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Old 06-26-2017, 08:30 AM   #1
PolarBear
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AC not being commanded

I swapped my car to an LR4 and I wired it like the 99 F-car for the AC. So when you apply 12VDC to R17 it should bring pin R34 (I may be getting the numbers wrong since I don't have the book in front of me) low to enable the relay. If I jump the wires at the relay to work the compressor (I have the wire split for the compressor to go back to the ECM for compressor status) the compressor comes on and fan 2 comes on, as it should.

This ECM was for the LR4, but I re-flashed it to a 2002 manual Camaro tune, so the tune should match how it is wired.

Anyone have any ideas? I double checked that I am getting 12VDC to the request pin and all the other wiring for the relay.

Last edited by PolarBear; 06-26-2017 at 08:31 AM.
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Old 06-26-2017, 10:16 AM   #2
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Did you try jumping the pressure sensor/switch?

I think its pin 43, not 34, for relay ground from pcm. And you don't have the ground signal, correct?

Quote:
When the vehicle operator makes an A/C request, a 12 volt request signal is sent out over the A/C request signal circuit and grounded through the PCM. When this request signal is grounded, the PCM can activate the A/C compressor clutch.

The PCM turns on the A/C compressor clutch by providing a path to ground through the A/C compressor clutch relay control circuit for the A/C compressor clutch relay. Power is provided to the A/C compressor clutch relay from of the underhood fuse block on the ignition 1 voltage circuit. Once the relay closes its internal switch, power from the battery is provided to the A/C compressor clutch through the A/C compressor clutch supply voltage circuit. Whenever the compressor is turned off, the A/C compressor clutch diode prevents a voltage spike from entering the vehicles electrical system. The ground circuit provides a path to ground for the compressor. The A/C compressor clutch relay control circuit is grounded internally within the PCM. On vehicles with the V8 option, an A/C compressor clutch status signal is sent to the PCM on the A/C compressor clutch supply voltage circuit.

The PCM will engage the A/C compressor clutch any time the engine speed is below 5000 RPM and the A/C is requested unless any of the wing conditions exist:

Throttle angle is at 100 percent (WOT).
Vehicle launch, hard acceleration from a stop.
Idle quality
The A/C refrigerant pressure sensor is above 2826 kPa (410 psi ) or is less than 207 kPa (30 psi ).
Engine speed is more than 5500 RPM .
Engine coolant temperature (ECT) is more than 121°C (250°F) for the L36 and 125°C (257°F) for the LS1.
Transmission shift
Engine torque load
Top of travel clutch switch position, if equipped
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Old 06-26-2017, 11:45 AM   #3
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Quote:
Originally Posted by sweetbmxrider View Post
Did you try jumping the pressure sensor/switch?

I think its pin 43, not 34, for relay ground from pcm. And you don't have the ground signal, correct?
You mean jump the 5 volt reference to the signal input to the ECM? I tested the 5VDC, ground continuity, and the output of the sensor. I put my meter on the output, and I put compressed air into the AC system and watched the output of the sensor rise, then when I jumped the relay and forced the compressor I could see the voltage rise again.

When I have the 12VDC on the request pin I do not have ground continuity on pin 43 for the relay.
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Old 06-26-2017, 12:19 PM   #4
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Nah I meant unplug the sensor and jump with paperclip. Is the system charged?
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Old 06-26-2017, 12:27 PM   #5
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Quote:
Originally Posted by sweetbmxrider View Post
Nah I meant unplug the sensor and jump with paperclip. Is the system charged?
I Understand that, but jump what?

System isn't charged yet, I wanted to make sure it worked before I brought it to Josh. I basically equalized to the ~110psi of the compressor, so it should mimic being "charged", no?
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Old 06-26-2017, 01:01 PM   #6
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Jump the plug of the low side switch. That way low side isn't seeing too low of a pressure and preventing compressor from engaging.

I've never done what you are attempting, I'd say grab a can or two of over the counter stuff but you are r12 so that won't work. If the low side switch is bypassed, you shouldn't have to worry about having enough psi to fool system and you won't have to worry about high side hitting cutoff obviously.
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Old 06-26-2017, 01:10 PM   #7
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I guess I see where you're going. 4th gens only have one switch though, on the high side. But maybe I am not getting enough compressed air into the system to hit that 30PSI mark.I wish I knew what the actual mV readings were. I guess this new aftermarket switch I bought could be a POS right out of the box.
That was my thought too that the system needs to see some pressure before it will kick on.
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Old 06-26-2017, 01:21 PM   #8
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Oh wait, its only one and its a sensor? Because my cliff notes say, "The A/C refrigerant pressure sensor is above 2826 kPa (410 psi ) or is less than 207 kPa (30 psi )." so its not as simple bypass and fool. I think you should just charge it
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Old 06-26-2017, 01:24 PM   #9
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Quote:
Originally Posted by sweetbmxrider View Post
Oh wait, its only one and its a sensor? Because my cliff notes say, "The A/C refrigerant pressure sensor is above 2826 kPa (410 psi ) or is less than 207 kPa (30 psi )." so its not as simple bypass and fool. I think you should just charge it
Yeah, that's why I didn't know what you wanted, lol. It sees progressive voltage
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Old 06-26-2017, 01:26 PM   #10
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This does bring me into my next question, my reverse lockout isn't being commanded by the ECM either, I mean I don't think it is. I am getting an error code for it, and I haven't gotten under the car to make sure I have 12VDC at the solenoid. The fuse I added looked fine, so I don't think that's it.
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Old 06-26-2017, 07:30 PM   #11
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Looks like stock the fuse is hot in run and start, feeds one side of noid, pin 44 c2 grounds internally in pcm. Maybe rig up a switch and try manually operating it?
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Old 06-26-2017, 07:38 PM   #12
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charging it seems to be the best bet lol
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Old 06-27-2017, 07:44 AM   #13
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Quote:
Originally Posted by sweetbmxrider View Post
Looks like stock the fuse is hot in run and start, feeds one side of noid, pin 44 c2 grounds internally in pcm. Maybe rig up a switch and try manually operating it?
I COULD, but I don't really wanna, lol. When I put the car in the air for the oil change I was going to look at it. I have to do my "new parts" fluid changes already. Put over a thousand miles on it now
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Old 07-03-2017, 12:30 PM   #14
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Over here at JSP. Looks like I connected the wire to command the AC to the wrong wire on the HVAC controls. Disconnected the wire from the connector and jumped it to+12vdc and the AC was commanded as it should be!
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Old 07-03-2017, 09:23 PM   #15
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Nice man!
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