I'm trying to figure out why the AC compressor on a 91 Civic isn't
engaging. There's plenty of freon and the compressor kicks on if I
apply 12V directly. I've followed a diagnostic chart from an Alldata
disc, and it appears the ECU isn't activating the relay. I'm dubious
however that the ECU is the problem.

I don't have the shop manual or wiring diagram, and the Alldata disc
makes no mention of the AC switch on the dashboard. How do I test if
the dash switch is telling the ECU to turn on the compressor? The blue
light turns on when the switch is depressed. I know the kids were
messing around in that area recently to install an aux wire onto the
back of the aftermarket stereo.

Can anyone describe how that part of the system works, and perhaps a
pin on the ECU to check for 12V or ground with dash switch on/off??

-RC

 

"RC" <spam_this@nowhere.null> wrote in message
news:1t80m59chh5jkvpp7g0lrlme89hbkn5q4i@4ax.com...
> I'm trying to figure out why the AC compressor on a 91 Civic isn't
> engaging. There's plenty of freon and the compressor kicks on if I
> apply 12V directly. I've followed a diagnostic chart from an Alldata
> disc, and it appears the ECU isn't activating the relay. I'm dubious
> however that the ECU is the problem.
>
> I don't have the shop manual or wiring diagram, and the Alldata disc
> makes no mention of the AC switch on the dashboard. How do I test if
> the dash switch is telling the ECU to turn on the compressor? The blue
> light turns on when the switch is depressed. I know the kids were
> messing around in that area recently to install an aux wire onto the
> back of the aftermarket stereo.
>
> Can anyone describe how that part of the system works, and perhaps a
> pin on the ECU to check for 12V or ground with dash switch on/off??
>
> -RC

There should be a pressure switch close to your receiver/dryer that signals
the ecu to power the compressor. If you don't have enough gas in the system,
the ecu will not engage the compressor.

You have a leak in the system. Have it tested.

 

On 1/27/10 5:36 AM, in article 1t80m59chh5jkvpp7g0lrlme89hbkn5q4i@4ax.com,
"RC" <spam_this@nowhere.null> wrote:

> I'm trying to figure out why the AC compressor on a 91 Civic isn't
> engaging. There's plenty of freon and the compressor kicks on if I
> apply 12V directly. I've followed a diagnostic chart from an Alldata
> disc, and it appears the ECU isn't activating the relay. I'm dubious
> however that the ECU is the problem.
>
> I don't have the shop manual or wiring diagram, and the Alldata disc
> makes no mention of the AC switch on the dashboard. How do I test if
> the dash switch is telling the ECU to turn on the compressor? The blue
> light turns on when the switch is depressed. I know the kids were
> messing around in that area recently to install an aux wire onto the
> back of the aftermarket stereo.
>
> Can anyone describe how that part of the system works, and perhaps a
> pin on the ECU to check for 12V or ground with dash switch on/off??
>
> -RC

If, as you say "the kids were messing around in that area recently to
install an aux wire...", the first thing to do is check ALL the fuses under
the dash and under the hood to see which one they blew. Then pull the radio
and trace all the wires that were messed with and see where they tapped into
the wrong one. You will need a wiring diagram for this. You should be able
to find the service manual/wiring diagrams on line somewhere. Start with
www.tegger.com/hondafaq/

 

If you have Alldata, all the necessary wiring diagrams are there, along with
ground locations and trouble trees. It's also helpful if you have some
experience in this kind of troubleshooting.

 

On Wed, 27 Jan 2010 13:01:08 -0500, "Ed" <electro@hvc.rr.com> wrote:

>
>
>If you have Alldata, all the necessary wiring diagrams are there, along with
>ground locations and trouble trees. It's also helpful if you have some
>experience in this kind of troubleshooting.

First, a response to earlier messages-

1) I repeat, there's plenty of freon. I hooked up my gauges and
pressures are normal. That's the first thing I did. Compressor was
replaced by me about 1 year ago with a unit from Arizona Air, along
with receiver and expansion valve. Recharged with R12.

2) I checked the fuses. They're fine. The relay is getting 12V on both
the hot wires. That's part of the Alldata troubleshooting. It isn't
seeing ground from the ECU.

Back to the Alldata discs. I bought these back when the car was nearly
brand new (early 90s). I've dug around and can not find comprehensive
wiring diagrams on the disc.

I'll check again.

-RC

 

Followup. I found the wiring diagrams on the Alldata discs. I have
plenty of experience with this kind of thing. I'll try to report back
what the problem is. :-)

-RC


On Wed, 27 Jan 2010 13:01:08 -0500, "Ed" <electro@hvc.rr.com> wrote:

>
>
>If you have Alldata, all the necessary wiring diagrams are there, along with
>ground locations and trouble trees. It's also helpful if you have some
>experience in this kind of troubleshooting.