shut off the A/C when the vehicle speed is slow and the coolant temperature begins to rise.


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