VW A/C Compressor

Forum on Volkswagen related hardware, so VW, Audi, Seat, Skoda etc.
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Re: VW A/C Compressor

Post by muehlpower »

according to my program it should be like this:


back message:
ID 33 (0x61)
length 8 Byte / ENHANCED Checksum
Byte 0 =1 at HV voltage under 200V, =0 above 200V (below 200V it want work, so its a kinde of HV OK)
Byte 1 =112, always, i dont know why
Byte 2 =RPM as set via PID=32 in Byte 0
(Byte 3 =110 below 200V, =14 above 200V, =46 when er running)
Byte 3 bit 6= HV not OK
Byte 3 bit 5= running
Byte 5 =temperature 160 at 24°C, i don't know the scaling and what themperature that is til now
Byte 6 =54 at 109V, =28 at 56V =83 at166V scaling: Voltage/2
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Re: VW A/C Compressor

Post by crasbe »

muehlpower wrote: Sun Feb 06, 2022 9:56 am according to my program it should be like this:


back message:
ID 33 (0x61)
length 8 Byte / ENHANCED Checksum
Byte 0 =1 at HV voltage under 200V, =0 above 200V (below 200V it want work, so its a kinde of HV OK)
Byte 1 =112, always, i dont know why
Byte 2 =RPM as set via PID=32 in Byte 0
(Byte 3 =110 below 200V, =14 above 200V, =46 when er running)
Byte 3 bit 6= HV not OK
Byte 3 bit 5= running
Byte 5 =temperature 160 at 24°C, i don't know the scaling and what themperature that is til now
Byte 6 =54 at 109V, =28 at 56V =83 at166V scaling: Voltage/2
Now you have Byte 3 defined twice 🤔
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Re: VW A/C Compressor

Post by muehlpower »

Yes, but different Bits of Byte 3!
If HV is not OK Bit6 and Bit5 are high. (Byte3 = 110)
If HV is OK but A/C is not running Bit5 and Bit6 are low. (Byte3 = 14)
If HV is OK and A/C is Running Bit5 is high, Bit6 is low. (Byte3 = 46)
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Re: VW A/C Compressor

Post by EV_Builder »

How do you control / manage pump speed/power/flow?
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Re: VW A/C Compressor

Post by muehlpower »

EV_Builder wrote: Fri Apr 22, 2022 9:57 pm How do you control / manage pump speed/power/flow?
to control the A/C
ID 32 (0x20)
length 6 Byte / ENHANCED Checksum
Byte 0 =RPM (dec 20-250)
Byte 1 bit 2 = aktivate
Byte 1 bit 0 = start
Byte 2-5 = 0

There is also a high pressure side sensor reporting on the LIN bus.
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Re: VW A/C Compressor

Post by EV_Builder »

Do you manage the pressure and temperatures yourself?
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Re: VW A/C Compressor

Post by muehlpower »

EV_Builder wrote: Sun Apr 24, 2022 4:36 pm Do you manage the pressure and temperatures yourself?
A DUE is planned and installed, but I haven't put it into operation yet.
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Re: VW A/C Compressor

Post by EV_Builder »

muehlpower wrote: Tue Apr 26, 2022 9:17 am A DUE is planned and installed, but I haven't put it into operation yet.
Let me know how that goes because i still ow you a nice RIO device 8-) :)
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Re: VW A/C Compressor

Post by Pete9008 »

Hi, What baud rate does the VW LIN bus run at? (I have had a look through the forum posts and the wiki but can't seem to find this).

I've got some I-Pace air con valves that run LIN at 9600, the VW compressor and the VW heater and I'm wondering whether they could all coexist on the same bus.
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Re: VW A/C Compressor

Post by muehlpower »

Pete9008 wrote: Tue Jul 05, 2022 9:34 am Hi, What baud rate does the VW LIN bus run at? (I have had a look through the forum posts and the wiki but can't seem to find this).

I've got some I-Pace air con valves that run LIN at 9600, the VW compressor and the VW heater and I'm wondering whether they could all coexist on the same bus.
VW uses 19200 baud. I run heater, compressor and the VW A/C pressure sensor on the same LIN bus.
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Re: VW A/C Compressor

Post by Pete9008 »

muehlpower wrote: Tue Jul 05, 2022 1:09 pm
Pete9008 wrote: Tue Jul 05, 2022 9:34 am Hi, What baud rate does the VW LIN bus run at? (I have had a look through the forum posts and the wiki but can't seem to find this).

