Resolved 2G A/C system not working

cswindel · Aug 4, 2026

Alright electrical nerds I need to be graced with you assistance as I am no good with electrical.

Current situation:
- A/C is not blowing cold air although the system has been charged recently without the system actually pulling in r-134 because well it dont work haha
- I dont have any prior knowledge of whether it worked or not before or after my teardown of the car
- As a side note I am running OHM harnesses throughout the engine bay and interior and running ECMLink v3

Current untested areas and possible theories:
- A/C compressor is dead and I have not ran 12v power to it such that I can test if the clutch engages or not
- Seeing if there is a setting in ECMLink that I am missing since the a/c and rad fan both kick on when signal for rad fan to kick on gets pushed out
- Thermo sensor is poop but havent checked and the wiring diagrams confuse me on where it is physically located behind the glove box and there arent really any pictures when i look.
- ACCU is poop but havent checked and not sure which wires in the connector to check but havent dug into that area yet because its a pain to reach

Steps I have taken thus far:
- Checked continuity from ECU pin 22 to A/C compressor relay in fuse box (Good continuity)
- With key in ON position and engine not running, I have voltage going to the a/c fan (connector A-39), Dual pressure switch (A-47), and the A/C compressor (A-95)
- With the engine running I checked for voltage at the same connectors and nothing concerning
- With the engine running and a/c switch active I checked voltage again and still nothing concerning. A/C compressor ground showed grounding too.
- With the engine running, I jumped/bypassed the dual pressure switch and no result came about from that
- As mentioned prior, I noticed that the a/c fan and rad fan kicked on at the same time when the signal for the rad fan got passed through the circuit (I dont know if this is normal or not but hey 2 fans is better than 1).

Just wanting to see what your inputs are with this matter before I start going down unnecessary rabbit holes without much guidance (because I will get lost, sad, and confused and it might all occur simultaneously). I believe I have covered the majority of what I have done and assessed to get this thread rolling at least

Vladimir · Aug 12, 2026

And just one more thing. Verify that you've done all the continuity test correctly. My brother was next to me and he asked what I'm typing and trying to explain. His first question was " are you sure he knows what you even mean, when you talk to him?". I a lot of time forget that the most simple tasks to an everyday tech can be difficult or hard to understand to people that don't wrench for a living. I'll add a video

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Well partially, yes. Do you have your old harness to see if there was pin 42 to begin with, because according to everyone 2g pinout diagram I found pin 42 must go to pressure switch. All the diagrams also show there is a pin from ECU going directly to press switch. They might have the pin numbers wrong, but the routing itself should be correct. I have a 1st gen, I can't verify on mine unfortunately

cswindel · Aug 12, 2026

Yeah so what i did was i put my multimeter in the continuity setting and stuck one probe in one pin of the dual pressure switch. Then I went inside the car and began using the other probe to contact each pin of both black box connectors. Then I took the probe in the dual pressure switch, put it in the other pin and probed the connectors for the black box again. All the connectors for both components were disconnected so I did a front probe rather than a back probe of the connectors.

I back probed pin 45 of the ECU, then took the other probe to the disconnected pressure switch connector and probed both pins of that connector

Vladimir said:
Well partially, yes. Do you have your old harness to see if there was pin 42 to begin with, because according to everyone 2g pinout diagram I found pin 42 must go to pressure switch. All the diagrams also show there is a pin from ECU going directly to press switch. They might have the pin numbers wrong, but the routing itself should be correct. I have a 1st gen, I can't verify on mine unfortunately

No unfortunately not. Even if I did have it that harness was a hacked nightmare honestly. Poor thing didnt deserve it

Vladimir · Aug 12, 2026

When you are in continuity setting and touch both leads together, do you get a beep?

cswindel · Aug 12, 2026

Yeah i do

Vladimir · Aug 12, 2026

Ok. I believe that you did everything correctly and that means that the last post that I've sent with the underlined diagram is correct, everything else that's happening makes sense, why no condenser Fan, and no power at the pressure switch without you jumping the clutch/relay etc... there is plenty more we can trace like power coming out of the A/c switch and wiring from ECU and black box etc... but I would try to see if OHM got a schematic.

I would honestly just try calling or emailing them, asking why pin 42 is missing and doesn't go to press switch. And ask them if they made changes on how the a/c system gets engaged etc .. maybe they'll answer if not we can continue.... I don't mind, on my free time.

cswindel · Aug 12, 2026

Vladimir said:
Ok. I believe that you did everything correctly and that means that the last post that I've sent with the underlined diagram is correct, everything else that's happening makes sense, why no condenser Fan, and no power at the pressure switch without you jumping the clutch/relay etc... there is plenty more we can trace like power coming out of the A/c switch and wiring from ECU and black box etc... but I would try to see if OHM got a schematic.

I would honestly just try calling or emailing them, asking why pin 42 is missing and doesn't go to press switch. And ask them if they made changes on how the a/c system gets engaged etc .. maybe they'll answer if not we can continue.... I don't mind, on my free time.

I appreciate this more than you know

Vladimir · Aug 13, 2026

Great news, there is actually 2 different diagram styles for 2g dsm. I found one that matches exactly. And that pinouts are all matching. This is actually the one we need. There is no pin 42 that is in the pinout diagram for the ecu. It still doesn't explain why you have no continuity going to from the black box going to g/o wire to dual press switch, but we can tackle it a bit different now. Maybe something went wrong with the way you tested the pins or there is just an open on one side. I'll have time later today. We can start with simple things without taking things apart and go deeper.

