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AC relay??
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Posted by JimBlake [Email] (#141) [Profile/Gallery] (more from JimBlake) on Mon, 7 Oct 2002 15:27:39 Share Post by Email
In Reply to: '89 900S A/C Electrical Gremlins, Mr. Science, Fri, 4 Oct 2002 19:09:27
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You get 12v at pin 86; this means your AC switch is turned on, and the low-pressure & anti-frost switches are satisfied. I think(?) the 'anti-frost' switch is what cycles the compressor during normal operation.

You have ground at pin 31; unless maybe the ground is dirty. Maybe it looks like a ground to your DVM, but when it has to sink a little more current, it's not such a good ground... Check that out.

Check out pin 50 while cranking. I guess that's the signal to start the 10 second delay. Maybe the relay 'thinks' the car's not running yet.

Pin TK is for the throttle switch. That switch grounds this pin to tell the AC to turn off at wide-open throttle.

Pin 16 is an output. It's supposed to tell the FI ECU to open the AIC valve to compensate for the AC load. It actually leads the compressor by a small delay, & it shouldn't keep the AC from running. This changed between '88 & '89.

When you jumper 30 to 87b on the AC relay, the compressor comes on. This means the compressor diode is OK, along with the high-temperature switch. This is what the relay is supposed to do for you. If it was working properly.

If you were to take out the AC relay, & make a jumper to connect the slots for 30, 87, & 87b all together, your compressor & fans should run continuously, without cycling like they should. Do this just for diagnosis, not a permanent fix.

If you don't find the troubles I mentioned at pin 31 or 50, it looks like your AC relay is bad.


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