AC on when switched off?

[m666 edd]

Driving home from work today and I thought I felt a bit cold, put my hands over the vents and the air was very cold. CC was set to 20 as always (fans on auto and not blowing that very hard) but it felt like the AC was on. It clearly said AC off though.

Put it up to 22 and it didn't really seem to make a difference. When I got home I saw that the outside temp was 16 so it couldn't have just been the ambient temps causing that much cold.

Thinking back I also tried turning the AC on and off while driving and didn't notice the noise it normally makes and the change in running note.

Got home quite late so it was soon dark and haven't checked anything out like fuses etc yet. Has anyone had this happen to them? CCU board or relay maybe?

[Hagasan]

Driving home from work today and I thought I felt a bit cold, put my hands over the vents and the air was very cold. CC was set to 20 as always (fans on auto and not blowing that very hard) but it felt like the AC was on. It clearly said AC off though.

Put it up to 22 and it didn't really seem to make a difference. When I got home I saw that the outside temp was 16 so it couldn't have just been the ambient temps causing that much cold.

Thinking back I also tried turning the AC on and off while driving and didn't notice the noise it normally makes and the change in running note.

Got home quite late so it was soon dark and haven't checked anything out like fuses etc yet. Has anyone had this happen to them? CCU board or relay maybe?


Hi Ed,

just look down at the ac compressor and see if the clutch is engaging and running the pump...

Gary

[Kaz-kzukNA1]

Hi, m666 edd.

Always setting the dial at 20degC sounds like you already have some problem but I know the performance of your NSX and may be you need to keep the cabin cold while you are driving….


Control of A/C On and Off depends on the input from several sensors including the sunlight.


If you selected the ‘A/C OFF’ mode manually, it should stay like that.

However, it is not the same case for selecting the ‘A/C ON’ mode manually.

The A/C could be in OFF status if the evaporator temperature was very low.


If you think the A/C was ON continuously, then it sounds like you have CCU board failure as I have seen similar issue in the past.

In fact, sometimes, the A/C stayed ON even the CCU was completely switched off.


Also, you may have air trapped inside the heater core resulting in not getting warm/hot air.


Quite common if the coolant system was not bled properly.


To start with, please try the CCU self diagnosis test as well as the Function & Operation check based on the attached pdf files.

9225

9226


Function & Operation check is very useful as it will force the CCU to ignore the sensor input and controls the fan motor speed, air outlet mode, compressor clutch switch, air temperature, etc based on the check mode.


You can easily tell whether your A/C is continuously in ON status or not by the above check.

It will cycle through A/C On - Off mode during the check.

You can place your hand in the open air space between the forward section of the front R & L tyre and the plastic inner trim inside the wheel arch.

The ribbed plastic trim is actually the outlet of condenser fan for the A/C system.


If you don’t feel any air when the A/C is ON, the fuse is blown or you have other problem.


On our NSX, there are R & L condenser fans and due to the spike current, NSX is famous to blow one or both of the condenser fan fuse inside the pentagonal fuse box under the bonnet.

If you can feel the strong air from the condenser fan even when the A/C is OFF, you have a problem as condenser fan should only operate when the A/C is ON.





A/C is ‘Air Conditioner’ and not ‘Cooler’ so the air temperature can be controlled by the CCU temperature dial.


Based on the dial setup and several sensor inputs, CCU will adjust the amount of hot coolant passing through the heater core and the position of the (cold/hot) air mix damper that will decide the air temperature blowing into the cabin.

Again, you can monitor the movement of these during the Function & Operation check.


It is best to crack open the heater core bleeder plug to check for any air in there but you can do a quick check before that.

Please visit the following post.

http://www.nsxcb.co.uk/showthread.php?5940-CCU-Computer-board-Service-Part-1-3&p=54812#post54812

While the engine is cold, please set your CCU dial at 18degC. You can set your fan speed to MIN to minimise the fan noise. Rest of the setting doesn’t matter.

Start the engine and once the engine has warmed up, try to touch the ‘Hot water return passage’ as seen in the 1st photo. It’s the silver aluminium pipe.

You should be able to keep touching it as there should be no hot coolant passing through there but in case of system failure, please be careful as it could be hot.

Keep running the engine and now set the CCU dial to 32degC. Immediately, you should feel hot coolant at the same pipe. If you can keep touching it for more than 10sec, you are very likely to have air in the heater core.


Depending on the year model, you will see threaded bleeder plug at the same pipe as in the photo or on the earlier models, it is a simple black rubber cap held by the hose clamp at the same location.


Just open it slightly and VERY SLOWLY when the engine is cold until you see continuous stream of coolant.

If the coolant system is under pressure, it could shoot up the coolant in the air so you must try to open the bleeder/rubber cap super slowly.

Place plenty of shop towel under the bleeder as you don’t want the coolant to sit inside the battery holder case for many years. Having said this, you can always wash off the spillage with plenty of water.

Good luck and if you need your CCU board serviced, just send me an email through the drop down menu by clicking on my user name after you have logged in.

Kaz

[m666 edd]

Hi Ed,

just look down at the ac compressor and see if the clutch is engaging and running the pump...

Gary

I should have done this at the time but I'm certain it was running. The last few journeys I've done since the AC has been working correctly - off when it should be and engaging the clutch when turned on etc.


Thanks for the detailed response Kaz. I didn't realise the CCU has a self diagnosis & function and operation check.

My father knows a lot regarding electronics and has repaired and replaced many capacitors on various circuit boards so servicing the CCU shouldn't be a problem. I'll try diagnosis and function and operation check first.

Thanks again.

Ed