Citroen c3 2008 No AC detected by Lexia

[areid]

Hi there,
I have a 2008 Citroen C3 (HDi 1.4). Lately I've been having a problem with the AC. When the engine is cold I can start the AC and the compressor kicks in cycling (turning on/off) one or two times at most. The fan works as I get cold air in the cockpit. After that, the compressor won't start again. If I leave the AC on the fan will continue blowing air into the cockpit and eventually will start blowing hot air.
Sometimes, during a long trip, the compressor may kick in again one time and after turning off it won't kick in again.
I connected a Lexia 3 to the car to check for error codes, but Lexia was unable to detect an AC installed in the car. That is, Lexia goes through the full diagnostics and does not detect the AC unit present in the car. When attempting to connect to it manually, it says it was unable to start a dialogue with the ECU. All other functions are recognized by Lexia without a glitch. In fact, I was even able to change the car's rd4 radio configuration.
I've taken the car to my long-time mechanic and he says it may be a sensor (he does not have Lexia). I changed the temp sensor in the cockpit located under the radio and accessible through the passenger's foot space. No joy. Any help/ideas would be appreciated.

[wheeler]

Have you tried connecting with the engine running some older Citroen A/C systems only communicate with the engine running as the A/C only works with engine running.
Also depending on spec it may not even have an A/C ECU, on the older C3 you had A/C or the higher spec climate control with digital display, only the higher spec one actually had a control unit.

[areid]

Hi wheeler. Thanks for the quick reply. I indeed tried different configurations. Ignition off, ignition on, engine running AC off, engine running AC on. Nada.
My C3 does not have climate control, only AC. Lexia detects the existence of an AC ECU, at least that's what I think it does. But then simply says unable to start dialogue with the ECU. I can recheck and upload an image of the actual Lexia messages later.
If it didn't have an AC ECU then it would have said so?
Could it be that the the AC unit is not factory installed but rather was installed by the dealer?

[xantia_v6]

Go through the live data in the engine ECU looking for a parameter like AC Inhibit or something like that.

Also look for related parameters in the BSI live data.

[areid]

Hi xantia_v6. Thanks for the suggestion. I'm not very used to Lexia. How do I go about watching the live data on the engine and the BSI?

[PaulC5]

Chances are it just needs regassing unless it has already been done in the last few years.

[areid]

Hi PaulCS. it was regassed a few months back. Tested airtight condition and passed OK.

[ozvtr]

My C3 does not have climate control, only AC. Lexia detects the existence of an AC ECU, at least that's what I think it does. But then simply says unable to start dialogue with the ECU.

LEXIA uses the RPO number and the BSI configuration to tell it what ECU's should be in the car. You can also add and remove ECU's by manually configuring the BSI and other ECU's.
The other thing is the revision of LEXIA's hardware and software. Earlier revisions of LEXIA may not be able to read later revisions of the ECU's firmware.

You should be able to go into the engine ECU's top menu and see if the A/C is enabled or disabled.
Under "actuator tests" in the engine ECU, you should be able to engage and disengage the compressor clutch.

Have you tried scanning the A/C ECU while the A/C is actually working?

[ozvtr]

Also depending on spec it may not even have an A/C ECU, on the older C3 you had A/C or the higher spec climate control with digital display, only the higher spec one actually had a control unit.

Both auto and manual A/C have an ECU. The evaporator temp sensor for both is connected directly to the BSI. The A/C ECU in the A/C control panel communicates to the BSI over the area network and requests the evaporator temp (well actually the temperature of the AIR coming off the evaporator) . The BSi then adjusts the compressor duty cycle to get the evaporator to a particular temperature.
The manual A/C panel ECU just requests a fixed temperature for the evaporator dependent on the temp knob position.
The auto A/C panel ECU automatically varies the requested evaporator temp, dependent on the temp selected and the actual cabin temp.
This way the interface between the auto and manual A/C and the BSI is kept the same.

At least this is the way the 2003-2010 C3's A/C worked. Cant speak for other models.

[areid]

Hi oztvr, thanks for your help.

I searched for the info you mentioned and found that the A/C ECU is present and the A/C appears as Enabled or rather Present (vs absent).

