I own a 2008 Skoda Fabia, and recently I've been experiencing an issue with the AC. It cools fine for about 30 minutes, but then the cooling stops, although the fan keeps blowing air. To get it working again, I have to turn the car off and on. 

 

I visited a local AC technician who thought the issue was with the compressor wall, the high-pressure switch, and the water pump (since he noticed the engine was running hot). I replaced all of these parts, but the problem persisted. While replacing the compressor wall, I noticed a black oil-like substance leaking from the compressor. However, the technician assured me that if the compressor or condenser were the problem, the cooling wouldn't work at all, not even for the first 30 minutes. We also tried removing and reinserting the same evap sensor below the steering wheel and noticed that the pipes were getting frozen when removed and the ice melted when inserted. 

 

I then took the car to a different technician, who tested the power supply to the compressor by attaching a light bulb to the compressor wire. After about 30 minutes, the light went out, indicating the power was being cut off. When the car was restarted, the light and the AC came back on. He was certain that the issue was electrical, not with the compressor or the AC system itself, since the cooling would restart once the power was restored.

 

We scanned the car, and the only error that came up was related to the drive battery voltage ("implausible signal"), which the technician said wasn’t related to the AC issue. He ran tests on various car modules, and while checking, the wipers activated randomly, and the AC started cooling again, only to stop after 30 minutes as usual. Despite the tests, no significant errors appeared, except for the battery voltage issue. 

 

The technician now believes the problem lies with the Body Control Module (BCM) and suggests it needs replacing. I'm unsure if this is the real issue, especially since I initially thought the black oil in the compressor indicated a fault with the compressor or condenser. Could it be the BCM, or is there another potential cause? I’d appreciate any advice. Please help. Thanks

Edited 25 September, 20241 yr by Zaid

The aircon compressor is commanded by the AC control module not the body control module.

 

You need to interrogate the AC control module using VCDS or similar, when the AC stops it should show a compressor shut down code in measuring blocks, if it is showing the compressor still being commanded then its a wiring problem or a faulty modulating valve.

 

My guess is that the shut down code will be for de-icing of the expansion nozzle the blockage having caused the high side pressure to shoot up, this will be due to water vapour in the refrigerant gas probably through not vacuuming down the system for the required 30 minutes before refilling.

 

PAG oil should be green and I have never seen anything but virgin green non contaminated oil when stripping down a compressor, if the PAG oil is contaminated then the expansion valve might be clogged with schmoo.

As I often make mistakes regarding the Fabia through assuming that it has the same systems and equipment as other vehicles then someone like @Breezy_Pete may correct what I have written regarding the AC control module and the compressor modulating valve, from your description of the test light it sounds like you may have a clutch controlled compressor.

Thank you so much JR for your post, my car has a wall controlled compressor and not a clutch controlled compressor. 
 

i dont know how to set up the vcds myself and my technician in India has a tablet with which he scans my car. 
 

 

my car has a climate control module that states no errors found. However i couldnt find the AC control module. 
 

if you suspect a clogged expansion valve, how do we explain power cutting off to compressor and bulb going off (bulb connected to compressor wire to test power)? Please help. Thanks

The climate control module will have the 'shutoff code' available to be read by an appropriate scan tool, if it is connected at a time when the A/C is not cooling, I think. 

Lots of info here: Tis’ the HVAC Season | Ross-Tech Forums

Thanks @Breezy_Pete, do you think i can set up vcds and study it on my own? Can i fix this on my own? I don’t have much knowledge regarding low pressure and high pressure and gas, etc. I’m not getting a technician good enough to do this. Please help. Thanks

VCDS Lite, the freeware version should work on your car. Download it via ross-tech.com website.

 

You then need a (cheap, generic) KKL/FTDI cable to connect laptop and car together.

 

Okay i can connect the kkl cable to the free version of vcds. And then run a scan before the compressor cutting off and after it cuts off, if the compressor

 says shut off it is wiring problem it it doesn’t says **** off it is compressor problem. Am i right? Sorry for explaining it in a noob way. Thanks

No, you don't run scans, you just connect to module 08 (HVAC) and look at measuring block data, live.

One channel of this will be "Comprossor shut off code"

(With that spelling error in compressor, if I remember right).

 

 

Okay ill get back to to you with what it says. Thanks

Ps -just curious what is a better problem, if they compressor does shut off or nah? 
Thanks 

The shut off code tells you why the compressor has been disabled, assuming this is what happens after 30 minutes running.

