2002CivicTDA

Good Morning,

2002 Civic LX Manual

My a/c clutch will not engage without being hot wired.
All Control panel switch/dials seem to be in working order.
I've even used another recir, ac, and defrost control unit with same results.
One of the techs at my job says I'm not getting signal ground at the relay, from the ECU.

AC Pressure Sensor : I have continuity
Thermal Switch "on compressor : I have continuity
I've checked all Fuses
Radiator/Condenser fans kick on when temp requires

***Condenser fan does not turn on when I press the AC Button***
Any Help is appreciated.

ezone

BOTH of those radiator fans are supposed to turn on.

Anyway......

That seems to indicate the AC request signal isn't reaching the PCM. (Would be nice to be able to see live data from the PCM for confirmation though)

Unplug the 3 wire connector for the compressor and bring the cars harness end up where it's easy to reach.
Start engine, turn on the AC.
Using a grounded jumper wire, CAREFULLY make contact with the terminal for the blue/white wire.

Does that make the fans run and clutch engage?





Does the car have any other unusual electrical gremlins going on? (dome light wonky, door ajar beeper quit, wiper/washer lost a function, etc)?

2002CivicTDA

I jumped the engine side BLUE/WHITE wire, per your request.
AC Clutch did not engage, both fans came on immediately.

ezone

Damn, this may not be simple now.

You just simulated the AC ON request to the ECM. You didn't have that response before, so that's one problem to chase down: Lack of AC REQuest signal somewhere from the control panel to the point you connected the jumper.. Need more testing from that direction.

Next problem:
Relays for both fans and compressor clutch are supposed to all be turned on at the same time.


Since we know you just made the fans turn on (the ECM received the request) you could now pull the clutch relay and use volt-ohm meter to verify if that signal is actually present that comes from the ECM (ecm grounds one side of the relay coil to make it engage)

Actually if you know basics of relay operation you can check all 4 terminals of the relay socket and that leads to the next decision step. I do this in about 5 seconds with a test light LOL

2002CivicTDA

I guess I should have mentioned that from the beginning.
I tested the fuse panel, top and bottom side.

No ground signal at the rely, I had a mechanic at my job verify my test.

I also back probed ECU red wire and fuse black red wire "bottom and top side" for ohms.
All wiring seems to be intact.

ezone

BUT at that time you apparently did not have any AC REQuest to the ECM either, because you said you had no fan action when you turned on the AC. Therefore the ecm would not even attempt to turn on the clutch relay.

NOW that you know how to 'force' the ECM receive the request (by grounding the terminal) keep doing that while you (or your mechanic) recheck to see if the clutch relay is now receiving a correct signal.



Kinda want to make sure the compressor is gonna be able to turn on when the ecm tells it to before digging deep into the request side of the problems.

2002CivicTDA

2002CivicTDA

Sir,
I back probed the engine side blue/white wire w/grounded jumper wire.
****This turned on the 2 fans and the AC clutch engaged.***

I did verify ground from the ecm to the ac clutch relay.

ezone

Sounds like that end will work when it's told to work, so you now need to figure out why the AC request signal gets lost.


You did say your thermal protector is not open circuit, right?



Part of the AC request signal is done by simply grounding the wire that runs from the control panel to the pressure switch and thermal protector......so

In that same 3 wire connector you've been probing, move to the other outside wire and (when control panel is set for AC on) check that that wire is grounded using volt-ohm meter?

Backprobing without disconnecting a connector is even better.



Or you could plug it back in and move to the pressure switch and try grounding terminals there. Basically you're gonna be working thru the system backwards testing and/or supplying the ground at the 3 possible component connectors (thermal protector, pressure switch, and control panel) to confirm the request line is or is not open circuit somewhere between 2 points.

2002CivicTDA

I'm a little confused. So, i'll tell you what I have confirmed.

Thermal Protector : the two outside wires on the compressor pigtail has continuity
Pressure Switch : Has continuity

If I unplug my pressure switch pigtail, where do you want me to supply the grounded jumper?

ezone

Check on both. One should make the AC kick on.

ezone

Assuming the above works, then move to the HVAC control panel. Remove and unplug it. Ground the blue wire in cavity A4 of the 14 connector. AC should turn on.

2002CivicTDA

Ok.
I supplied a grounded jumper wire to the red wire on the Pressure Switch.
Fans and clutch turned on.

Which cavity would be A4?

ezone

Remove and unplug the HVAC control panel. (the control unit is behind the dials not the pushbuttons)
It has 2 large connectors.
One has 14 cavities.
Find the blue wire in that one.

2002CivicTDA

2002CivicTDA

ezone

Check HVAC panel for fault codes (you will have to search for procedure and list of codes)


Assuming there is no code for fan feedback nor evap temp sensor,

You probably have a bad HVAC control panel. (the part with the dials, not the pushbuttons)



A used and unknown panel may be a bad one (they do go bad). Know someone with an identical car you can swap the part for testing?

2002CivicTDA

ezone

I can't look it up either. What's the definition?

Yea. What you did proves the AC will run once the pcm receives the 'ac request' (unless it has some other problems you will discover after it's actually been running again). Your control panel is not grounding the AC request line. Assuming the code 9 is not related to the fan or temp sensor.

2002CivicTDA

Thank you.

I'll trying to pickup a used control unit this weekend and update you on Monday.

ezone

Used might not be a good one either. They do go bad.

2002CivicTDA

2002CivicTDA

2002CivicTDA

Would you happen to have a professional wiring diagram for the AC?

Colin42

Look at the most recent link in this thread:
https://www.civicforums.com/forums/1...e-updated.html

It should have the diagrams you need

ezone

Yes, I have access to that.
No, I cannot provide the same info to you or anyone else.
When I give links, it's because I searched and found the info already posted on the internet by someone else.

See Colins link in his post

2002CivicTDA