02 Civic no A/C
#1
10-12-2011 | 12:12 PM
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02 Civic no A/C
I have a 2002 Civic that the A/C doesn't turn on. So far this is what i know about the circuit:
Wire A4 (blue) coming out of the heater control panel is 0v off and 5v on (about). That signal follows to wire F9 (blue/white) too the multiplex control unit and has 0v off 5v on (eliminating possible issues with A/C pressure switch and thermal protection switch)
wire E10 (yellow) at the multiplex has constant 6-7 volts, as well as E24 (yellow) at the ECU, when E10 is depinned voltage is the same until connector E at ECU is disconnected (also had an issues finding that specific wire so back probed and resistance checked until wire was found) Also when connector E at multiplex is plugged in and connected E at ECU is unplugged the 6-7 volts is still there. I have isolated that wire to make sure that my problem isn't in that wire it's self.
My theory is i have a bad multiplex control unit and/or a bad ECU that is back feeding the multiplex unit. But i don't understand what the ECU needs from E24 to engaged the ground (B6 Green - fan control, E18 Red - A/C clutch relay) to get the Relays to turn on.
Any input would be appreciated
Wire A4 (blue) coming out of the heater control panel is 0v off and 5v on (about). That signal follows to wire F9 (blue/white) too the multiplex control unit and has 0v off 5v on (eliminating possible issues with A/C pressure switch and thermal protection switch)
wire E10 (yellow) at the multiplex has constant 6-7 volts, as well as E24 (yellow) at the ECU, when E10 is depinned voltage is the same until connector E at ECU is disconnected (also had an issues finding that specific wire so back probed and resistance checked until wire was found) Also when connector E at multiplex is plugged in and connected E at ECU is unplugged the 6-7 volts is still there. I have isolated that wire to make sure that my problem isn't in that wire it's self.
My theory is i have a bad multiplex control unit and/or a bad ECU that is back feeding the multiplex unit. But i don't understand what the ECU needs from E24 to engaged the ground (B6 Green - fan control, E18 Red - A/C clutch relay) to get the Relays to turn on.
Any input would be appreciated
#2
10-12-2011 | 01:01 PM
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Joined: Jun 2007
Posts: 10,023
The system uses a digitally coded (multiplexed) signal on the yellow wire, you can't probe it simply. When the ECU receives the code it will bump up the idle speed slightly in anticipation of the compressor load, and then engage the relays. Bad MCUs are fairly common. Usually other stuff won't work either such as the dome light and the keyless remote.
#3
10-12-2011 | 02:02 PM
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No there systems in the vehicle are effective, was able to get my hands on a known good multiplex, didn't fix.
How about ECU failures? I didn't think they were as common on Honda's as they are on Toyota's products (I've spent alot of time working on their electrical systems)
How about ECU failures? I didn't think they were as common on Honda's as they are on Toyota's products (I've spent alot of time working on their electrical systems)
#4
10-12-2011 | 02:04 PM
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Can someone give me the voltage that is supposed to coming out of the heater control panel at least? The blue A4 wire? does 5v sound right when on or is it supposed to be source voltage?
Last edited by SwitchAvenger; 10-21-2011 at 07:30 AM.
#7
10-21-2011 | 04:07 PM
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My car has a 4v increase with the a/c turned on. With everything connected and when off it's 5v and when switched on it's 9v. This car has been giving me headache for weeks now. So from your post your saying it could have a pressure switch problem?