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Vladimir · Aug 13, 2026

Ok we are gonna concentrate on the black box , since we confirmed OHM racing did include 2 pinned wires for pin 45 and pin 22 goes to ground side relay control. This shows confirms that they actually include A/c wiring ( or at least partially).

All of your wiring on the black box should be untouched by OHM racing and all the wire should match the colors and pins. You are gonna be using a multimeter and a 12v test light from here.

Make sure your cars ignition is ON or the (car might have to even run) but try only ignition on first. Make sure you set your blower to LO, you set your temp to LO, your A/C switch is pressed ON and the light for the a/c goes on.

Go to the black box and test this points With multimeter and test light to ensure there is enough current present. Start by checking LB wire at pin 2 it should have solid 12v. Next check that pin3 Black wire has a good ground. If they both have power and ground go to PIN 1, G-O wire use your test light and a multimeter, it should be solid 12v there IF there is no power coming out of G-O we would have to test the FIN thermo sensor , but for now just test those 3 points and skip the thermo.

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Remember, you are my eyes and hands, I don't have a 2g to confirm how everything is wired, I'm only going based on your words and diagrams, so if you see anything weird or something that doesn't make sense LMK. Also add pictures of connectors etc......

cswindel · Aug 13, 2026

Yeah man i can do that. Is it okay if I dont have a 12v test light at the moment? I can order one but can I accomplish most of this with multimeter only?

Vladimir · Aug 13, 2026

You can do it without but if you have a regular bulb with a socket like h11 or something, you can always make that your test light. Just put pins on the 2 wires to probe things. Load testing is always better , because sometimes you can have corrosion inside a connector or a partially broken wire, it will show good voltage and continuity but would not be able to take a load.

cswindel · Aug 13, 2026

Oh sweet I can do that! I got some extra lying around. I've still got a few hours at work but I'll get back to you once I have some results

cswindel · Aug 16, 2026

Is the connector supposed to be B-49? If so, maybe these wires are out of order?

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Vladimir · Aug 16, 2026

All the wiring looks factory. Can you take a clear pic of the black box with connectors going in?

. Those yellow wires are for your thermo and compressor temp switch, we will need to check resistance to see if they go through and make circuit, I believe thermo should be 5-10k ohms.

Also when you jumped power to the clutch, you bridged the relay between 87 and 30 correct? Refresh my memory

cswindel · Aug 16, 2026

Yeah I can try to and yes when I jumped it the clutch clicked

Let me know if this is sufficient

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Vladimir · Aug 16, 2026

Ok. Still waiting on that pic. Also yellow red and yellow black on that plug should be going to your thermo fin sensor on your HVAC/evaporator housing. Check for resistance between those pins should be 5-10k ohms or somewhere close. Lmk

cswindel · Aug 16, 2026

Oh the other connector too? Sorry I thought it was just the larger one

cswindel · Aug 16, 2026

Resistance reading and connector

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Also, pressure has been pretty consistent in around this area. As it gets hotter it tends to get higher of course whether it be after car ran or ambient temps

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Vladimir · Aug 16, 2026

If the weather by you around 80f 3.5k ohms should be fine. Also we verified that you Thermo fin goes into your black box and is not damaged.

Now we need to verify power going in and out of your black box. Follow this preview steps. I labeled what the wires on that connector should be

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Pressure is fine. The system is pretty sealed still and is enough for the duel pressure switch to allow relay to energize and clutch to kick once we verify why you get no power at the switch

cswindel · Aug 16, 2026

Ambient temp currently is 98f. Gets into triple digits. Im in the desert is CA haha

Okay so blue wires are both expected to see 12v and both black wires are their associated grounds

Vladimir · Aug 16, 2026

cswindel said:
Ambient temp currently is 98f. Gets into triple digits. Im in the desert is CA haha

Makes sense why it's so low on resistance

cswindel said:
Okay so blue wires are both expected to see 12v and both black wires are their associated grounds

Yes. With all the A/c setting turned on as described and car idling (you can try ignition ON, only first)

cswindel · Aug 16, 2026

With ignition ON and engine NOT running

Blue-Brown stripe

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Blue-Black stripe

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Green-orange stripe

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Ground 1

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Ground 2

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Vladimir · Aug 16, 2026

Not sure how you checked those 2 black ground wires. Put your multimeter to continuity/resistance and verify there is no resistance to chassis ground chassis ground ( any metal part of the chassis). Those 2 black are constant ground.

That green and orange is our main suspect now. We have to see why it's not getting 12v. I gotta look at the diagrams, I'll get back. I gotta kick my kid out of the house, I'll drop him off to his mom's house. About an hour.

Mean while check that ground to chassis and gently take off the black box and crack it open without breaking it. There should be no corrosion onside

cswindel · Aug 16, 2026

Ground resistance. No power or ignition

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Vladimir · Aug 16, 2026

That's a high resistance to chassis grounds, can you see where the 2 black connect to the chassis?

cswindel · Aug 16, 2026

Whats this high and low dial?

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I have no idea where the grounds go. Just feeds into the harness the snakes under the top side of the dash

Looks pretty darn good

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Resolved 2G A/C system not working

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