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Don - Mo Lurch
Don - Mo Lurch, Auto Mech / Electronics
Category: Chevy
Satisfied Customers: 21037
Experience:  Chevrolet Cert., Heavy Line Mech, Race Shop Owner, Mobile Electronics.
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I have a 2007 impala lt 3.9 engine. I am getting a code

Customer Question

I have a 2007 impala lt 3.9 engine. I am getting a code P0645 and my ac compressor is constantly running even when it is aupposed to be off.
Submitted: 1 year ago.
Category: Chevy
Expert:  Don - Mo Lurch replied 1 year ago.

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sorry for the delay............
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Greetings...... “Hi, I’m Don (aka MOLurch) and I look forward to helping you!”
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This is typically caused from a bad compressor clutch relay, bad connections to it or bad PCM
Ignition voltage is supplied directly to the A/C compressor clutch relay. The powertrain control module (PCM) controls the relay by grounding the control circuit through an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line, which is monitored by the PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts . When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage.
The Relay is located in the Under Hood Fuse / Relay Box
I can post the Testing Procedures if you want, but you will need use of GM Scan Tool or Equal
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Customer: replied 1 year ago.

I have a scan tool. Like the one on the link. Will it work? It does read 3 different ac things.

http://www.amazon.com/Launch-Creader-Reader-Automotive-Function/dp/B00EN7JPIO

Expert:  Don - Mo Lurch replied 1 year ago.

according to specs, this will not......
But you can try a reset of the Trouble Codes & see if that clears the issue.

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Customer: replied 1 year ago.

I have tried that. And also disconnecting the battery.

Expert:  Don - Mo Lurch replied 1 year ago.

ok...........

as stated, "typically caused from a bad compressor clutch relay, bad connections to it or bad PCM"
Replace the Relay, clear the codes & try
Otherwise, you will need to Test via correct type Scan Tool

Customer: replied 1 year ago.

My scanner shows ac relay circuit short to ground. I know the relay is good cause I swapped it with another relay. I would like to test the pin holes for the realy...can u tell me if im supposed to have power or ground to each pin hole.

Expert:  Don - Mo Lurch replied 1 year ago.

Here is GM Test procedures:
click attachment below

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The numbers below refer to the step numbers on the diagnostic table.

3.Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands, as necessary.
4.This step tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
5.This step verifies that the PCM is providing ground to the A/C compressor clutch relay.
6.This step tests if ground is constantly being applied to the A/C compressor clutch relay.
7.This step tests for a short to voltage or an open.
13.Perform the programming procedure for the PCM.

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NOTE: Do NOT Rate on how much TIME you waited, because I am not on 24 / 7 and I answer as soon as I see the question.
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If for any reason, you can't rate my answer OKAY, GOOD, or EXCELLENT today.
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Expert:  Don - Mo Lurch replied 1 year ago.

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Hello again Lurch here.

I noticed we have not yet resolved your concern you asked about.

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