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Hi guys,

OK. I've started getting this issue on longer drives (+2 hours). The AC works fine and then the cabin temp starts to increase without any interaction with the system. This has occurred a couple of times now. The fan still operates but there's very little airflow from any of the vents regardless of what mode is selected.

The first time, the system righted itself while it was parked up. The second time, I tried disconnecting the battery for a couple of minutes to reset the system but that didn't work so I did a little research. The schematic suggests that the only single damper (or 'door' as Nissan calls them) that can have this effect is the 'Upper Air Mix Door' which, together with the Lower Air Mix Door, controls air temp by directing a portion of airflow via the heater matrix as required. If this is shut as well as the Lower Air Mix Door, no airflow can enter the cabin. With this in mind, I was going to test the theory by increasing the temp setting to max to force the Lower Air Mix Door open to allow airflow through the Heater Matrix into the cabin. However, when I attempted this, the system was working fine again! Frustrating, I know. I now have to wait for it to fail again before I can investigate further.

The car is still under warranty but there's not much point taking it to the dealer unless there's actually something wrong with it. I guess I'll have to wait until the failures become more frequent or it fails altogether but with ambient temperature here regularly in the late 30s to early 40s (deg C) that's a prospect I'm not looking forward to!

So, I'm thinking there's either something mechanically wrong with the Upper Air Mix Door which realigns itself after a while or possibly the first signs of a failing A/C Auto Amp which drives all of the dampers (doors) in the system

Since the AC system doesn't respond to an increase in cabin temp by increasing fan speed (in auto) I'm thinking that it's the A/C Auto Amp.

I welcome anyone's thoughts on this.

Thanks

Ady
 

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old thread I know ...but I have this exact problem on my 2010 T31.... after about 1.5 - 2hrs of use. Blower fan is still turning fast ..can hear it ..but there is very little airflow out of vents. Now...I never thought about it being a problem on the Inlet side of things, BEFORE the fan .... so I concentrated on the outlet side...AFTER the fan ..and actually there is very little that can obstruct between fan and vent..just filter..and evaporator or heater matrix.

Its not my filter..its new...so Im thinking the evap is freezing?? .... fan working fine..but no airflow can get thro the evap... cos its iced up? ... Ive
checked and double checked all the sensors...like evap inlet temp sensor..this is what tells AC auto amp to de-clutch the compressor when temps get too close to freezing... it measures ok ...and it compares ok with a new one. Compressor is cycling ok when I disconnect the sensor ..so the auto amp seems to be doing its job....

after researching online .. it seems that low refridgerant pressure is a common cause of icing up...so they say anyway ...gonna get my refrigerant pressure checked. When it works the airflow is cold ... but still gonna get pressure checked first opportunity...if only to cross it off the list.

Also..like the OP ...mine fixes itself after about 10mins turned off ....which again points to freezing evap. defrosting naturally. I do notice A LOT of condensate under the car too after its switched off ..more than is normal I think ..again points to defrosting. Next time it happens while driving I'm gonna manually sw. off a/c ..keep blower fan at max and open the flap for outside air .... that should defrost the evap. quickly. If this does the trick..and good airflow is restored...then Im pretty sure it must be evap. icing caused by low pressure refrigerant....

Like the OP tho ...I have to wait for it to fail before I investigate or diagnose further ...and that means doing long drives... its very frustrating indeed.
 

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well I finally managed to get the refridgerant pressure checked ..and it was fine .. ? ....so ...im no further forward ... everything seems to work fine..until 1.5 - 2hrs ...then ..no airflow.

gotta take the dash apart again..and check n re-check everything ....

possibly some dry solder joint inside the Auto amp is the culprit ..... might have to get that out and split it...

I much prefer manual a/c systems .... seldom get any of these kind of problems ...
 

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Sounds to me like your evaporator is freezing up and becoming a block of ice. My guess is conditions are very hot and humid, and the air con is always set on fresh air from the outside. Does it do the same thing if you keep the air setting on recirculate, as that would put less load on the system. Possibly linked to clogged cabin air filter that is restricting air flow?
There is no point taking your dash apart if you are getting normal ac for the first two hours of a long drive in +30C temps, as the system obviously works. At least that is my take.
 

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..I too, reckoned it was a freezing evap. causing the problem. I normally drive it in recirculate...very seldom on fresh air ..unless it was on Auto perhaps and had opened that outside flap without me noticing ..unlikely, but possible.
In any event..the evap sensor & auto amp should prevent a freeze up...i think it's that system that is failing after 1.5hrs....
The cabin filter is brand new so I dont think that is the issue ..and as I say..works fine for the first 1.5hrs or so.
The evap sensor measures ok..and its resistance varies as it should.
That really only leaves the auto amp ..that is maybe failing after 1.5hrs ...and not cycling the compressor as it should when the evap temp gets too low....
gonna get it out and take a look at the board...see what I find in there...

be nice to know if the OP got anywhere
with his problem....
 

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Not sure what you mean by the auto amp. I am guessing you mean the fan blower control unit amplifier or resistor, depending upon the type of system you have. Again though, your system seems to work properly, its just that after 1.5 to 2 hours driving in certain heat conditions your evaporator is most likely freezing over.
I was just reading a bmw thread about the same thing, though for that poster it occurs after roughly 3 hours. Seems like if you have the cool setting at too low a temp and the fan going at a low speed this happens. I would experiment with setting the cabin temp a bit higher ( not on lowest setting on hottest day) and keeping the fan speed on a higher setting. Also noticed you are in Australia. Have you checked the Aussie X trail forum? Maybe someone there has more experience with the issue?
These days in Canada keeping the cabin warm is more of an issue that cooling it down lol.
 

