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Discussion Starter · #1 ·
Hello,

I finally had the A/C charged on my swap car and am now trying to get the A/C clutch to engage.

This car has the C68 electronic HVAC controller. When the HVAC controller is in Auto, Recirculate, the front and lower vent option, and defrost the Gray/Red "A/C Request" wire from terminal C6 on the A/C Programmer to R15 on the L98 ECM has 0 volts. When I select Off, Front vent, and lower vent the A/C Request wire has 5 volts.

I'm assuming the request wire is supposed to supply 12 volts when the A/C is on. Is this correct?

Because I no longer have the L98 I currently have the request wire wired to the high pressure cutoff switch which goes to the pressure cycling switch and finally the A/C Clutch relay.
 

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I'm assuming the request wire is supposed to supply 12 volts when the A/C is on. Is this correct?
Maybe not.
Don't have the FSM handy but recall there are control voltages less than 12V to the BCM (that controls clutch ) in use

Because I no longer have the L98 I currently have the request wire wired to the high pressure cutoff switch which goes to the pressure cycling switch and finally the A/C Clutch relay.
Control changed during the L98 years
On early ,signal went direct to BCM for compressor control with a separate wire from pressure switch to indicate compressor run.
Later ('90)+?) signal went through the ECM then to BCM
 

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Discussion Starter · #3 ·
Thanks for your help so far. :)

Unfortunately I don't have the FSM but I do have the factory electrical supplement.

Here's what I'm looking at.





Right now I'm not understanding why the A/C request voltage drops to zero when I turn on the A/C and is at 5 when the A/C is off. Do you think the FSM would provide more detail on the operation of the electronic climate control over the electrical supplement manual?

I have the L98 ECM installed in the rear compartment. Currently it only has power, ground, and the two tan serial data wires connected to it. Would it be possible to have the A/C request wire and the Gray A/C clutch relay wire (999 on the diagram above) connected to the L98 ECM so the A/C functions as factory?

If anyone has any ideas they would be appreciated!
 

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How does the output at the connector to the AC compressor react. The voltage signal I think you are checking only goes into the ECM, so that could be handled either way voltage on or off. The ECM is actually sending the signals needed to activate the compressor clutch or not, with the pressure switches inline to make sure the pressure isn't too high or low.
 
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