C4 1.6 hdi 2008 AC fault

This is the Forum for all your Citroen Technical Questions, Problems or Advice.

Moderator: RichardW

Tonyl
Posts: 21
Joined: 09 Jun 2022, 12:41
x 7

C4 1.6 hdi 2008 AC fault

Post by Tonyl »

Hi

I recently did some engine work that entailed engine out. As a result, AC was pumped down, pipes disconnected, compressor off etc. Before work AC worked.

Since putting all back and having system recharged it doesn’t work. I’ve used diagbox which throws up code F995 - Engine Fusebox - fault in the aircon compressor - ownership not referenced. I’ve double checked all plugs are back as they should be. As I cannot find anything on line re this specific fault - anyone any ideas what to look at? It worked before!
wheeler
Posts: 5801
Joined: 21 Sep 2002, 19:07
x 428

Re: C4 1.6 hdi 2008 AC fault

Post by wheeler »

Is there power going to the A/C compressor? does the clutch engage if you apply direct power to it?
Tonyl
Posts: 21
Joined: 09 Jun 2022, 12:41
x 7

Re: C4 1.6 hdi 2008 AC fault

Post by Tonyl »

Yes - I actuated the clutch via diagbox and I can hear it clicking in. That function is blocked however when running.
ozvtr
Posts: 205
Joined: 13 Oct 2020, 01:11
x 58

Re: C4 1.6 hdi 2008 AC fault

Post by ozvtr »

How many electrical plugs are on the compressor? Is there one black plug on the back of the compressor?
F995 seems to relate to the variable displacement modulator valve. If the compressor has this connector, is it pushed all the way home? Can you check the resistance of the valve? Can you put a load (light bulb) across the loom connector and see if that changes anything?
Tonyl
Posts: 21
Joined: 09 Jun 2022, 12:41
x 7

Re: C4 1.6 hdi 2008 AC fault

Post by Tonyl »

Thanks for coming back. There are two plugs - yellow and black - one to the clutch and one to « something else ». I was wondering if that’s the low pressure switch which I understood is integral on some compressors. As it’s a clutched unit I had assumed no variable delivery valve on this one. I will double check connection tomorrow.
ozvtr
Posts: 205
Joined: 13 Oct 2020, 01:11
x 58

Re: C4 1.6 hdi 2008 AC fault

Post by ozvtr »

Tonyl wrote:
18 Jun 2022, 17:06
Thanks for coming back. There are two plugs - yellow and black - one to the clutch and one to « something else ». I was wondering if that’s the low pressure switch which I understood is integral on some compressors.
No and no. LOL(no offence)! The pressure 'switch' is in the "high side" vapor line. And its not a switch, it's an analog sensor. Its used by the engine ECU to detect if there is enough gas (pressure) in the system and how much of a load the system is under. On hot days the heat load will push the high side pressure up. The engine ECU then uses this information to drive the radiator cooling fan faster or slower. Or if there is not enough gas the engine ECU wont engage the clutch. Yes, when the engine is not running, LEXIA will let you test the clutch irrespective of whether the system is 'working' or not.
I am not a LEXIA guru and have not found if you can monitor the high side pressure.
Tonyl wrote:
18 Jun 2022, 17:06
As it’s a clutched unit I had assumed no variable delivery valve on this one. I will double check connection tomorrow.
All of the compressors PSA have used since about 2000 are variable displacement. There are 3 types. Mechanical and two types of electro-mechanical. The mechanical type have a counter weight that varies the displacement in proportion to the speed of the compressor, effectively outputting the same volume at low or high speeds. The electro-mechanical types vary the displacement via a control valve on the back of the compressor. They either do or don't have a clutch. It's the later compressors that don't tend to have a clutch.

It looks like the BSM is not able to run the modulator valve in the compressor. Faults could be in the BSM, the wiring from the BSM to the compressor or the modulator valve in the compressor. Theoretically nothing should be broken!? But co-incidental failures do happen!
Tonyl
Posts: 21
Joined: 09 Jun 2022, 12:41
x 7

Re: C4 1.6 hdi 2008 AC fault

Post by Tonyl »

It comes to mind I did not seal the condenser/drier pack whilst it was disconnected. Is it then possible it’s saturated and preventing any gas flow? I’m not an AC guru at all!
ozvtr
Posts: 205
Joined: 13 Oct 2020, 01:11
x 58

Re: C4 1.6 hdi 2008 AC fault

Post by ozvtr »

Tonyl wrote:
20 Jun 2022, 01:16
It comes to mind I did not seal the condenser/drier pack whilst it was disconnected. Is it then possible it’s saturated and preventing any gas flow? I’m not an AC guru at all!
Not really. The descant pack wont swell. It will absorb some moisture out of the atmosphere, but it depends on the humidity of the air. This would not stop the system from running but may cause long term damage...may. You would need to get a lot of things wrong for that to happen.
If there was a blockage, the static pressure of the system would still allow the compressor to kick in. After that, the system may or may not shut down. Depends where the the blockage was. A blockage at the receiver/dryer would cause low pressure at the high side pressure sensor and the system would shut down. Eventually, the pressure on either side of the compressor would equalize and the system would start up again.
Remember, the car has thrown a code and that may be what is causing the system not to run. It has detected something is wrong and refuses it to allow to run.

Given all the information, your problem seems to me to be with the modulator valve or the wiring or the BSM. That seems to be what the code is complaining about. Having said that, I am not sure that loss of the modulator valve should cause any harm to the system and warrant the relevant ECU to shut the system down. When you find out, we'll have the answer. :-D
Tonyl
Posts: 21
Joined: 09 Jun 2022, 12:41
x 7

Re: C4 1.6 hdi 2008 AC fault

Post by Tonyl »

Ok, I have V and earth at the compressor modulator valve feed so this seems fine. I decided to go back to Diagbox and dig deeper with throws up that compressor is blocked due low pressure trigger. I’m starting to wonder if my friendly local garage that said they’d filled the system actually did at all. So before I start delving deeper I will head to another to check if there’s actually gas in it!! You will see from pics there is intermittent start signal which I think is start block due low pressure kicking in but thoughts welcome.
Attachments
0C523CE5-C298-4CCF-881D-0D9769249203.jpeg
FE9DE2A4-590E-4E33-BA4C-9607EF781744.jpeg
8574AB5A-0E7B-47A8-BA10-399A096D076D.jpeg
7E436D05-141E-4565-86D7-2C49F39F5AD8.jpeg
7FD8F060-AA32-472D-AC69-6E620E111264.jpeg
AE0E098C-2159-4FD6-8A65-58D2153315B7.jpeg
Tonyl
Posts: 21
Joined: 09 Jun 2022, 12:41
x 7

Re: C4 1.6 hdi 2008 AC fault

Post by Tonyl »

….and low pressure safety showing as active.
RichardW
Forum Treasurer
Posts: 9919
Joined: 07 Aug 2002, 17:12
x 564

Re: C4 1.6 hdi 2008 AC fault

Post by RichardW »

Yeah, it's either got no gas in it or the pressure switch / wiring is faulty.
ozvtr
Posts: 205
Joined: 13 Oct 2020, 01:11
x 58

Re: C4 1.6 hdi 2008 AC fault

Post by ozvtr »

Where has the F995 code gone?
When did the P0532 code popup?
Hard to diagnose things with DUFF GEN.
Yes...what RichardW said!
Tonyl
Posts: 21
Joined: 09 Jun 2022, 12:41
x 7

Re: C4 1.6 hdi 2008 AC fault

Post by Tonyl »

DUFF GEN? What does that mean?

That code just came up. I clear codes to see what comes back and then focus on those.