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Wiring/ECU gurus, some assistance please


89Mirageman
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Galant VR-4 org Post #: 1211458 posted 07/04/15 06:39 PM     Remind Me!  Send Private Message   Edit Post      
This is actually for my 92 Colt but I'm sure you guys can still help. I recently installed AC and wired it all up but have a problem with it working intermittently. I have checked and double checked my wiring and it seems to be correct. I am using a 92 2.0 DOHC DSM engine harness and ECU. I have the AC wiring schematics from my colt FSM below. The wire in question is circled in red. It seems this wire is supposed to be grounded by the ECU on pin 65. In my DSM FSM it's also pin 65 but the wire is red with a black stripe. If I ground this wire to the chassis manually the compressor's clutch kicks on and cold air starts coming out of the vents. My question is, what actually tells the ECU to ground this wire?

If I were to run a separate wire from pin 65 and just ground it would this fix my problem? Is that safe to do? Any help is greatly appreciated and I have both manuals if you guys need to see anything else.






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Edited by 89Mirageman (07/05/15 12:09 PM)

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Galant VR-4 org Post #: 1211466 posted 07/04/15 10:16 PM     Remind Me!  Send Private Message   Edit Post      
"My question is, what actually tells the ECU to ground this wire?"

That is the big question. I would check the other diagram pages for any wiring from the compressor control unit shown on the given page, that is connected to the ECU through that same connector, c23. You could ground that wire like you have tested, but then do you have control of the on/off function with the a/c switch?



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tektic
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Galant VR-4 org Post #: 1211471 posted 07/05/15 06:13 AM     Remind Me!  Send Private Message   Edit Post      
I had a similar issue with my a/c all of a sudden not working. I asked my uncle who is a retired refrigerator repair man. He said the only things there would be a switch, a temp sensor, or a low pressure sensor. off hand I couldn't tell you. but if the switch works independently of this pin than check your sensors.

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89Mirageman
It's no Mirage, man


Galant VR-4 org Post #: 1211474 posted 07/05/15 08:52 AM     Remind Me!  Send Private Message   Edit Post      
I went back out yesterday afternoon and grounded that wire and just let the car run for a while with the AC on. After a few minutes the clutch kicked off and started cycling normally. Needless to say I was stoked. I ended up just letting it run for another 10-15 minutes with zero issues, blowing ice cold the entire time and the clutch was acting normal.

I was also wondering what made the ecu ground that pin but I guess it doesn't matter now. Also to answer your question the AC only works when I cut it on. Grounding that pin didn't bypass the switch on the HVAC panel or anything.

On the colt the low/high pressure switch is built into one. I tested it with some instructions that I found online. Also the green wire going to it had juice when the AC switch was cut on so all that checked out ok as well. It was just this one ground causing me issues the entire time.



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tektic
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Galant VR-4 org Post #: 1211480 posted 07/05/15 09:18 AM     Remind Me!  Send Private Message   Edit Post      
Do you have the coolant switch in the thermostat housing wired up? I'm pretty surea broken wire there is keeping my compressor from comming on.

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GSTwithPSI
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Galant VR-4 org Post #: 1211484 posted 07/05/15 11:10 AM     Remind Me!  Send Private Message   Edit Post      
Chris,

The wire going to pin 65 is grounded by the ECU through IC109. IC109 is activated with the key in the ON position and the engine running/cranking. This driver also controls the fuel pump via the MFI relay (pin 56), so chances are, if you're fuel pump is working as it should be the driver is functioning properly. You could pull the ECU and do a visual inspection to verify. You can use this thread to assist you: click . It will be the driver closest to the edge of the circuit board. Check it for any sign of damage.

If you run a wire from pin 65 to ground, you'll basically be activating the compressor relay at all times so long as the dual pressure switch is in its operational window and it's receiving power (need to see the other side of the diagram to determine when it's receiving power). The wire going to pin 65 basically gives the ECU the ability to control the A/C under certain conditions. I'm not clear on the exact logic, but I believe the ECU will shut off the A/C under WOT conditions, and also if it sees the car overheat (unsure of exact temperature). If you ground the wire going to pin 65, you remove the ECU's ability to control the A/C. Just FYI, pin 7 (A/C coolant temp switch input) tells the ECU to bump the idle when the A/C is on, so you can verify this is working just by observing how the car behaves with the compressor on.

I'd need to see the other side of the diagram to tell how grounding pin 65 would affect the system overall (where wires 1, 2 and 3 go pictured upper top left hand corner). As long as the dual pressure switch only sees power with the compressor control unit activated, I'd think you would be fine grounding pin 65. For the most part, the wire going to pin 65 should go to ground the majority of the time with the vehicle on and running anyways.



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Edited by GSTwithPSI (07/05/15 11:17 AM)

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89Mirageman
It's no Mirage, man


Galant VR-4 org Post #: 1211488 posted 07/05/15 11:44 AM     Remind Me!  Send Private Message   Edit Post      
Quoting tektic:

Do you have the coolant switch in the thermostat housing wired up? I'm pretty surea broken wire there is keeping my compressor from comming on.




Yes, it's wired up just as it should be in the dsm it came from. I didn't really modify the engine harness much other than removing some wires for the cruise control since I knew I wasn't going to be using that. I just used the wires that would normally connect the engine harness to the dash harness and soldered up an adapter to plug in between the dsm engine harness and my colt's dash harness. I even put in a brand new temp sensor when the engine was rebuilt.