I've got some I-Pace air con valves that run LIN at 9600, the VW compressor and the VW heater and I'm wondering whether they could all coexist on the same bus.
VW uses 19200 baud. I run heater, compressor and the VW A/C pressure sensor on the same LIN bus.
Thanks, thought I'd seen a reference to 19200 somewhere (although I couldn't find it when I went looking).

Looks like it will best to plan for two separate buses, one for VW and one for the Jaguar bits :(

I plan to use the VW pressure sensor too - Thanks for sharing all the information on how to talk with the VW parts!
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Re: VW A/C Compressor

Post by muehlpower »

Pete9008 wrote: Tue Jul 05, 2022 2:05 pm
muehlpower wrote: Tue Jul 05, 2022 1:09 pm
Pete9008 wrote: Tue Jul 05, 2022 9:34 am Hi, What baud rate does the VW LIN bus run at? (I have had a look through the forum posts and the wiki but can't seem to find this).

I've got some I-Pace air con valves that run LIN at 9600, the VW compressor and the VW heater and I'm wondering whether they could all coexist on the same bus.
VW uses 19200 baud. I run heater, compressor and the VW A/C pressure sensor on the same LIN bus.
Thanks, thought I'd seen a reference to 19200 somewhere (although I couldn't find it when I went looking).

Looks like it will best to plan for two separate buses, one for VW and one for the Jaguar bits :(

I plan to use the VW pressure sensor too - Thanks for sharing all the information on how to talk with the VW parts!
The LIN master causes devices to synchronize, for which the sync bits are sent by the master. It can easily be that the Jaguar parts also run with 19200.
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Re: VW A/C Compressor

Post by Pete9008 »

muehlpower wrote: Tue Jul 05, 2022 4:41 pm The LIN master causes devices to synchronize, for which the sync bits are sent by the master. It can easily be that the Jaguar parts also run with 19200.
I've already tried the Jaguar valves at all the standard baud rates and 9600 was the only one that they would respond to.

It's a good idea though, what I should to do is try the VW parts at 9600baud to see if they will respond to that. Do you know whether they need HV connected to respond to LIN status requests or is the 12V enough by itself?
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Re: VW A/C Compressor

Post by muehlpower »

Pete9008 wrote: Tue Jul 05, 2022 5:26 pm
muehlpower wrote: Tue Jul 05, 2022 4:41 pm The LIN master causes devices to synchronize, for which the sync bits are sent by the master. It can easily be that the Jaguar parts also run with 19200.
I've already tried the Jaguar valves at all the standard baud rates and 9600 was the only one that they would respond to.

It's a good idea though, what I should to do is try the VW parts at 9600baud to see if they will respond to that. Do you know whether they need HV connected to respond to LIN status requests or is the 12V enough by itself?
you get an answer from the compressor on PID[33] = 0x61 and one from the heater on PID[48] = 0xF0, even without HV
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Re: VW A/C Compressor

Post by EV_Builder »

muehlpower wrote: Tue Jul 05, 2022 4:41 pm The LIN master causes devices to synchronize, for which the sync bits are sent by the master. It can easily be that the Jaguar parts also run with 19200.
No LIN expert here, but I think that those sync bits are to fine tune the baudrate for cable impedance etc. don't think that more then a double speed would be considered a valid bus timeing. Imagine a bad LIN wire and slave devices adjusting the bus speed. That said maybe slaves do support auto baud on boot and later use the sync to lock the timeing. Easy to test anyway.
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Re: VW A/C Compressor

Post by muehlpower »

EV_Builder wrote: Tue Jul 05, 2022 6:50 pm
muehlpower wrote: Tue Jul 05, 2022 4:41 pm The LIN master causes devices to synchronize, for which the sync bits are sent by the master. It can easily be that the Jaguar parts also run with 19200.
No LIN expert here, but I think that those sync bits are to fine tune the baudrate for cable impedance etc. don't think that more then a double speed would be considered a valid bus timeing. Imagine a bad LIN wire and slave devices adjusting the bus speed. That said maybe slaves do support auto baud on boot and later use the sync to lock the timeing. Easy to test anyway.
on https://www.ni.com/de-de/innovations/wh ... --bus.html you can read

"
2.Sync
The synchronization field is the second one transmitted by the master task in the header. Sync is defined as the x55 hexadecimal character. The sync field allows slave devices that perform automatic baud rate detection to measure the period of the baud rate and synchronize their internal baud rate to the bus.
"
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Re: VW A/C Compressor

Post by EV_Builder »

Ok you might be right.

