Ecu faulty? (a/c)
#12
06-26-2008 | 08:43 AM
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Joined: Jun 2007
Posts: 10,023
RE: Ecu faulty? (a/c)
Try a different relay first. There's an off chance the relay is bad and overloading things.
If it's not the relay it's the ECU. You can bypass the ECU like you describe and it will be safe to operate. It would work a little better with the ECU in the loop but that would require buying another ECU. For example it's going to stumble as the compressor comes on at idle because the ECU won't be delaying until the engine revs up.
If it's not the relay it's the ECU. You can bypass the ECU like you describe and it will be safe to operate. It would work a little better with the ECU in the loop but that would require buying another ECU. For example it's going to stumble as the compressor comes on at idle because the ECU won't be delaying until the engine revs up.
#16
06-26-2008 | 11:19 AM
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Joined: Jun 2007
Posts: 10,023
RE: Ecu faulty? (a/c)
A15 is the output to the compressor relay, should read less than 1 volt or so with A/C on and battery voltage with it off but key on. This is the other end of the red/blk wire to the relay.
B5 is the input, similar readings. Since the engine idles up with the A/C on, that shows the ECU is receiving the signal on B5 and responding properly.
B5 is the input, similar readings. Since the engine idles up with the A/C on, that shows the ECU is receiving the signal on B5 and responding properly.
#17
06-30-2008 | 10:19 AM
Joined: Jun 2008
Posts: 2
RE: Ecu faulty? (a/c)
I/ve been following this post and the '93 civic I am working on has the exact same problem. My freind brought it to me to replace the compressor so I put a rebuilt compressor, new accumulator and new expansion valve. Pulled a vacuum jumpped the low pressure switch and tried to charge the system. The compressor did not engage. After seeing this post I tried everything here and have come up with the exact voltages on A15 4.2v and B5 .9v with the a/c on. I have read about the a/c switches activating everything correctly but the compressor. Could this be the problem or is the .9v at B5 an acceptable readingand the ECU is the culprit?
Thanks for your help!
Thanks for your help!
#18
06-30-2008 | 10:30 AM
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Joined: Sep 2007
Posts: 9,453
From: Houston, Texas
RE: Ecu faulty? (a/c)
ORIGINAL: fixerman
I/ve been following this post and the '93 civic I am working on has the exact same problem. My freind brought it to me to replace the compressor so I put a rebuilt compressor, new accumulator and new expansion valve. Pulled a vacuum jumpped the low pressure switch and tried to charge the system. The compressor did not engage. After seeing this post I tried everything here and have come up with the exact voltages on A15 4.2v and B5 .9v with the a/c on. I have read about the a/c switches activating everything correctly but the compressor. Could this be the problem or is the .9v at B5 an acceptable reading and the ECU is the culprit?
Thanks for your help!
I/ve been following this post and the '93 civic I am working on has the exact same problem. My freind brought it to me to replace the compressor so I put a rebuilt compressor, new accumulator and new expansion valve. Pulled a vacuum jumpped the low pressure switch and tried to charge the system. The compressor did not engage. After seeing this post I tried everything here and have come up with the exact voltages on A15 4.2v and B5 .9v with the a/c on. I have read about the a/c switches activating everything correctly but the compressor. Could this be the problem or is the .9v at B5 an acceptable reading and the ECU is the culprit?
Thanks for your help!
Have you checked the clutch relay?
Is there power at the red wire leading to the compressor clutch?
Does the condenser fan run?
#19
06-30-2008 | 11:02 AM
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Joined: Jun 2007
Posts: 10,023
RE: Ecu faulty? (a/c)
If the engine idles up that means the ECU intends to turn the compressor on. Condenser fan should be on at that point. Then it's either the compressor relay, compressor, or ECU.
It's not necessary to jump the switch to charge the system. You will be able to get enough pressure in to close the switch without the compressor running.
It's not necessary to jump the switch to charge the system. You will be able to get enough pressure in to close the switch without the compressor running.
#20
06-30-2008 | 05:02 PM
Joined: Jun 2008
Posts: 2
RE: Ecu faulty? (a/c)
System is charged. Relays are good. Fan runs. Clutch engages when relay is jumped. Engine idle increases when a/c is turned on. Again everything is the same as the symptoms above. You mentioned the voltage issues at A15 and B5. I guess my main question is if B5 is .9v should A15 be lower than the 4.2v I am seeing?