2008 HONDA CRV AC

2008 Honda CRV AC Compressor clutch engaged all of the time.  It will disengage if I remove 7.5 amp fuse under hood.  Also, the AC Condenser fan runs all of the time. It's not a stuck relay.  It's obvious that the PCM is always providing a ground for the control legs of the AC Condenser fan relay and the AC Compressor clutch relay.  I have examined the schematics found on line but I'm not sure how the Climate control panel communicates with the PCM to tell it to provide a ground for these relays.  I suspect through the CAN-H and CAN-L lines coming out of the PCM but I don't see the connection.  P.S.  I've never communicated on a forum so I'm unsure if this is being sent properly. Thanks, Tim Nobles

when u write " all of the time" do you mean the compressor clutch and condenser fan is on with the key out of the vehicle?

i don't know if you have manual or auto a/c so here's both attached at the bottom of this post

I'm not sure how the Climate control panel communicates with the PCM to tell it to provide a ground for these relays.

Researching this topic I learned the Automatic A/C diagram calls their module the Climate Control Unit whereas on the Manual A/C diagram it's called the HVAC Control Unit. Forgive my ignorance on this subject, I'm sure now you're referring to the Automatic A/C system diagram.

I found this helpful techtip in identifix:

The A/C request circuit is a reference voltage (typically 12 volts measured with a voltmeter - not a test light) from the Multiplex Integrated Control Unit (MICU) in the driver's under-dash fuse/relay box that needs to go to ground through the thermal protector at the A/C compressor and then to the heater control panel to ground. When the A/C request circuit is grounded, the MICU communicates to the ECM to tell the ECM the A/C is on, so the ECM grounds the A/C compressor clutch relay to turn on the A/C compressor clutch. The ECM also turns the engine cooling fans on when the A/C request is on.

This MICU inside that fuse/relay box is like a TIPM found in Chryslers. The MICU forwards this a/c request (basically sees 12v pulled low) via B-CAN to the Instrument Cluster, called the Gauge Control Module, which is a gateway module for B-CAN and F-CAN communication, and then the Gauge Control Module tells the PCM on the F-CAN to turn on those relays. I think F-CAN is the CAN high and low you'll find at pins 6 and 14 at the DLC.

Check scan data for the A/C switch and A/C clutch PID. If it says ON, then the CCU is grounding it or there's a short to ground on this wire. Try disconnecting the module and check that wire. One thing I can't explain is why the radiator fan isn't running as well. I thought when a/c is requested, both the radiator and condenser fan should turn on.

 

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I had an 06 Acura not too long ago that wouldn't quit running the AC compressor because the AC request circuit was shorted to ground by a self tapping screw .
The case study is on Scanner Danner Premium if you're interested.