In order tobe right myself the "feature" definition of 'automatic baud rate detection' should mean x % over a given baud rate. Not like total buspeed variations.

If you are right then i still find it odd that a automotive bus would be setup 'plug and play' style since there priority is reliability and not compatibility... Let's see if we find a multispeed automotive part :) since implementation can differ from specification.
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Re: VW A/C Compressor

Post by muehlpower »

I agree that most OEM devices don't have this feature, but it's worth a try.
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Re: VW A/C Compressor

Post by Pete9008 »

muehlpower wrote: Thu Jul 07, 2022 7:29 am I agree that most OEM devices don't have this feature, but it's worth a try.
Agree completely, which is why I've just tested them!

Unfortunately they only respond to 19200 baud but it was definitely worth a try.

What's more interesting is that the IDs and message contents don't all match with your results. I'm guessing that the comms may vary from model to model or generation to generation. I've only looked at the status message as I have no HV supply connected.

Compressor - part No 12E-820-803-E
Sends status on ID 0x21, extended checksum, 19200baud, message contents - 00:f0:e8:ff:ff:ff:ff:ff

Heater - part No 3Q0-963-231-E
Sends status on ID 0x30, extended checksum, 19200baud, message contents - 00:fc:c0:80:7e:48:46:46

I think the compressor ID may match yours (I think you have included the address parity bits?) The data seems different (unless this is because I don't have HV on it?). The heater matches yours.

I'll do a bit more investigation once I have a HV supply available.

Regarding the autobaud it is definitely in the spec but doubt it gets implemented that often. It's a feature that would be of minimal benefit to automotive manufacturers although it may be more common among generic sensor suppliers (to avoid multiple software versions). It's probably is used as standard by low cost sensors (ones without a crystal or resonator that instead use low accuracy RC or on chip oscillators) to tune their baud rates to accurately match the bus.
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Re: VW A/C Compressor

Post by muehlpower »

Pete9008 wrote: Thu Jul 07, 2022 8:52 am
muehlpower wrote: Thu Jul 07, 2022 7:29 am I agree that most OEM devices don't have this feature, but it's worth a try.
Agree completely, which is why I've just tested them!

Unfortunately they only respond to 19200 baud but it was definitely worth a try.

What's more interesting is that the IDs and message contents don't all match with your results. I'm guessing that the comms may vary from model to model or generation to generation. I've only looked at the status message as I have no HV supply connected.

Compressor - part No 12E-820-803-E
Sends status on ID 0x21, extended checksum, 19200baud, message contents - 00:f0:e8:ff:ff:ff:ff:ff

Heater - part No 3Q0-963-231-E
Sends status on ID 0x30, extended checksum, 19200baud, message contents - 00:fc:c0:80:7e:48:46:46

I think the compressor ID may match yours (I think you have included the address parity bits?) The data seems different (unless this is because I don't have HV on it?). The heater matches yours.

I'll do a bit more investigation once I have a HV supply available.

Regarding the autobaud it is definitely in the spec but doubt it gets implemented that often. It's a feature that would be of minimal benefit to automotive manufacturers although it may be more common among generic sensor suppliers (to avoid multiple software versions). It's probably is used as standard by low cost sensors (ones without a crystal or resonator that instead use low accuracy RC or on chip oscillators) to tune their baud rates to accurately match the bus.
in my post the PID[30] and PID[48] are decimal, in hex it would be 0x21 and 0x30
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Re: VW A/C Compressor

Post by Pete9008 »

muehlpower wrote: Thu Jul 07, 2022 10:43 am in my post the PID[30] and PID[48] are decimal, in hex it would be 0x21 and 0x30
OK, thanks, had been looking at your first post which gives all compressor message data and gives ID 31 (0x61) for the return address and had missed your later post.

