Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by azaviator, Jun 25, 2012.
Thanks for all the help Brian!!
That does not look right if we follow the diagram. It appears terminal 85 is the one that goes to the VCM and not teminal 86.
With 0.13V at terminal 85 only means the VCM is providing a ground path for the relay coil. It confirms what you were saying that the relay is always pulled in even with the A/C switch OFF. The VCM is always providing a ground path for the relay at terminal 85. Something is shorted inside the VCM. We need to find out if the climate control is integral to the VCM.
Was the cabin blower running or not when the compressor clutch is engaged?
I think I got the terminals backward because the diagram is a little blurred.
Your voltage measurements are correct. It looks like terminal 85 is the one that is connected to the VCM. With that reading, it only proves that the VCM is constantly providing a ground path for the A/C compressor clutch relay to get pulled in with the ignition ON. the problem is internal to the VCM. There could be a shorted component inside that is providing ground to the relay coil, thus, your A/C compressor clutch is always engaged. We need to find out if the climate controller is integral to the VCM. You have a bad climate controller.
All switches and dials were off on the dash control panel. From what I can tell, the dash control and VCM are seperate. They are connected only by a wire through the L/P switch. My thinking is that the wire from the relay to the VCM is bad. Is there a way to bypass it momentarily to determine if the system works correctly outside of that wire? That would show me if the problem lies with the wire or the VCM.
Pull the relay out of the socket and do a resistance measurement on relay socket terminal 85 to ground. Test your meter by probing one ground post (bare unpainted chassis bolt) to another ground post (another bare, unpainted bolt) in the engine compartment. Compare that reading to your term 85 to ground resitance reading.
With the relay pulled and If you can unplug the connector #3 from the VCM and do another resistance measurement from term 85 of relay socket to ground, that will be the best test for dead short on the said wire.
This will tell you if that wire has a dead short to ground from terminal 85.
Ground to ground gave me 003, 85 to ground gave me nothing, 86 to ground gave 004, 86 to connector on VCM gave 022.
Also, forgot: 85 to VCM connector gives nothing.
Are these readings with the ignition switch OFF, just the relay pulled out and C3 on VCM still connected?
yes to all except C3 on VCM was disconnected. What difference should it make with it connected?
With C3 on VCM disconnected is better.
With 85 to ground not giving any reading means the wire is not grounded or shorted with another ground wire in the harness. The problem is internal to the VCM.
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