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Hey all,
Finally getting back to working on the mysterious A/C & ECU woes on the '89 900S. I got her going today after installing new AMM (thanks to Jim at SobStory and everyone here for the diagnosis), but still no A/C. To summarize, she now has a good used #564 ECU from GregD, new AMM, runs good again, but A/C compressor doesn't click on when summoned. One cooling fan only. I ran a bunch of electrical checks today, per KeithG's suggestions, and a procedure at Swedish Wrench (see http://www.swedishwrench.com/ACdiag/ACdiag1.htm). Here's the results:
- All fuses good. Checked continuity on every single one just to be sure.
- Got freon. No bubbles. Jumped low pressure switch and compressor still didn't click on.
- No voltage at compressor wire. Also no voltage at high temp switch in the coolant line.
- Jump pins 30 and 87b on the A/C relay, and compressor clicks on. So high temp switch should be good, and compressor not getting voltage.
- A/C RELAY CHECKS
- 12v at pin 15
- Ground at pin 50 while running (didn't have someone to crank, so didn't check it for 12v while cranking)
- 12v at pin 86 (should be through low pressure and anti-frost switches)
- 12v at pin 30
- continuity between pin 87 and 85a on cooling fan relay
- continuity between pin 87b and compressor
- Ground at pin 31
- 12v at pin TK
- ~4v at pin 16
So it seems we've shown all the cutoff switches good, and all the relay pins read as they're supposed to. Compressor comes on if you give it voltage directly, but it won't come on normally.
I also did independent checks (per Bentley) for the high temp cutoff switch, the low pressure switch, and the throttle position switch. All passed normally. I couldn't get readily at the anti-frost switch, so I suppose that remains still somewhat suspect, although according to Swedish Wrench, it should be good since we've got voltage at pin 86.
Other clue is that the second cooling fan doesn't come on.
Maybe the compressor diode, or the A/C relay is bad?
Again, this happened apparently coincidentally after diagnosing a bad ECU, replacing initially with a #580 (didn't work), then with an '88 900S version (don't recall the #, worked, but no A/C), then alas with an '89 900S #564 (which worked, save the bad AMM symptoms).
The gremlins must die!!!
'Roo
'89 900S
'01 9-3SE
posted by 128.42.176...
, Mon, 7 Oct 2002 15:27:39
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