Regarding the heater, your earlier post suggests that the power is controllable :
The feedback comes on ID48. Byte 0 is power. 13 for 770W, 26 for 1540W. ID28 is sent for control. Byte 0 is power, last bit of byte 1 starts and stops
Am I understanding this correctly? The reason I ask is that the data sheet linked in the 3rd post on this thread just gives two power levels, 5kW and 7kW (although it's not a very detailed data sheet)

If the power is adjustable then I can rig up a low current power supply to test it. Do you know what the minimum setting is, could it be run briefly at minimum power without coolant?

If it is fixed at 5kW or 7kW then I'll need to wait till I can connect it to batteries and it has coolant in it.
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Re: VW A/C Compressor

Post by muehlpower »

PID-tabelle.png
This is the complete table of all LIN addresses. According to this table "Id-dec" I send the commands for A/C at 32 and for heater at 28 and get feedback from A/C at 33 and from the heater at 48. 31 in my first post is wrong, I will correct.
The heating performance can be specified by byte 0 at Id28 and observed at Id48 byte 0
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Re: VW A/C Compressor

Post by EV_Builder »

Just to add / clarify for the purist, no offence, the difference between ID and PID are the two parity bits. Both of them make one byte. So there are only 6bits for an ID. That's why we have 63 Addresses maximum.
IMHO we should talk ID not PID.
PID is implementation level.
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Re: VW A/C Compressor

Post by golfdubcrazy »

hi its been a while. i had some free time today and was working decoding the pressure reading from the factory sensor. i connected upto the heater control on my work bench and send the can wakeup signal and connected VCDS to read the ac pressure sensor values. i then emulator the lin bus signals to see the VCDS sensor reading.
the pressure sensor partnumber is 5Q0 959 126A


40 F8 2F 22 1bar 0100 0000 1111 1000

01 01 01 01 4bar 0000 0001 0000 0001
05 01 01 01 4.2bar 0000 0101 0000 0001
20 01 01 01 4.6bar 0010 0000 0000 0001

30 01 01 01 4.8 bar 0011 0000 0000 0001

40 01 01 01 5.0bar

aa 01 01 01 6.8bar

bb 01 01 01 7.0bar

cc 01 01 01 7.4 bar

dd 01 01 01 7.6 bar

ee 01 01 01 7.8 bar

ff 01 01 01 8.2bar 1111 1111 0000 0001


ff 02 01 01 12.2 bar 1111 1111 0000 0010

ff 03 01 01 16.4bar 1111 1111 0000 0011

ff 04 01 01 20.4 bar 1111 1111 0000 0100

ff 05 01 01 24.6 1111 1111 0000 0101

ff 06 01 01 28.8 1111 1111 0000 0110

cc 07 01 01 32.0 1111 1111 0000 0111

dd 07 01 01 32.4

ee 07 01 01 32.6



cc 10 01 01 3.2 1100 1100 0001 0000



3e 01 01 01 5 bar 0011 1110 0000 0001

01 02 01 01 8.2 bar 0000 0001 0000 0010

3e 02 01 01 9.2 bar

3e 03 03 02 13.2 bar

it looks like the pressure data is the first two bytes and is a 12bit value hope this helps bits 0-8 = 0-4bar bits 9-12 = pressure + 4bar
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Re: VW A/C Compressor

Post by Pete9008 »

Thank you :D

I bought one of those sensors a while ago and that has been on my to do list ever since!

Edit - Curious what it looked like so plotted it:
5Q0959126A.png
Pretty good, you must have taken a bit of care taking those measurements!

Pressure is on the y and message value on the x so that the regression equation is more useful.

Pressure(Bar) = 0.088645 * (Byte0 + (256 * Byte1))

Note - there is something odd going on at pressures below 4bar - the output starts going up again. Wondering whether bytes 2 and 3 need to be used in this region too?

Edit2 - BTW if you are looking for one of these sensors on ebay it's worth searching for VW AC pipes rather than the part number. There are a number of pipes for sale, complete with the sensor, mounting boss/valve and often wiring pigtails for less than the second hand sensor alone (a bit of care is required to make sure it's off a car that had the pressure sensor rather than the pressure switch though). I got mine for around £10 this way.
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