No A/C - need ideas

lee · #1 04-09-2002, 07:17 PM

1992 LS-L - I've owned for a couple of weeks...

I have tried to diagnose my A/C system and am out of ideas. Here's what I know/have done:

1. Fuses and wires to compressor relay have continuity and power is at the correct leads. Compressor will not kick in without jumping it.
2. According to AllData, The WB wire from the ECU to the relay (pin #8, connector B60) is supposed to be at battery level when the ECU wants the compressor off, and go to ground when it wants the compressor on (but it never goes to ground). If I disconnect the WB wire from ECU to the relay, and use a jumper to ground the relay the compressor kicks in - so relay and other wiring is OK, but bought and tested another relay just to be sure)
3. Security system and cigarette lighter not working, but everything else (beside A/C) is now working fine (including visor vanity lights). Engine/transmission performance is good (20 mpg around town). No blinking dash lights, no stored codes on those things I can retrieve at home.
4. Hi/Low sides of A/C compressor test within limits, passed professional leak test, previously converted to R-134, no R-12 present.
5. No errors on climate control internal diagnostic routine. Climate system responds correctly in every way except to turn on compressor, i.e., heat, defroster, door actuators (where air blows out top/bottom), ambient sensor, sunload sensor, etc. all work properly.
6. ECU gets proper voltage signal from climate unit - battery level when A/C should be on, no signal when A/C should be off.
7. Throttle position sensor, trinary switch, water temp sensor, all working properly.
8. ECU turns on fans at radiator (jumper the trinary and it even correctly turns them up a notch), and the climate system sets interior fan speed correctly based on difference between dash setting and interior temp (higher fan speed if there's a large difference).
9. Have tried removing battery leads and touching them together, also tried leaving them off overnight. Removed ECU connector and reseated.
10 Didn't test evaporator or refrierant sensor, but as I said Climate control module is sending correct signals to the ECU when the A/C should be on or off.

Have run out of ideas except replacing the ECU.

Ideas (any) solicited.

Want to gain good karma? Have a spare ECU that correctly controls the A/C (even if it has some other problem) so I could test my system. I'll gladly pay to/from postage. Replacing the ECU is simply too big an expense just to find out the problem is somewhere I've overlooked. I live in Florida, and 4/60 works for now, but the temps (and my frustration) are rising.

tia, lee

Seraph · #2 04-09-2002, 08:23 PM

If you ran 60/4 or 4/60, it will cool you down. I'll crank out some ideas on this in a bit. Worst case, I'll sell you my AC unit -- It comes attached to a 94L though. Cost: for you, 3500

Lwin

Beav · #3 04-09-2002, 10:05 PM

I'd install a temporary switch to the relay until I ran across a 'known good' ECU for testing. Might as well chill while waiting...

mohrds · #4 04-10-2002, 06:30 AM

Wow! Very Thurough diagnosis. Everytime I thought to myself "Oh, try this" you listed it in the next section.

I agree that it is possibly the ECU. Or it could be that the ECU is kicking the AC out because of another sensor.

What kicks out the AC? That I don't know for sure. I'm pretty sure that when you floor it the AC kicks out. That may be from the TCU sending a power mode signal to the ECU? I assume there are other things that would cut out the AC, High Engine temp, limp home mode, etc.

Doug