A/C compressor clutch not engaging

floralvikings

New Member
RonJ said:
With the clutch relay removed and the key in ON(II), do you measure battery voltage at the Blk/Yel wire terminal of the clutch relay receptacle?

The signal that the ECU receives from the control panel is ground for a small reference voltage (5V) on the Blu/Red wire.
Click to expand...

I think I found my problem. The Blk/Yel wire in the clutch relay receptacle was getting voltage, but the blu/red wire at the ECU was not.

I wiggled the probe around and presto! the compressor kicks in, RMPs spike a bit, air starts to cool off. I took a closer look at the wire and it looks like it's a little bit loose in the harness, and wasn't making connection properly until I put the probe in there. So, how should I fix it?
 

RonJ

Banned
floralvikings said:
...the blu/red wire at the ECU was not. I wiggled the probe around and presto! the compressor kicks in, RMPs spike a bit, air starts to cool off. I took a closer look at the wire and it looks like it's a little bit loose in the harness, and wasn't making connection properly until I put the probe in there. So, how should I fix it?
Click to expand...
Congratulations on finally pinpointing the problem. There is a proper way to pin wires into the ECU connector, but I don't have experience doing it. Maybe other members can chime in. Alternatively, you may or may not find useful information at these sites:

http://www.phearable.net/tech/

http://technet.ff-squad.com/
 


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floralvikings

New Member
I don't know if it makes a difference, but when I put the probe in earlier it was grounded to the car. I've been at work since then so I haven't had a chance to test it otherwise.
 

RonJ

Banned
floralvikings said:
I don't know if it makes a difference, but when I put the probe in earlier it was grounded to the car. I've been at work since then so I haven't had a chance to test it otherwise.
Click to expand...
Still suggests a wire or connector terminal problem.
 


floralvikings

New Member
Well, I finally got out to pin the wire I thought was the problem, and I realized that I had been looking at the wrong wire last time. The wire I tested was actually the blk/red wire, at the ECU harness at A15, which I believe you said is the ground to the compressor clutch relay? Anywho, I stuck my probe in there to make sure that I would get the same results I did last time, and I got nothing. Tried checking voltage, nothing.

Then, I tried grounding my probe to the car, like it was last time, and some interesting things happened...

The compressor kicked in good and strong, but my car idled WAY down, actually almost stalled a couple of times, and the compressor stayed on whether the heater control a/c switch was on or not. Blew nice and cold though.

So what does that tell me? To clarify, in pin A15 at the ECU harness, if I insert a grounded probe my compressor comes on regardless of whether the A/C switch is on or not. If the probe is not grounded, nothing happens. I have to go in to work in a few hours but I have all day Saturday to work on it if I can't get it today.

[EDIT]

M'kay. Not measuring voltage at the blu/red wire at the ECU. It's making connection fine, I made sure it was pinned properly. I think I've figured out what's wrong but I want feedback to make sure I'm not mixing something up or misunderstanding how this all works.

If I jump the wire that provides the ground to the compressor clutch relay directly to ground, the compressor kicks on. So, the ECU is failing to provide a ground for the relay? And since the ECU isn't getting voltage from the control panel, that makes sense. So...it looks like I have a bad control panel or A/C switch?

The only reason I would think otherwise is that the condenser fan comes on if I have the A/C switch on.
 

floralvikings

New Member
No feedback? I'd like to get this done today but I looked up how to get the heater control unit out and it looks like a b***h and a half to do :???:

I'd like to be a little more certain that I'm taking the right step before I spend a couple of hours working in the heat :cool:
 

floralvikings

New Member
Well this is... Embarrassing ^.^

So it turns out I wasn't reading voltage anywhere, like period, because my multimeter was on the fritz. I just went out and sprung for a new one and sure enough, voltages here:

At pin A15 at ECU harness, 15v
At pin B5 at ECU harness, 15v with a/c switch off, 5v with a/c switch on
 

floralvikings

New Member
Jumped the pressure switch, still nothing. So frustrating! It's like every time I think I've figured it out I'm either wrong or there's something else >.<

[EDIT]

What I know for sure:

Relays are good
ECU is good
Measuring 15v at ECU pin A15, which provides ground to compressor clutch relay
Measuring the proper voltage at ECU pin B5, which receives voltage from the heater control panel
Jumping pressure switch has no effect
 

floralvikings

New Member
I got in to check the thermostat today, and I saw that there are three wires going into it, one blu/red, one blk/yel, and one yel/wht. The wiring diagram RonJ showed me only has two wires going into the thermostat, a blu/red and a yel/wht. What does that mean for me? I'm assuming the blk/yel is a ground wire, but it's not in the wiring diagram in my manual either...

I also noticed a wire that was definitely not supposed to be there, a black wire electrical taped to the power wire for the fan. I tried tracing it back but it's dark out and I really didn't want to pull out my console to follow it, so I disconnected it and nutted/taped it off. This caused no changes that I could find, but I think it was a wire my old mechanic was using to try and hotwire the compressor to the fan controls. I have tomorrow morning off so I'll go out there and trace it back further when it's light out.
 

hondahappiness

New Member
5+ Year Member
have you by any chance checked the 20 amp fuse in the underhood fuse panel? i had the same problem your having and that was the solution. if i remember correctly its fuse number 8.
 

floralvikings

New Member
Fuse was good, but 25 amps instead of 20. I'm guessing it was replaced incorrectly. I put the proper fuse in, no cigar.

Still tracing back that mystery wire I found, but it looks like it's going behind the heater control panel.
 
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