Air Con prob...well i think!!! [Archive]

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rtbm

31-08-2009, 04:11 PM

Sudesh

31-08-2009, 04:24 PM

NSXGB

31-08-2009, 04:25 PM

http://www.nsxprime.com/FAQ/DIY/climate_control.htm

Try this CCU test, see if it throws anything up.

Could possibly be a number of things.
CCU capacitors gone bad is a common one, if you've never had it fixed, send it to Kaz anyway to be done, it will go eventually and you need to repair it before it's too bad. A bunged up aspirator fan in the centre console I think could also cause you problems if bad.

HTH

Kaz-kzukNA1

02-09-2009, 10:20 PM

Hi guys

Air con used this week for the first time in a while.....great brit summer!!!....all nice and cold...and turn up heater nice and hot....prob seems to be the regulation in between is'nt reflecting temp on display...i,e set it to 22 degrees still very cold.....set to 27 degrees luke warm and so on....is the fault with windscreen sensor or the one in the centre console...or is this just air con on a 1991...18 yr old car!!!.

regards

russell

Hi, Russell.

The temperature of the air is controlled by the 'water valve' in the front compartment under the bonnet. Please have a look at the photos in post #18 of the following link.

http://www.nsxcb.co.uk/testvb/showthread.php?t=5940

Around this time of the year, you may not get max hot air (water valve lever all the way towards the bulkhead) unless you set it to 32degC. As soon as you set it to 31 or 30degC, the water valve may move to mid position resulting in mild air.

There are many inputs and outputs related to the actual air temperature and there are at least 5 sensors involved for the control so it is not easy to test the air temperature by just turning the temperature dial.

The best way is to use the Function & Operation check procedure as in NSXGB's post. I'll also attach the pdf version for you.
This procedure will force the CCU to ignore the sensor input and send out the certain signal to each actuator and motor to check their function. During this procedure, please have a look at the water valve and you should see it moving in 3 different position (all the way towards the bulkhead, half way, all the way towards the front bumper).

While you are there, try to hold one of the silver pipe at the water valve. When the engine is warmed up and if you can hold the pipe when the water valve is all the way towards the bulkhead, then you have some air trapped inside the heater core. You won't get max hot air if this is the case and I have seen many NSX running with this condition.

You can bleed the air from the heater core quite easily.

Self diag test will not tell you the sensor failure unless it is open or short circuit. As the temperature sensors used for the CCU are thermister, it's only a 2 wire sensor changing its resistance value depending on the temperature.
Therefore, even if it was sending out wrong resistor value, CCU won't be able to recognise the failure so please take this into consideration when carrying out the Self diag test.

If your CCU has never been serviced, I'm quite confident that you have several issues without being noticed.
As in NSXGB's post, please send it for the service (NSXGB, thank you for refering it to me).

Hope this will help.

Regards,
Kaz

rkanaga

21-09-2009, 02:05 PM

Hi Kaz, I have followed your very informative posts with great interest. i would echo the thanks that others have given for your great service!

May I ask you a question about a heater problem I am having?

I have a 91 NSX. It originally had a CCU problem which manifest itself by the mode control not working, and not being able to direct air to the windscreen vents.

I sent my CCU to BrianK in the US and he fixed a number of capacitor problems and some broken tracks.

That seemed to do the trick. However more recently I noticed curious problem as follows:

If you set a temperature when the car is running at speed, and then slow down in traffic, the air goes cold. If you rev the engine the air heats up as before (even if you are sitting with the car i neutral). I also have the problem you have talked about where the heater control does not seem to vary much unless you turn it right up to 32 degrees or so. I will make the checks to see if this is caused by air in the heater core as you suggest, but do you think that the problem of the air going cold in traffic has the same cause, or is it something else?

Many thanks

Robin

(PS pity you're not repairing speaker amps, as mine has just gone as well!)

WhyOne?

21-09-2009, 02:32 PM

Air con used this week for the first time in a while.....great brit summer!!!....

Sorry to hear about your potential problem Russell.

Just one recommendation from technically challenged me - it is a really good idea to run the a/c for 10 or 15 mins. every few days, Summer or Winter, whether you need it or not.

NSXGB

21-09-2009, 05:30 PM

(PS pity you're not repairing speaker amps, as mine has just gone as well!)

Kaz will fix those for you too if you ask nicely.

Kaz-kzukNA1

22-09-2009, 01:17 PM

....
I sent my CCU to BrianK in the US and he fixed a number of capacitor problems and some broken tracks.

That seemed to do the trick. However more recently I noticed curious problem as follows:

If you set a temperature when the car is running at speed, and then slow down in traffic, the air goes cold. If you rev the engine the air heats up as before (even if you are sitting with the car i neutral). I also have the problem you have talked about where the heater control does not seem to vary much unless you turn it right up to 32 degrees or so. I will make the checks to see if this is caused by air in the heater core as you suggest, but do you think that the problem of the air going cold in traffic has the same cause, or is it something else?
........

