Troubleshooting the air conditioning in my 98 Lumina. Using Torque Pro and a custom PID set, I finally managed to pull AC telemetry from the PCM:
- AC Request responds to cabin controls (okay good, that rules out quite a lot of wiring)
- AC High Side Pressure is 0.22V ~= 6.96PSI (Ouch. If that’s not relative to ambient, the sensor or wiring harness is DEFINITELY toast)
- AC Pressure Out of Range is on (no shit?)
- AC Relay is off (again, duh)
That narrows it down to three possibilities:
- wiring fault between PCM, AC pressure sensor, and/or ground
- faulty sensor
- or simply no charge in the system.
(Well, it could be a PCM fault, but the chances of that are pretty damn low.) My gut says the sensor is blown open, that reading seems absurdly low for it to simply have leaked away to nothing. Either way, I think I should verify the wiring harness first.
Right now, I definitely will:
- With key in RUN (so OBD port is active), engine off, AC Request OFF (fan speed in position 0 should do it), jumper AC high pressure sensor connector, 5V to sense wire. If reading doesn’t change to ~450PSI, wiring problem.
- Under same conditions, measure voltage between 5V and ground on the same connector. If not at 5V +/- 0.2V ish, wiring problem.
Either of those, I’ll definitely fix myself. It’s electrical, it’s what I know.
Otherwise… I have an idea, stop me if this is stupid.
I have half a mind to give it just enough charge to run, so the leaks weep, and go at it with UV dye, spot fix from there. But, pretty much every recharge kit on the rack mixes in a “stop leak” clogging agent. Circulating that kind of material through the entire system strikes me as a catastrophically bad idea, and from what I’ve seen, most mechanics agree. So, is it possible to get a can of premixed 134a + oil that does NOT include that garbage? Or should I not be adding oil and just use a refrigerant only can? I spotted a few of those, I’d have to get the gauge/hookups separately but that shouldn’t be a problem.
And to charge it, I’d need a pressure gauge anyway, so I might as well first see if the gauge reading matches the sensor. I’m not trying that swap myself though. I know it’d have to be evacuated and I’d never be able to get the equipment for that. That’ll be a shop visit.