I then tried the Actuator Tests available in the BSI Diagnosis:

All tests were executed correctly, but nothing happened. The first time I tried with the engine running and Lexia showed an error stating that the test failed because it wasn't possible. I then tried with the engine off and the tests were executed, but the compressor did not start. I also tried both heating resistors but no noise was heard. No actuator test related to the A/C unit had a response, although Lexia states that the test was completed. Just to make sure the tests were working I tried testing other actuators like doors and wipers, and they were executed OK.

Afterwards, I started the engine and the A/C and, although the compressor was not running I went to the live measurements screen and got this:

So the A/C appears to be working, at least from the BSI's point of view, although the compressor is not actually running. Finally, I reviewed the configuration of the A/C parameters and got this:

I'm surprised and really at a loss. The BSI detects the A/C ECU, runs the actuator tests OK but the unit itself does not work. Could it be a wiring problem, a blown fuse or a faulty sensor?

Thanks for the help.

[ozvtr]

Well this shows that there is nothing wrong from a control stand point.
So the alternative is a physical problem.
The suspects would be the BSI or BSM, (Sorry I don't have access to circuit diagrams for the "all CAN BUS" C3 so I'm not sure), the wiring, the clutch coil or the clutch adjustment.
The next test I would do is check for voltage at the connector of the compressor. If no voltage, it could be the BSI/BSM or the wiring.
If you do have voltage at the connector, this means it is either the clutch coil or the clutch adjustment.
At this point you could try hitting the compressor with mallet! With the A/C on and the engine running, tap the center of the clutch pulley with a rubber mallet (or the like) and see if it starts spinning. The clutch is adjusted in the factory with shims to get the correct gap. Over the years the clutch wears and may not be able to pull in.
Lastly it could be the clutch coil. Check for continuity using a multi meter. Check both ways (swap the leads over) as there may be a diode across the coil.

[areid]

Thanks for the help. I have a couple of days off this week and will try to get below the car and inspect the compressor.
If you tell me how, perhaps I can give you a hand getting the circuit diagrams for the car. Can they be accessed with Lexia?

[wheeler]

If you tell me how, perhaps I can give you a hand getting the circuit diagrams for the car. Can they be accessed with Lexia?

The older Lexia can access wiring diagrams however they are on a separate disc, when you go to select the diagram it will ask you to insert the disc number that the diagram is on.

[ozvtr]

I just didn't have access to the circuit at that moment in time.

I've assumed that the A/C is just the "manual" A/C. The only difference is the controller and resistor pack (labeled 8025 and 8026). The other type of controller would be the electronic versions, but the connections to the rest of the car would be the same. That is; 1 power line, 2 ground lines and 2 CAN lines.
The compressor is labelled 8020.
The evaporator sensor is labelled 8006.
The "high side" pressure sensor is labelled 8009.
The fresh/recycle air door actuator is 9070.
The BSM (labelled PSF1) electronically controls the compressor clutch. That is; there is no relay!
The engine ECU (1320) monitors the refrigerant high side pressure.
The BSI monitors the evaporator temp and requested temp then modulates the compressor clutch to attain a required average temp.
The A/C ECU (8025) derives a "temp" (not really) from the temp knob as requested by the user. This "temperature" is sent over a CAN BUS to the BSI. The BSI then compares the requested temp to the temperature at the evaporator. It the then sends a request over a CAN BUS to the BSM to increase or decrease the PWM of the compressor. If the high side pressure is too high or too low, the engine ECU sends a signal over a CAN BUS to stop the compressor from running.
The manual A/C doesn't actually set a temperature. It's really just warmer or cooler. The automatic A/C has a "sniffer" that senses the cabin temp and compensates to keep an actual cabin temperature.
The power for the compressor clutch comes out of pin 1 of the Yellow (JN) 5 pin connector on the BSM.
ALL the other signals are communicated over the CAN lines!!!
If the A/C is not working and you cant "talk" to the A/C ECU I would start looking at power and/or earths to the A/C ECU. A6, B2 and B4 of the A/C ECU connector.

By the way, if you have a manual slider to select fresh or recycled air on the "manual" A/C panel, there will be no actuator 8070.

[ozvtr]

Here is the climate control A/C circuit.
8045 and 8085 are all in the one unit, the cabin fan speed controller. They are not separate bits!
8050 is the cabin fan.
8030 is the "sniffer" that I mentioned.
8065 and 8071 are the temperature blend door actuator and the air outlet selector actuator.