FIXED 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.

 

scannerdanner.com/scannerdanner-premium-...runs-constantly.html
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.

I shouldn't have said all the time. Only when the ignition switch turned to on. And I have a maunual A/C so I should have called it an HVAC control unit instead of Climate controi unit. The radiator fan is also on. Thanks much for the schematics and your input. I don't have it fixed yet but you have advanced my knowldge considerably. In addition, AC freezes up after about 15 or 20 minutes. I was thinking this was a separate problem but now believe that it just needs to cycle in normal operation and its not cycling.

That is the same scenario as the Acura I mentioned.
I think that you will find the AC request is shorted to ground as Ferris all ready suggested.
Maybe disconnect the AC pressure switch and see if there is any change, and check for a short to ground on that circuit while you have it disconnected

You were right. Previous owner had shorted wire going to pin 10 on HVAC control unit to ground in obvious attempt to bypass bad HVAC CU and cause A/C to remain on all time. I rewired it correctly and replaced the HVAC Control Unit and it works great. This also fixed the freezing up problem. Thanks