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Old 05-19-2017, 09:39 PM   #31
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Good news & good work!

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Old 05-19-2017, 10:45 PM
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Thank you, RUBI 4 MY MRS for your patient and expert guidance. I would not have figured it out without your help. Instead, I probably would have replaced the compressor and spent a fortune throwing parts at it. Or worse: Give up and take it to a shop!

I'll report back (hopefully tomorrow) once the VCG job is done and I can run the engine to confirm A/C operation.

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Old 05-20-2017, 06:44 PM
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Just call me Frosty.

A/C is nice and cold. I can't thank you enough, RUBI 4 MY MRS. You sent me down the right path to finding the problem and prevented me from going on a wild goose chase.
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Old 05-20-2017, 08:32 PM   #34
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This needs to be in the Sticky section for future reference.. EXCELLENT tech advice there Sir (Rubi4myMrs.) Now I'm going out to do some of the same diagnostics on mine..
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Old 01-17-2020, 06:18 PM   #35
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My turn to bang my head against the wall, hopefully it'll cave.. Been trying to get my AC working for a while now, it's topped up (continuity in both the pressure switches).

If I jump the compressor from the 12V by battery it will engage and stay engaged. When I insert the relay (tried the horn's too) it clicks, engage the clutch for a split second, then disengages.
I measure 12V in 30, 85 on the relay socket, 87 has 170 ohm to ground and 86 has 0 ohm to ground.
If I jump 30 and 87 the clutch will not engage, but I'm seeing 12V at 30, and I get it to engage if I jump 87 from the battery. Not enough juice at 30 to keep it on?

Does anyone have any bright ideas to why this might happen, have checked all the fuses named here.
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Old 01-17-2020, 07:12 PM   #36
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What year?
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Old 01-18-2020, 03:42 AM   #37
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Originally Posted by RUBI 4 MY MRS View Post
What year?
Sorry I left that detail out! It's a 98 4.0 automatic (US).
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Old 01-18-2020, 02:09 PM   #38
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OK so the fuse feeding the relay terminal 30 is fuse 11 (40a) in the PDC.

Make sure when you jump 30 to 87 you are getting good contact to both terminals with the jumper to ensure the compressor is getting proper power from 30.

If you think terminal 30 is “lacking power” the best way to check that is to use a 12v test light rather than a meter since the meter will give the voltage reading even if the power (amperage) is almost 0. See if the light is as bright at 30 as it is when checked at the battery posts. If low at 30 make sure there is no corrosion at the terminal & if good there you may need to lift the PDC & check the connection at the fuse input (power) leg.

Also check the fuse for continuity just to be sure it is good.


When you checked for continuity (or resistance) at 87 to ground you are getting the resistance of the compressor clutch magnetic windings so resistance there is normal to have. I don’t know what the reading should be but will assume the 170 you got is OK.

If you had continuity through 86 to ground when the key was on & switched to a/c that tells you the PCM is doing its job & the pressure switches are closed too.

If the compressor is kicking in, then out very quickly (with relay in) that is telling you something is not right. Usually the refrigerant is low causing the low pressure switch to open when the compressor comes on & draws the low side down too far for the amount of refrigerant in the system.

Some cycling is normal but not rapid or very frequently.

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