89 With No AC Cutch Control
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Instructor
Joined: Apr 2010
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From: MD
89 With No AC Cutch Control
I'm about at my whits end trying to diagnose my AC problem. When I bought the car the wires to the AC clutch were cut. I repaired them and now I'm here. I have the electronic climate control on my car. All features of the heat/AC work except the AC compressor. I've done the diagnostics on the control head and have no codes. (Heat, Blend Door, Fan, everything works normally) I've hooked up the scanner and monitored the AC command for the ECM. It shows YES when I turn on the Auto at 60 degrees. The engine idles up as it should and the blower motor runs on high. (Outside temp around 85) I'm just not getting a ground on the green wire at the AC clutch. I have 12 volts on the BL/W wire and the system was just charged yesterday to make sure. I've jumped all switches and there is no change. Still no ground. If I manually ground the AC clutch the compressor runs and is cold as he**. It just cant be regulated. Any ideas??? And possible component locations? Thanks in advance.
Le Mans Master
Joined: Aug 2000
Posts: 8,838
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From: Australia
Blower control module located in the A/c ducting on firewall that controls blower speed also operates the compressor clutch by putting wire to ground.
Are you getting clutch on signal from head unit to BCM? (IIRC 8 Volts )
If so, possible BCM is faulty on clutch control circuitry
Are you getting clutch on signal from head unit to BCM? (IIRC 8 Volts )
If so, possible BCM is faulty on clutch control circuitry
Last edited by rodj; Jul 2, 2010 at 11:19 AM.
Thread Starter
Instructor
Joined: Apr 2010
Posts: 114
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From: MD
Blower control module located in the A/c ducting on firewall that controls blower speed also operates the compressor clutch by putting wire to ground.
Are you getting clutch on signal from head unit to BCM? (IIRC 8 Volts )
If so, possible BCM is faulty on clutch control circuitry
Are you getting clutch on signal from head unit to BCM? (IIRC 8 Volts )
If so, possible BCM is faulty on clutch control circuitry
I've got 12 volts at the Green/Yellow wire on the Blower control module. Is that the correct one?
Le Mans Master
Joined: Aug 2000
Posts: 8,838
Likes: 31
From: Australia
Will have to look at FSM when I get home.
Was helping someone with similar problem and recall the trigger for clutch operation was voltage dropping to BCM from 12 to 8V
Was helping someone with similar problem and recall the trigger for clutch operation was voltage dropping to BCM from 12 to 8V
Last edited by rodj; Jul 2, 2010 at 07:52 PM.
Melting Slicks
Joined: Aug 1999
Posts: 2,240
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From: Baltimore, MD USA
12 volts on the Green/Yellow wire indicates the HVAC Control Head is requesting the Blower Control Module ground the Dark Green wire which completes the Clutch Coil circuit.
Verify the electrical connector pins are making good contact with the Blower Control Module. The module is located inside the evaporator housing.
Here's a picture of the module showing the two electrical plugs where a 4 pin and 2 pin connector plug into it.
On the 2 pin connector is a Red wire which is 12 volts. It's hot at all times to power the Blower Control Module. On the 4 pin connector is a Black wire which is the ground for the module.
Verify the electrical connector pins are making good contact with the Blower Control Module. The module is located inside the evaporator housing.
Here's a picture of the module showing the two electrical plugs where a 4 pin and 2 pin connector plug into it.
On the 2 pin connector is a Red wire which is 12 volts. It's hot at all times to power the Blower Control Module. On the 4 pin connector is a Black wire which is the ground for the module.
Last edited by Hooked on Vettes; Jul 2, 2010 at 08:04 PM.
Thread Starter
Instructor
Joined: Apr 2010
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From: MD
Thanks for the info!!! I've got 12 volts on the Green/Yellow wire and on the Red wire. I'll check the black for ground. When wiring in the diode, I found out I had it backwards. The diode is blown and I'm thinking that I fried the module because of this. Maybe the PO had blown it and thats why the compressor wiring was cut. I'll check the ground before ordering a module and another diode. Thanks again for all of your help.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
Unfortunately, running without the diode can short out the clutch coil. Check resistance across the coil leads - there should be some resistance and not completely open. If it's ok, installing the diode so it only flows to the Module may get it working.
