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-   -   Strange issue: AC stops cooling above 50 kmph (https://www.team-bhp.com/forum/technical-stuff/274033-strange-issue-ac-stops-cooling-above-50-kmph.html)

Hello members

I am writing this post on behalf of my friend who is facing a strange and irritating issue with his Duster.
The model in concern is the 85ps 2015 (old model).

The issue that my friend faces is regarding the air conditioning system in his car.
The AC works fine with the compressor engaged at idle and while driving at speeds of up to 50 kmph , at any higher speed the compressor would cut off and ac stops cooling completely left only with the blower .

Have visited multiple workshops and no one has an explanation for this occurrence.
During the last visit the compressor was serviced, still no change in the situation.

Key points

1) AC works fine at idle and speeds upto 50 kmph
2) At speeds over 50 kmph the compressor cuts off , left only with blower running
3) Rpm does not play a role in this , compressor works fine even at 50 kmph in second gear
4) Compressor restarts when we slow down from a higher speed to less than 50 kmph
5) AC output is very good once the compressor works
6) No increase in engine temperature above optimum , electric fan works fine

Can anybody give your valuable opinion regarding this strange and irritating issue?

Thank you.

I would:

1. Check the cooling fan in the engine bay
2. Check the refrigerant pressure, both high and low
3. Wash the radiator + condenser externally
4. Check if the compressor clutch operation is fine
5. Check if the cooling coil is clean, and if icing is happening there

AC compressors often cut out when the car begins to overheat, without the temperature needle actually climbing up noticeably (choked radiator + condenser). Or the cooling coil inside the dashboard is dirty and tends to ice up quickly, cutting out the compressor.

The compressor is not likely to cut out exactly when 50 km/h is reached, but a minute or two after running at that speed. Please confirm.

Indeed a very puzzling issue, why don't they disconnect the speedo sensor and see what happens. If this is related to speed the only input is from speed sensor right?

Since RPM is not related to the issue, compressor was serviced and gas also topped up during this?

Check the belt tension of the belt driving the AC compressor. As the engine RPM goes beyond a limit, the belt seems to be slipping. In lower gears, the vehicle rpm does not go above this slipping rpm long enough to be able to feel this, but above 50 kph, the rpm might be consistently above the slippage rpm to be able to feel it.

If the issue is related with engine RPM, apart from the belt tension check if the system has excess refrigerant, with which the compressor can't handle the pressure after certain rpm (discharge rate)

How long was this combination tried?

It is a strange issue. There are a couple of things why an AC could be influenced by speed. The most likely one is that at speed a larger volume of air is pushed through the system, requiring higher cooling capacity. If the system is relatively low on refrigerant it might stop. Alternatively, a clogged condenser or evaporator can cause icing, which also results in no cooling.

The items mentioned by SS travellers must be checked. Low refrigerant is a real possibility. With the engine idling it might work fine, but higher air flows might cause the problems.

An indication might be how quickly the compressor is cycling on/off. On car AC every 10-20 seconds is not unusual, but anything more often is an indication of the system being low on refrigerant. Try the system with the engine running at idle and the blower fan on max for a couple of minutes. Keep the doors open to allow maximum airflow. If the AC stops, you have found the cause!

Do get the pressure readings taken too. Another suspect could be a wonky expansion valve.

Good luck, let us know what you find.

Jeroen

Temperature needle is actually based on a temperature range instead of a static number. For example in my Honda Civic temperature gauge stays at mid level between 88 - 105. So the might actually be getting overheated but not showing on the gauge. In my case the AC used to get cut off the moment temperature hit 105 mark and that will bring the tem Down to 88. Because of which the temperature needle never moved. My mechanic bypassed the temperature sensor and I ended up with a blown head gasket.

I too never had the issue when the car was stationary. The only way to check this is to connect an OBD to the car and monitor at what temperature the AC is cutting off.

1) Cooling fan works fine confirmed by one of the mechanics
2) Checked
3) Cleaned
4) First thing was the compressor clutch replacement
5) Yes serviced

Regarding the 50kmph speed:

This factor was found out by us during a long trip.
There was no specific pattern for the compressor working to be identified . It took us almost a month to identify this speed factor.

At first we thought that compressor would not cut off if given light acceleration - proved to be false.

Now the situation is like whatever maybe the engine rpm ( tried decelerating from 65 to 50 in every possible gear- so different rpm bands) , the moment the car goes under 50 kmph the compressor kicks in and cools the cabin.

Yes a very puzzling issue indeed:coldsweat

Will try our luck with the speedo sensor next time.

Yes the compressor was serviced and gas topped up.
The AC works perfectly under this speed limit.

Checked the belt tension, it was fine

The compressor works fine even in second gear at 50 kmph or even in first gear at 4000 rpm ( don't remember the speed of the vehicle at that time )

Yes the compressor was serviced and the refrigerant filled correctly.

We have tried this for atleast two month's and this works every time.
The moment you go below 50 regardless of the engine RPM the compressor kicks in and cools the cabin

Thanks , will try it out

There is also another thing that I have not mentioned about the car.

The engine attains a particular temperature(according to the gauge) and stabilises there even if driven hard , like all other engines. In case of duster , I think it is 4 bars.

But in case of this engine, the temperature reading actually goes down two bars ( according to the temperature gauge) if the car is driven with a light foot.

I have not seen the temperature gauge of a car dropping after it reaches the optimum temperature.
This is happening in 34 degree celsius Kerala roads

Suggest that your friend gets an OBD-II scan done from Renault (even if there is no CEL).

I would suggest getting the speed sensor and the Coolant Temperature Sensor checked. If these things get crossed out, try swapping the ECU out with another one.
Does the car have Automatic Climate control?

Mod note: Back to back posts, please use Multi Quote [Quote+] or EDIT after the post is approved. Thanks.

Will try , thanks :)

Ok I will ask him to get those checked.

The last mechanic said that it could be an ECM related issue.
My friend is actually tired of every mechanic doing the trial and error method in his car.

No the car does not have ACC , it's the manual one.

Is there any other sensor that could be the culprit?
I really think that this is a minor sensor issue that every other mechanic is overlooking.

Goto Nissan, ask them to do a scan and look at the logs. If needed drive with analyser and see if anything is being recorded after the 50 kmph cut off speed. If it is speed related it has to be speed sensor. Whatever it is, from the looks of it, seems to be a sensor or an ecu related trigger.

Will try that out from the dealership service centre.
The only thing that prevents him from going to the company is that they asked him to replace the whole compressor at first visit.

They couldn't even find a pattern of occurrence.

I am facing a similar issue in my 2010 Beat. My car had an engine overhaul a month ago and I have been facing a similar problem ever since. My car's AC works fine when the car is running but when the car comes to a stop and is at idle, the compressor either turns off completely or does this cut off -on thing for a second or two. Only the blower works when the car is at idle. My car's ECM was recalibrated and this issue has been there after the engine overhaul. I need to take my car to my mechanic or some AC specialist, as this issue is irritating I must say. My car has the auto AC function, and not a manual unit like the one on the OP's car.

Very weird issue indeed. Two things come to my mind.
1. The fan is working in the reverse direction. During stand still it will work. I’m thinking beyond 50kmph there is no air circulating through the radiator. Ideally it should heat up the engine too.. but this is a remote chance to rule out.
2. Icing in the lines due to a faulty sensor. When the AC stops working check the lines and possibly (?) the evaporator coil for icing