BLUF (Bottom Line Up Front): 1988 ETM has an ERROR or omission in the A/C Compressor control wiring. The A/C control switch is fed by contacts in the air door sliders which de-energize the A/C when *BOTH* the footwell and dash vent air control sliders are all the way off. The position of the defrost vent slider is irrelevant.
Car: 11/1987 325iX (SN: 2550859)
Symptom: Air Conditioning compressor does not start. The A/C belt was off the compressor when I bought the car; I'm just now jumping into getting the A/C to work.
Troubleshooting log:
Checked high and low pressure cutoff switches (last circuit elements supplying power to the compressor) for voltage - No
Checked A/C control switch (on the center stack) for voltage at pin 4 (WT) - No
Checked fuse 20 for voltage - Yes
Checked C204 pin 7 (GR/BR) - Yes
Checked continuity from C204-7 female side to A/C Control Switch-4 - No
Swore
Tore apart center stack to find and access S230
Found S230 - No white wire
Swore more
Scratched head
The '88 E30 ETM shows that S230 receives current via a large GR/BR wire from C204-7, and has multiple GR/BR branches feeding various HVAC related loads, but also has a white branch feeding the A/C control switch.
Noticed that there was an undocumented branch of S230 sending a green/brown wire to an undocumented two pin connector that plugged into the air door slider assembly (where you slide the knobs to determine how much air comes out of the defrost, dash and footwell vents)
Noticed that the other pin of the undocumented two pin connector had a white wire.
Checked continuity from white wire in undocumented connector to A/C Control Switch pin 4 - Yes. This connector is not shown in the ETM diagrams.
Inspected the air door slider assembly...
There are contacts on both sides of a simple board between the dash and footwell vent sliders. Each slider has a wiper on it which bridges the contacts when it is moved to open the doors and opens the circuit when the doors are closed. The pins in the undocumented connector grip the board, touching both sides of the board, and thus both sets of contacts at once. That way advancing EITHER the dash vent slider OR the footwell vent slider completes the circuit and allows the A/C to operate.
I checked resistance across the dash vent slider contacts. Continuity was intermittent and resistance ranged from a couple of ohms up to 30-60 when there was continuity. Clearly age has dramatically reduced the reliability of this circuit element.
On further analysis of the circuit, it's apparent that the current that powers the A/C compressor clutch has to pass through these undocumented contacts... which is completely crazy. That current *SHOULD* be handled by a relay, while everything that currently handles that current remains a low current device and only acts to operate the relay.
I'm going to jumper the undocumented connector when I reassemble the center stack tomorrow morning. I will also take and post pics then. If I'm lucky my A/C will work. At some point in the future, I'll add a relay to power the compressor clutch and then I should/may be able to reconnect the undocumented connector... although I'll probably have to take the door slider assembly apart to polish the contacts to make them work again. I'm not very interested in doing that, however...
Pics:
The state of center stack tore-apartedness:
The undocumented connector and connection:
Dash vent door slider contacts:
Footwell vent door slider contacts:
The location of S230 in the harness -- the boxes are the recirculation door motor relays:
My jumper -- I had to use 12 ga wire, tin the ends and flatten them a bit with pliers, then reflow the solder to get them the right thickness to approximate the board and make strong consistent contact with the pins in the connector:
Car: 11/1987 325iX (SN: 2550859)
Symptom: Air Conditioning compressor does not start. The A/C belt was off the compressor when I bought the car; I'm just now jumping into getting the A/C to work.
Troubleshooting log:
Checked high and low pressure cutoff switches (last circuit elements supplying power to the compressor) for voltage - No
Checked A/C control switch (on the center stack) for voltage at pin 4 (WT) - No
Checked fuse 20 for voltage - Yes
Checked C204 pin 7 (GR/BR) - Yes
Checked continuity from C204-7 female side to A/C Control Switch-4 - No
Swore
Tore apart center stack to find and access S230
Found S230 - No white wire
Swore more
Scratched head
The '88 E30 ETM shows that S230 receives current via a large GR/BR wire from C204-7, and has multiple GR/BR branches feeding various HVAC related loads, but also has a white branch feeding the A/C control switch.
Noticed that there was an undocumented branch of S230 sending a green/brown wire to an undocumented two pin connector that plugged into the air door slider assembly (where you slide the knobs to determine how much air comes out of the defrost, dash and footwell vents)
Noticed that the other pin of the undocumented two pin connector had a white wire.
Checked continuity from white wire in undocumented connector to A/C Control Switch pin 4 - Yes. This connector is not shown in the ETM diagrams.
Inspected the air door slider assembly...
There are contacts on both sides of a simple board between the dash and footwell vent sliders. Each slider has a wiper on it which bridges the contacts when it is moved to open the doors and opens the circuit when the doors are closed. The pins in the undocumented connector grip the board, touching both sides of the board, and thus both sets of contacts at once. That way advancing EITHER the dash vent slider OR the footwell vent slider completes the circuit and allows the A/C to operate.
I checked resistance across the dash vent slider contacts. Continuity was intermittent and resistance ranged from a couple of ohms up to 30-60 when there was continuity. Clearly age has dramatically reduced the reliability of this circuit element.
On further analysis of the circuit, it's apparent that the current that powers the A/C compressor clutch has to pass through these undocumented contacts... which is completely crazy. That current *SHOULD* be handled by a relay, while everything that currently handles that current remains a low current device and only acts to operate the relay.
I'm going to jumper the undocumented connector when I reassemble the center stack tomorrow morning. I will also take and post pics then. If I'm lucky my A/C will work. At some point in the future, I'll add a relay to power the compressor clutch and then I should/may be able to reconnect the undocumented connector... although I'll probably have to take the door slider assembly apart to polish the contacts to make them work again. I'm not very interested in doing that, however...
Pics:
The state of center stack tore-apartedness:
The undocumented connector and connection:
Dash vent door slider contacts:
Footwell vent door slider contacts:
The location of S230 in the harness -- the boxes are the recirculation door motor relays:
My jumper -- I had to use 12 ga wire, tin the ends and flatten them a bit with pliers, then reflow the solder to get them the right thickness to approximate the board and make strong consistent contact with the pins in the connector:
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