Compressor fan running without engine on

BLESSING EWOBOR

MEMBER
2003 LEXUS RX 330
6 CYL
2WD
AUTOMATIC
109,675 MILES

Hi, I am working with the vehicle listed above. The compressor fan runs on its own without the engine on or compressor engaged. When the key is turned to "run" position, without the engine running and not engaging the compressor, the compressor fan starts to run. I have tested the necessary fuse and relay, if there is any short to ground or power, they are all working properly. What could be the cause? I don't know if I can get the circuit diagram, the compressor fan only stops working when I disconnected it as shown below.

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4 Replies

AL514

MECHANIC
4,125 POSTS

Hello, that box is the relay box for the fans, here's a diagram of that circuit (picture 1). So either that relay is stuck on if you see how it works, the condenser fan has 2 relays it needs to go threw to work. Fan relay #3 first, then grounds threw fan relay #2, the ECM grounds all 3 fan relays. Now I've seen a bad ECM ground cause the fan to stay on all these time too, it's a default strategy so if the ECM fails the car won't overheat. The 2nd pic is the ECM grounds, they're all white/black wires, labeled E01-E05 at the ECM connector. These should be checked.

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Saturday, September 5th, 2020 AT 9:10 AM

BLESSING EWOBOR

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663 POSTS

Thank you, for the first picture, it has single pressure switch while the vehicle I am working with has 4 wires. The second picture is somehow blur, I don't know if I can get a clearer one. Please could I have the diagram that link both the ECM and the fans together.

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Saturday, September 5th, 2020 AT 9:17 PM

AL514

MECHANIC
4,125 POSTS

This is the tie in between the ECM and 3 fan relays, the small green box at the bottom of the picture. The light green/black wire and the red/white wire. The 3rd picture is the ECM grounds, there's 5 all white/black wires. The pressure switch probably shares a reference voltage with other sensors and/or ground wires, that's what that seems to be. It's possible that the box you're unplugging is shorted inside and sending power or giving ground to the relay circuit.

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