Regarding my issue
2):
Quote:
Originally Posted by kuehl
4) If you suspect the low-high binary switch is not allowing the compressor to turn on, you test that by disconnecting the wire between the compressor clutch and the PS and check for voltage and then check for voltage at the original AC power wire that leads to the PS. Pressures switches, like TEV's, are subject to issues when there is contamination in the system as well, or when low voltage levels pit their contact points.
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Didn't see your post last night, but set up a test last night after reading the Bentley manual, ran a trial run to double check measurements while I knew the AC was working, and checked them again this morning.
Conditions/tests last night:
- A/C had been functioning normally on drive home.
- Car not running, but ignition turned.
- A/C cabin fan set to max speed.
- A/C temperature set to lowest.
- Confirmed front condenser fan functioning.
- Indicated ~12v on wire leading to high/low pressure switch.
- Indicated ~12v on wire leading from high/low pressure switch.
- Turned car over, A/C still functioning.
Conditions/tests this morning:
- Overnight low of 64oF.
- Tested at indicated ambient of 72oF.
- Car not running, but ignition turned.
- A/C cabin fan set to max speed.
- A/C temperature set to lowest.
- Confirmed front condenser fan functioning.
- Indicated ~12v on wire leading to high/low pressure switch.
- Indicated 0v on wire leading from high/low pressure switch.
- Indicated zero continuity across pressure switch leads.
- Indicated 75 PSI static high-side pressure.
- Turned car over, AC non-functioning.
- A/C turned on ~10 minutes into morning drive.
So, that's one issue diagnosed. a bad/failing high/low pressure switch. I'll probably be giving you a call within the next week or two, Charlie, to get a replacement switch. I'm currently in the process of relocating to the Atlanta area, so something that requires evacuating and recharging the A/C system will have to wait.
Regarding
1):
Quote:
Originally Posted by kuehl
2) What is missing in your data above is what you had 2 years ago: How much refrigerant, and what the low and high side pressures were at idle at a given ambient temperature. Look up your records from when you charged the system 2 years ago. Without those 2 year old data points you could have been overcharged 2 years ago.
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I didn't do the work myself (otherwise I'd remember the pressures, at least vaguely); mechanic mentioned above did. I'll see if I can grab them, but wouldn't put much faith in it. Additionally, considering it hasn't been serviced since, if pressures are high now I'd assume pressures were high then.
Quote:
Originally Posted by kuehl
3) If you are seeing 30 to 40 psi on the low side I would not point to the TEV (expansion valve) yet. Most new TEV's do not fail because of a mechanical defect in the TEV, rather failure is more related to moisture in the system or debris in the system getting in the TEV. Seeing 30-40 psi on the low side while operating says your TEV is opening and most likely throttling (the valve opening moving with demand). If the valve was closed you'd have 0 to - low side pressures. If the TEV was stuck open you might have have pressures higher than 40 or it might suggest you are overcharged or have air in the system. A stock 1988 takes about 47 oz of R12 and anywhere from 80 to 90% of that 47oz in R134a. If you had much less of either refrigerant in the system and you noted 350 psi on the high you could have air in the system.
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Your and my thinking is in the same spot. I think it has air in the system and is in need of a full evacuation, especially after reading the Sanden diagnosis guide (linked above). That should hopefully happen at the same time I get the pressure switch replaced.
I'll follow up when I have more progress to report.
Thanks again.