Hi, Robin.
This is the typical phenomenon when you trapped some air inside the heater core. Quite a lot of NSX are running under this condition. While you can easily bleed the air, it is important to know where the air came from. It is possible that the air was not bled thoroughly when you had your coolant replaced last time, small leakage somewhere in the system and so on.

I have attached the old photo from my other post of Air Con (A/C) ‘CCU Computer board Service’ below.
6225
Unlike other production car, the hot coolant from the engine will enter the radiator from the bottom and then exit from the top. Before entering the radiator, there is a branch on the hot coolant pipe under the bonnet. This is the black coolant hose connected to the ‘water valve’ in the photo and it is the inlet to the heater core. After passing the heater core, the hot coolant will be returned through the outlet hose and aluminium pipe.

The coolant is circulated through the system by the water pump which is driven by the timing belt.

So, regardless of the car speed, the water pump speed is determined by the engine rpm. Therefore, if you trapped lots of air in the heater core, you’ll only get small amount of hot coolant into the heater core when the rpm is high enough but then if you drop the rpm, there will be no more hot coolant into the core and eventually, it will be cooled down resulting in only cool/mild air out of the air vent even at high temperature setting.

You may not notice this if you set the CCU temperature other than 32degC as you are partially closing the water valve. If you already trapped the air in the heater core, then you don't have enough coolant flow through the heater core resulting in narrow band temperature control.

So, as you guessed, when the car is at high speed or if you rev up the engine even the car is stationary, the water pump will be working fast enough to push some amount of hot coolant into the heater core.
If you drop the engine rpm, the water pump slows down and thus, no more hot coolant into the heater core resulting in cooler air temperature.
This is what you experienced the other day.

You can do a quick check on this.

Set the CCU temperature to 32degC (fan speed, vent mode, A/C on-off, none of these matter for this test) and warm up the engine to the normal operating temperature.
After this, keep the engine in idle for about 5min.
Keep the engine running and now touch the aluminium pipe at the outlet of heater core.
6228
Be careful, it could be very-very hot. If you can grab it for more than 3 seconds like this photo, then you definitely have some air in the system or you have special heat resistant hand. Please do not get someone to rev the engine to check further while you are working at the front of the car. It’s dangerous.

As you can see in the photo, this aluminium pipe is one of the highest points in the coolant system and thus, accommodates the bleeding point.
If you have earlier model, the bleeder will be rubber cap with a cramp. The later model will have bleeder screw plug.
6227 6226

To bleed the air in the heater core, please keep the CCU temperature at 32degC throughout the following procedure.

First, let the engine to cool down. If you have never worked on the coolant system, please leave at least several hours or even overnight to completely cool down the engine.
Then, slowly loosen the header tank cap in the engine bay to release any remaining pressure in the system. Once again, it is very important to have the engine cooled down before removing this cap. You don’t want to see your coolant coming out of header tank like a volcano.

Then, tighten the cap otherwise the trapped air will be bled too quickly in the following step resulting in water paddle in your battery tray or stream of coolant very likely to be heading towards your face. You can't clean the battery tray with ease as the drain hole is not at the bottom and you don't want to taste the coolant...

Now it’s time to bleed the air in the heater core. Place paper towel or something to catch the coolant coming out of the bleeder.

For the rubber cap bleeder, remove the cramp and slowly lift the rubber cap. If you can’t lift it with ease, then first, just twist it several times before start lifting it.
Don’t remove it completely but instead, try to make a tiny opening of less than 1mm by tilting the rubber cap at the top of the small bleeder pipe.
You will hear the hissing sound of air coming out of bleeder.
Once you start seeing the coolant, wait for a few second and place back the rubber cap and the cramp.

For the screw plug bleeder, slowly loosen the screw and wait for the coolant to come out from the bleeder hole.
Once you start to see the coolant without any bubbles, tighten it by finger first and then torque it to 9.8Nm (1.0kgf).
Be careful not to over tighten it.
You are dealing with aluminium thread.

If the amount of trapped air in the heater core is small enough, you may be able to get rid of it by setting the CCU at 32degC and driving the car in 3rd gear for a while with occasionally revving the engine to high rpm in order to push out the air back to the header tank.
I normally use vacuum fill procedure when replacing the entire coolant but also use this driving process to make sure no air is left in the system.

If there is no air in the system, you will see only a small difference between the coolant level at the header tank when the engine is hot and cold.

If you want to bleed the air of coolant system completely without special equipemnt, then please follow the procedure described in the workshop manual which you can find on several places on the web.

......

(PS pity you're not repairing speaker amps, as mine has just gone as well!)

As NSXGB mentioned, I do offer the service for Bose amplifier.

However, I don't have enough spare IC which is not available as an aftermarket parts and because of this, I feel it is not fair to everyone and thus decided not to setup a thread like my other services such as CCU board and Health check.

If you can send me an email through this site or I'll reply back to your PM with my email address, then I can forward you the detail on this service.

Regards,
Kaz

rtbm

22-08-2010, 04:02 PM

Hi Guys....i just started back on here after long lay off.....thanks for advice on air-con.....

regards

russell