That information should be very helpful in fixing it. Codes are in that link to Ross-tech forums that I gave earlier.

Measuring value group 2, field 1 is apparently where the shut off code is found.

Okay thanks a lot @Breezy_Pete. I’m going to get started on getting you the info. Thanks

I’ve ordered a kkl cable which will take 7 days to arrive. Turns out it is not very easily available in India. I will look for local shops as well tomorrow. Just curious if this device will work too - https://amzn.in/d/a5LgFbW - looked interesting. Let me know. Thanks

Edited 25 September, 20241 yr by Zaid

Hey @Breezy_Pete, it will still take a week for my generic kkl cable vag com to arrive from china. 
 

meanwhile I took my car to the authorised dealership to run some test and this is the test that came out, i have attached it with this post. 
 

i have also attached the before cooling goes off and after cooling goes off low and high pressure on the manifold. Have a look. Thanks

What was the ambient temperature when the manifold set readings were taken?

 

You say your compressor does not have a clutch and that it is "wall" controlled, this is an error in translation, do you mean the modulating valve?

 

You say you have replaced the high pressure switch, if you have a non clutch compressor there is no high pressure switch, there is a pressure transducer and the aforementioned modulating valve, what exactly did you replace? from the mention of the contaminated refrigerant it sounds like the modulating valve.

Re the guage readings, the compressor has not shut off on the second photo, it is running at reduced output to maintain the set temperature already reached, if it was not pumping the high side reading would have reduced and the low side increased with them both equalising at the system gas pressure which is dependant on the ambient temperature.

 

When pumping refrigerant the high side rises and the low side drops.

 

I mean i changed the high pressure valve. Sorry my bad. 
The high pressure switch is what I was told. I’ll attach a pic of things i changed. Have a look. 
 

yes you are right the second photo of the manifold was immediately clicked as soon as the cooling stopped(you couldn’t feel the car getting warm yet, it will take some time) if i waited further in sure the compressor wouldn’t start again and the gauge reading would change.

 

Pressure transducer on the left, can be changed without depressurising the system.

 

Modulating valve on the right, refrigerant must be recovered or lost to replace.

 

The compressor is running in the second photo but at a lower output which probably means the modulating valve is doing its job, this would normally happen when the cabin temperature has reached the set point from the rotary control on a Climatic system or the LED temp indication on a Climatronic system. The pump does enough work to maintain the temperature and no more.

 

What temperature did you have the AC set to when it cuts out after 30 minutes and what was the ambient temperature.

Yes I’m aware of the systems of replacing the left component with a pressurised system and the right thing needs to be replaced with removing the refrigerant and charging it again. 
 

The temperature of the surrounding was 28-29 degrees centigrade. Could it be a wiring issue or the power switch to the compressor malfunction. When i search for the error 00898, it shows videos of the switch.

42 minutes ago, Zaid said:

When i search for the error 00898,

 

You made no mention of this.

 

On 25/09/2024 at 10:58, Zaid said:

We scanned the car, and the only error that came up was related to the drive battery voltage ("implausible signal")

 

Actually the 00898 error popped up today on the official authorised dealership scanner. I have attached a pic of the scan. I thought you noticed it. Sorry

Okay so now there is another update. I have changed the expansion valve, condenser, and compressor since this system was contaminated. But unfortunately, the ac still shuts cooling after 45 minutes. This is super annoying, no electrical fault reported in scan, ac system completely flushed and replaced. Ugh!

Probably because the fans are not cutting in properly and the system is overheating after 45 minutes running. Stop staring at the computer and fix the fans!

The fans are spinning at low and high speed. Atleast thats what it looks. Immediately switching off and igniting the car again starts the AC cooling. If the car was heating- the AC wouldn’t start almost immediately after it was switched off and switched on, right?

Hey @Breezy_Pete, I got my kkl cable and I got an opportunity to test the shut down code on my car as suggested by you. Turns out I’m getting shut down code 12. Both the stage fans are being switched on as well. How do i proceed with diagnosis from here. Please help me. 
I also noticed that the outside temperature sensor that comes in the left part of the bumper has been cut off die to rat bite (I’m going to fix it - can that be an issue as well), Also when the car is being driven I’m getting an internal control module error. I’ve attached the images of the scan. The other errors like high pressure sensor error, etc were cleared upon clearing the codes however the internal control module error continues to pop up even after clearing after driving the car a bit. - https://www.transfernow.net/dl/20241017cnoRMwgo