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..ok
im not in Aus ...I'm in the Philippines.
a/c auto amp is what Nissan call the control unit..the bit with the dials on it.
the fan speed is never low ..its always over half way ...often max.
i have searched all x trail forums known to me for another similar fault ..this is the only thread I found.
the temp setting that I select cannot be 'too low' to cause these symptoms..I set temp. and the system tries to cool down the cabin best it can.
As I said before tho .... if it is working correctly, it should NEVER freeze up the evap ...because there is a control loop in place to prevent that. The auto amp with input from evap sensor should cycle the compressor clutch to maintain evap temp LOW...but NOT near freezing. That's how it should work ...but I suspect that control loop is failing after 1.5hrs or so.
So ... either of those 2 items has an issue ...measuring & testing is difficult..because the fault condition doesnt arise until after 1.5 hrs of operation ...so..I am left with inspecting components to see what I can find. I have a replacement evap sensor..but they are a pain to replace. So firstly I shall remove the a/c auto amp and have a good look at it ...maybe run an iron over everything....
 

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..im all over the Aussie X Trail forum too .... read that thread before .... as I said..only time I've seen this particular problem mentioned has been on this forum .... be great to hear of a 3rd T31 with this issue but seems not...
 

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Well I hope you can figure it out. You seem to know a lot more about the functioning of the system than I do. Good luck with it.
 

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well...its taken a while to diagnose this fault.... given it needs 1.5hrs or so of operation to show its face...but I'm now as certain as I can be that a freezing evaporator is the cause. Twice now i have been driving the prerequisite 1.5hrs and the fault has appeared ..ie. the airflow from the vents has reduced significantly to the point where the aircon cannot keep the cabin cool. Both times this has happened the blower can still be heard running at full speed...just no airflow..or very little.

So ... each time it's happened ....i have turned off the aircon manually using the centre button on the fan dial ...but kept all other settings the same. Within 2/3 minutes ..the airflow was restored to normal and the cabin cools down again.

This can only be because of a frozen evaporator ... that defrosts ... once the compressor is disabled.

All I need to do now...is figure out which component is failing at the 1.5hr point ..its either the evap temp sensor ( cheap, but difficult to replace) ...or the auto amp ( expensive, but easy to replace!) .

Having bought a replacement evap sensor already..and compared its readings with the existing one... I'm .pretty confident that its not that. Which leaves the main auto amp ( aircon control unit). Unfortunately..they are 300+ $$ to buy new .. and there are several different variants. Mine is a lhd version (fan on left) ... and its a 27500 JG44A ... which is rare as hens teeth!!

I would just buy another ebay lhd version for about £90..but the plug(s) are different ...virtually all other versions have 1 large rectangular plug on the rear ... but mine has 2 smaller ones side by side! ...

So..until I find a replacement on ebay at a decent price ... Im kinda stuck with the problem. At least I now know how to defrost the evap quickly while on the move tho..thank goodness..
 

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Glad you have it figured out. I am not convinced changing either the sensor or the control unit will make a difference. It might just be that you are pushing the systems performance limits. Kind of like how some in Canada complain about the car being slow to heat when the temperature outside is -20 or below.
 

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i dont believe the symptoms are those of an aircon system reaching its limits.

Fact is that the fan is going full ..but there is little airflow from the vents ...which must mean an obstruction of some sort. Given that there is only the filter & evaporator between fan and vent ...it must be one if them causing it. It isnt the filter ..i had the symptoms while it was removed temporarily. Which only leaves the evaporator.
As further proof, 3mins after disengaging the compressor the airflow is back to full strength again .... that really can only be as a result of the evaporator defrosting - nothing else changes.

I had the back off the control unit... with a view to running a soldering iron over everything just in case a dry joint was causing all this. Sadly..the pcb looks a multi layer affair with a high concentration of surface mount components ..in short, its not the sort of board that will take too kindly to a hand held iron ...
So ... looking to replace..if poss..at reasonable cost of course.
 

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I have a dehumidifier that is low on freon and it freezes half way to the serpentine.
My home ac was low on freon and it couldn't generate all the heat it was suppose to do. The serpentine outside had frost only 8cm high.
After a check up and a fill everything now is back to normal.

Have you checked both switches, high and low?
 

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i have had the refridgerant level checked and yes, it was fine ... I have not checked the operation of any high & low switches so I may do that ..thanks.
Remember tho ..the system operates perfectly for 1.5 - 2hrs ... and can be 'fixed' by manually de-clutching the compressor for a few mins. I'm not sure a switch issue would cause the system to react like this... but I will certainly check them.
 

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I have similar problem but the air con goes off after about five seconds. Fans work, ac works just doesn't blow. Garage says everything working fine, fluid levels okay. Real pain as it is still under warranty. Can only get ac by turning off and back on using the console and then only get a two second blast.
 

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If the fan and compressor are still spinning then it sounds like your airflow is obstructed. Three possibilities to check, a clogged cabin filter, debris in the cowl blocking the intake, or a blocked evap drain hose that's "drowning" the evaporator.
 
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