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1990 Ls400 A/c Electrical Problem


tenchu
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I just picked up a 90 LS400 that the AC doesn't work on.

I took it to an AC shop, and they said that the A/C system looks mechanically sound (compressor, lines, etc) and that there is refrigerant in the lines, but that there is an electrical problem that is not telling the compressor to engage. The AC button lights up, and the blower motor works.

This shop said they don't work with electrical issues so I would have to take it to another shop. I can do electrical stuff, I just don't have the proper tools to work with A/C which is why I took it in.

Is there any common problems with the A/C in these cars that I should know about, or does anyone have and ideas on where I should start?

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It sounds like maybe the compressor clutch is not working correctly. Are you inclined enough to try connecting it directly to the battery and see if it engages/clicks?

I have never done it on an LS, but did on a family member's Hyundai by unplugging the compressor clutch connector and using some alligator clips/wire to connect it directly to the battery.

That should tell you if your car actually has some kind of electrical problem or if it is just a faulty compressor clutch.

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It sounds like maybe the compressor clutch is not working correctly. Are you inclined enough to try connecting it directly to the battery and see if it engages/clicks?

I have never done it on an LS, but did on a family member's Hyundai by unplugging the compressor clutch connector and using some alligator clips/wire to connect it directly to the battery.

That should tell you if your car actually has some kind of electrical problem or if it is just a faulty compressor clutch.

I already figured it out, it was just low on refrigerant, apparently they weren't the smartest A/C shop

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It sounds like maybe the compressor clutch is not working correctly. Are you inclined enough to try connecting it directly to the battery and see if it engages/clicks?

I have never done it on an LS, but did on a family member's Hyundai by unplugging the compressor clutch connector and using some alligator clips/wire to connect it directly to the battery.

That should tell you if your car actually has some kind of electrical problem or if it is just a faulty compressor clutch.

The LS has a compressor rotation rate sensor and if the compressor is enabled and not turning cognizant with engine RPM the dash A/C light will begin flashing. The A/C light can be on constantly but the compressor not running for several reasons. First, the refrigerant pressure sensor is indciating too low refrigerant, pressure too low, or pressure too high. Obviously a failure of the hi/lo switch itself could result in this situation. WOT condition, I don't remember if the TPS is used for this or an actual mechanical switch is used to detect WOT. The engine coolant temperature rising close to the point of overheating will also disable the compressor. The LS engine coolant temperature sensor is prone to failure.

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