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Old 06-22-2022, 08:00 PM   #1
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2002 SL
Default No A/C? A/C Button Circuit?

Okay, I'll start by saying that the vehicle in question is a 2002 Saturn SL SOHC.

I recently replaced both the cluster lights and the HVAC control head lights with LEDs, using drop in replacements for the cluster and desoldering and soldering in new LED's with resistors into the HVAC control head. The lights work perfectly but now my A/C won't turn on.

I'm trying to troubleshoot the circuit, assuming that something I did by being in there is causing the problem, and I'd like to verify some information if I could.
According to the OE wiring diagram, the A/C button is wired in series with the A/C pressure switch. The A/C button receives power only when the blower motor is on, and from the switch the power goes out to the LED indicator and then to one side of the pressure switch.

Then it goes to the BCM which tells the PCM via the Class II data network to ground the coil side of the A/C relay and engage the compressor clutch. My question is, and I think it's obvious but I'm just confirming, is "Should there be 12 volts on the one side of the A/C pressure switch with the A/C button pressed? According to what I can see in the diagram, it should be, as it flows directly from the fan, through the A/C switch and LED and to the pressure switch. I'm asking because I don't see 12 volts on that wire with the A/C button on, either backprobed or with the connector unplugged. It shows 0.4 volts with the button off, 0.7 with the button pressed, voltmeter hooked to battery ground, and approx. 0.6 volts on the signal wire on the relay with the voltmeter hooked to battery positive.

Am I missing something or is the problem obvious? My next step was to pull the dash apart again and check at the HVAC control head connector that battery voltage was getting to the A/C switch, but not getting out of it. I feel that's were the problem lies, but I could be getting "tunnel vision" because of the recent work I did. I can manually engage the A/C via jumping pins 87 and 30 on the AC relay, so I know that side of the circuit is good. I also swapped the AC and horn relays and confirmed that the relay wasn't at fault. The AC and HVAC fuses are both good, and the recirc, blower motor and rear defroster all work, just not the A/C button.

Any help would be greatly appreciated!!!
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Old 06-22-2022, 09:37 PM   #2
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2003 L-Series 3.0L Sedan
Default Re: No A/C? A/C Button Circuit?

There are several ways of diagnosing/troubleshooting ac problems; examining wiring diagrams with full knowledge of how ac circuits operate under normal conditions then troubleshooting circuits, testing the ac system bypassing the pressure switch, knowing if the pressurized system leaked with either a uv blacklight or familiarity with refrigeration gauges and running the compressor to measure pressures. Be aware that bypassing the ac pressure switch only checks compressor operation. No assumptions can be made whether or not the system leaked refrigerant where the low pressure switch detected loss of refrigerant (below 40 psi without running the compressor). If a system leaked with pressures below 40 psi, the pressure switch sends a signal to the pcm to disable compressor operation until repairs are made for the system to hold pressure. Standby pressures can vary from 70 psi to 95 psi.

Can you post the wiring diagram?
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