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95 Eagle Summit DL coupe
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89Mirageman
It's no Mirage, man


Galant VR-4 org Post #: 1211489 posted 07/05/15 11:57 AM     Remind Me!  Send Private Message   Edit Post      
Quoting GSTwithPSI:

Chris,

The wire going to pin 65 is grounded by the ECU through IC109. IC109 is activated with the key in the ON position and the engine running/cranking. This driver also controls the fuel pump via the MFI relay (pin 56), so chances are, if you're fuel pump is working as it should be the driver is functioning properly. You could pull the ECU and do a visual inspection to verify. You can use this thread to assist you: click . It will be the driver closest to the edge of the circuit board. Check it for any sign of damage.

If you run a wire from pin 65 to ground, you'll basically be activating the compressor relay at all times so long as the dual pressure switch is in its operational window and it's receiving power (need to see the other side of the diagram to determine when it's receiving power). The wire going to pin 65 basically gives the ECU the ability to control the A/C under certain conditions. I'm not clear on the exact logic, but I believe the ECU will shut off the A/C under WOT conditions, and also if it sees the car overheat (unsure of exact temperature). If you ground the wire going to pin 65, you remove the ECU's ability to control the A/C. Just FYI, pin 7 (A/C coolant temp switch input) tells the ECU to bump the idle when the A/C is on, so you can verify this is working just by observing how the car behaves with the compressor on.

I'd need to see the other side of the diagram to tell how grounding pin 65 would affect the system overall (where wires 1, 2 and 3 go pictured upper top left hand corner). As long as the dual pressure switch only sees power with the compressor control unit activated, I'd think you would be fine grounding pin 65. For the most part, the wire going to pin 65 should go to ground the majority of the time with the vehicle on and running anyways.




GST, thanks so much for this info. At first I was afraid that if I simply grounded that one wire that my compressor's clutch would constantly be on and the ac would never cycle as it should. Like I said, I ran a simple test yesterday and let the car run for 10-15 min and it cycled off and on normally. Also for some reason the schematics show that once power comes in from the LR (light blue/red) wire, pin #3 on connector A-24 that it should send power to pin 1, the yellow wire. In my case this was not happening and that yellow wire never saw power. Once I grounded that black/white wire (pin #4) it worked as it should and the yellow wire saw power once the ac was switched on.

I see what you're saying about the AC shutting down if the car overheats or under WOT. This is my DD and it never sees WOT and I always keep an eye on my gauges so I think I'll be good there. Honestly, its hot and humid as hell here every day in the summer here in NC so I just want the AC blowing cold at this time. I plan to re-visit it this fall when I can comfortably work on it and maybe see what I have wrong. For now if grounding that wire will safely make my AC work, that's what I'm going to do. I will still scan the other pages of the wiring schematics for you guys to take a look at. Maybe fresh eyes will see something I don't. I don't know about you guys but I can only concentrate on wiring for an hour or so at a time and it all starts to look the same after that and I get frustrated.



93 Mitsubishi Expo LRV
95 Eagle Summit DL coupe
98 Mitsubishi Mirage DE coupe

Posts: 2502 | From: Stantonsburg, NC | Member Since: 07/05/06 | IP: (71.52.129.43) | Report this post to a Moderator

89Mirageman
It's no Mirage, man


Galant VR-4 org Post #: 1211490 posted 07/05/15 12:10 PM     Remind Me!  Send Private Message   Edit Post      
I just added the other two pages of AC wiring to the original post at the top.



93 Mitsubishi Expo LRV
95 Eagle Summit DL coupe
98 Mitsubishi Mirage DE coupe

Posts: 2502 | From: Stantonsburg, NC | Member Since: 07/05/06 | IP: (71.52.129.43) | Report this post to a Moderator

GSTwithPSI
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Galant VR-4 org Post #: 1211503 posted 07/05/15 03:21 PM     Remind Me!  Send Private Message   Edit Post      
Yeah, looking at the other page, it looks like you'll be just fine bypassing the ECU. Pin 6 (green wire) coming from the compressor control unit looks like it pretty much powers the entire circuit, starting with the dual pressure switch. Page 8-84 are just the fan circuits, which are also powered indirectly by the compressor control unit.

The way you have it wired now definitely won't hurt anything. I'd leave it be if the A/C is working well.

If you do eventually want to troubleshoot it, I'd start by finding connector A-19. From that connector, I'd test for continuity from pin 2 on A-19 to pin 4 on connector A-24X (at the compressor relay coil). Then, I'd test for continuity from pin 2 on A-19 to ECU pin 65. Basically, you'll want to verify you have a solid connection from the compressor relay coil to the ECU. Like I said, if your fuel pump is working, I doubt the ECU driver is to blame, which tells me you probably have a wiring issue somewhere between the compressor relay coil and ECU.



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89Mirageman
It's no Mirage, man


Galant VR-4 org Post #: 1211513 posted 07/05/15 05:36 PM     Remind Me!  Send Private Message   Edit Post   
Thanks again. Found something interesting as well. On the colt the AC wiring doesn't have anything to do with the engine's temp sensor. At least not from what I can tell. On the dsm, it does just like tektic mentioned earlier. Maybe that's my issue and why I had to ground that wire. Who knows? All I know is the AC blows ice cold and I'm happy .



93 Mitsubishi Expo LRV
95 Eagle Summit DL coupe
98 Mitsubishi Mirage DE coupe

Posts: 2502 | From: Stantonsburg, NC | Member Since: 07/05/06 | IP: (71.52.129.43) | Report this post to a Moderator


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