A/C Wiring Errors
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Joined: Apr 2010
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A/C Wiring Errors
I have a 87 where the compressor clutch will not engage. I followed the troubleshooting directions in the SM. When measuring the voltage, specifically at the Blower Control Module, and the connection from the HVAC control to the ECM, the voltages are all wrong. When they are suppose to be 12V, they are 6-7V or 0V. And when they are supposed to be 5-6V, they are 11V or 0V. I replaced the HVAC control (C68 Electronic control) with another one with the same voltage readings results. It is like the SM is incorrect. I suspect the Blower Control Module in that someone cut the surge diode off across the clutch. Any ideas? Thanks.
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Most don't engage because they're out of gas - Did you check the Charge?
I remember a Bulletin changing the voltages (because they were wrong), but I don't think you have a Control Panel issue with a new or rebuilt one.
Early Electronic Controls have 3 circuits: 1. A/c request to the Module to switch on Clutch Coil Ground. That will only be sent if: 2nd Circuit through the High Limit and Low Pressure Switch is closed AND if a third Circuit is grounded at the ECM.
Verify that there's 12 volts (from the a/c) fuse at the Clutch Coil with the key in run (it doesn't matter if a/c is requested). Jumper the Module side to ground and the Clutch should engage. Verify that the High Limit and Low Pressure switch contacts are closed. If the High is open, replace it. If the Low is open it's probably out of gas. Verify 6 volts at the ECM Pin B6.
For the Module, verify it's got power from the fusible link at the Starter - red wire. With the engine running and a/c requested, Module signal should have a small voltage that rises to allmost ignition with the harness disconnected. If not there, the wire is open, or one of the Circuits aren't completed (again, probably because it's out of gas). If it is there and the clutch doesn't engage, replace the Blower Module.
I remember a Bulletin changing the voltages (because they were wrong), but I don't think you have a Control Panel issue with a new or rebuilt one.
Early Electronic Controls have 3 circuits: 1. A/c request to the Module to switch on Clutch Coil Ground. That will only be sent if: 2nd Circuit through the High Limit and Low Pressure Switch is closed AND if a third Circuit is grounded at the ECM.
Verify that there's 12 volts (from the a/c) fuse at the Clutch Coil with the key in run (it doesn't matter if a/c is requested). Jumper the Module side to ground and the Clutch should engage. Verify that the High Limit and Low Pressure switch contacts are closed. If the High is open, replace it. If the Low is open it's probably out of gas. Verify 6 volts at the ECM Pin B6.
For the Module, verify it's got power from the fusible link at the Starter - red wire. With the engine running and a/c requested, Module signal should have a small voltage that rises to allmost ignition with the harness disconnected. If not there, the wire is open, or one of the Circuits aren't completed (again, probably because it's out of gas). If it is there and the clutch doesn't engage, replace the Blower Module.
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I appreciate the response. The high limit and the low pressure switches are closed, and go to ground. All the voltages to the Blower control module are correct, including the one from the A/C control. That voltage is about 7V connected, and about 11V disconnected. On my car, the connection to the ECM is C6, not B6 (B6 goes to the VATS module). It is 6.5V when A/C is requested, and 0V on ECON. Based on this info, it appears the Blower control module is defective. Do you agree? Thanks again.
Race Director
Joined: Apr 2002
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From: Anaheim CA
The ECM (Engine Control Module) input for the A/C request is on pin B8. This pin tells the ECM that the compressor is engaged so it can raise the idle to compensate for the added load on the engine. Pin C6 is one of the IAC output pins.
The CCM (Climate Control Module) and ECM both operate on 5 volts internally, so that's generally the voltage you see on outputs and pulled-up inputs that are open.
I assume you're in section 8A-64-xx of the FSM for troubleshooting...
The CCM (Climate Control Module) and ECM both operate on 5 volts internally, so that's generally the voltage you see on outputs and pulled-up inputs that are open.
I assume you're in section 8A-64-xx of the FSM for troubleshooting...
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I did jumper the clutch (black wire on the Blower control 4 pin plug) to ground, and the clutch does engage. In my SM, 8-64 is the manual control (C60), where 8-67 in the auto system (C68) like I have. Based on all our your assistance, I'll order the blower control module. Thanks for all you help.
