P38A P38 Compressor wont start automatically

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P4wn33 said:
hehe I'm still allive and I will share the solution but I was not home last week and I didn't really have much time last week.. If the weather is okay, I will check all of that tomorrow :):) but first of all thanks to everyone to help me!
Click to expand...

Ok.. It's just raining right now.. I hope it will end in the near future
 
So.. I build a workaround and I think its perfect.. It has been working for 1000km and I think there no problem anymore...
My Solution: I buyed an second pressure switch.. the pressure switch is between the relai and ignition+, so I have automatically permanent 8 bar in the air tank..
But when I write this here, it occurs to me that I forgot the thermal switch.:confused::confused::confused:
 
Resurrecting this thread. Similar issue where compressor refuses to run on its own. Nanocom also refuses to run compressor. Can however run by removing relay and jumper to 2/5 ? Have swapped to new bosch relays (non orig yellow), one older yellow relay from another location hence know to 'work'. Have a fairly new (couple of years) fusebox. That said the relay seemed warmer than others. Checked fuses and also area with white plugs on LHS (passenger side) whre its in great condition (no rust or anything - just paint) etc. Any help troubleshooting is greatly appreciated.
 
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rrdude said:
Resurrecting this thread. Similar issue where compressor refuses to run on its own. Nanocom also refuses to run compressor. Can however run by removing relay and jumper to 2/5 ? Have swapped to new bosch relays (non orig yellow), one older yellow relay from another location hence know to 'work'. Have a fairly new (couple of years) fusebox. That said the relay seemed warmer than others. Checked fuses and also area with white plugs on LHS (passenger side) whre its in great condition (no rust or anything - just paint) etc. Any help troubleshooting is greatly appreciated.
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Thermal switch is fried. Check Technical Section for Wammers post where he details the part. Think I got mine from Farnell. If you're careful you can ease the board from the top of the compressor and then flatten what is left of the rivets back down to hold it on reassembly. Some people tap a couple of screws in.
 
If you have Nanocom, that will show the thermal switch state.

1695975677960.png
 
Thanks shows

Inlet valve:close
Thermal switch: Normal
Pressure Switch: OPEN
Lower Switch: open
Raise switch: open

From paulP38a, "for the compressor to operate automatically, the following conditions must be met:
  • Engine speed greater than 500rpm;
  • Pressure switch operational (open);
  • Thermal switch closed (grounded);
  • Exhaust valve solenoid closed;
  • Compressor Relay operational (closed) and MF2 not blown"
Have I missed something?

For what its worth, I also have removed 2 white connectors on passenger (LHS) even though connectivity was good and no corrosion or damage as I was in the area.
 
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Worn brushes in compressor ? Check the compressor actually gets 12V when the relay closes. Do this both with it connected and unplugged. Don't forget there's a splice in the feed from the relay, where it drives both the compressor and the diaphragm valve.
 
I can run the compressor with jumper at relay. NOT able to run with nanocom too btw. When run via relay it gets the car off bumpstop in about 4/5 min from empty so internals of the compressor appear good. Mystified why it wont run on its own as conditions for it to run in #67 above appear to be met.
 
pwood999 said:
Worn brushes in compressor ? Check the compressor actually gets 12V when the relay closes. Do this both with it connected and unplugged. Don't forget there's a splice in the feed from the relay, where it drives both the compressor and the diaphragm valve.
Click to expand...
Whats best way to check this?
 
rrdude said:
Whats best way to check this?
Click to expand...
If the compressor runs from a relay jump, the brushes are OK. Does the relay operate from the EAS ECU? If not, either there is a bad connection from the EAS ECU to the relay, a bad connection from the thermal switch, or a fault present in the ECU, the compressor will not run with fault present. I's likely to be a wiring or connector fault IMO. The connectors in the EAS box are well known for failing to make good contact, the contacts become slack with age.
 
Datatek said:
If the compressor runs from a relay jump, the brushes are OK. Does the relay operate from the EAS ECU? If not, either there is a bad connection from the EAS ECU to the relay, a bad connection from the thermal switch, or a fault present in the ECU, the compressor will not run with fault present. I's likely to be a wiring or connector fault IMO. The connectors in the EAS box are well known for failing to make good contact, the contacts become slack with age.
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Unsure how to test if EAS ECU runs relay. Guess nanocom could be used to listen to relay?
Won't run with orange wire grounded.

@Datatek When you mean eas box, do you mean the connecters under the valve block? In engine bay rather than the ECU under passenger (LHS) seat?
The drivers side (RHD) white connectors have not been removed as no apparent corrosion/damage visible therefore just cleaned them with contact cleaner for now (wonder if there is any wiring for this going through those connectors)

Thanks again
 
rrdude said:
Unsure how to test if EAS ECU runs relay. Guess nanocom could be used to listen to relay?
Won't run with orange wire grounded.

@Datatek When you mean eas box, do you mean the connecters under the valve block? In engine bay rather than the ECU under passenger (LHS) seat?
The drivers side (RHD) white connectors have not been removed as no apparent corrosion/damage visible therefore just cleaned them with contact cleaner for now (wonder if there is any wiring for this going through those connectors)

Thanks again
Click to expand...
Yes, I mean the connectors in the box under the bonnet.
The white connectors are a well known source of problems, the only certain long term fix is to cut them out and solder the wires.
Nanocom should let you turn on the compressor so you can then check if the relay operates either visually with the cover off, or with a DVM across the coil contacts.
 
Nanocom should run the compressor manually even if the thermal switch is bad (which you have shown above is ok). +1 on ECU will not run it if there are faults present, so check & clear first.

ECU to Relay wire is direct, so cannot be the footwell connections. Needs a voltmeter to check if the 12V & Ground are getting to the relay.
1696069659775.png
 
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