ABS Light...

[mptc]

I checked for power to the clutch harness...nothing. I traced back to the relay and there is power to the relay. I checked the relay again and it is operational. So there must be a short somewhere between the relay and the clutch? I did notice a fusible link between the relay and clutch although the wiring diagram does not indicate it. Is there a way to by-pass the wiring and go straight from the relay to the clutch to test if the clutch engages or not?

mptc

[Tech II]

You have power to the relay, but is the relay being commanded on? When you have someone turn the A/C on with the car running, do you feel/hear the relay click? If the relay is ok, the PCM is not grounding it...

The only way to check this out is with a scan tool.......you have a pressure sensor code...clear it.....does it come back when you command the A/C on?

With a scan tool, you have to look at the data from the pressure sensor.....since gages said you had 90psi, then the sensor should be reading the same pressure....if it is reading too high or too low, the PCM will not command the compressor on.....

Also there is another input to the PCM....that is A/C request.....if the PCM does not receive a request from the HVAC head, it will not command the compressor on....need to see this on the scan tool.....

You can disconnect the PCM and jumper the A/C relay circuit to ground(no key in the ignition, disconnect battery, then disconnect all the harnesses to the PCM.....reconnect battery......turn key to on....now jumper the relay circuit to ground....you will need a wiring diagram to know which line to jumper.....) but all that will do is validate the clutch circuit, if the clutch clicks, my money is on the sensor, and you need a scan tool to validate this.....

[mptc]

Originally Posted by Tech II

You have power to the relay, but is the relay being commanded on? When you have someone turn the A/C on with the car running, do you feel/hear the relay click? If the relay is ok, the PCM is not grounding it... Okay...did not hear or feel a click.

The only way to check this out is with a scan tool.......you have a pressure sensor code...clear it.....does it come back when you command the A/C on?

With a scan tool, you have to look at the data from the pressure sensor.....since gages said you had 90psi, then the sensor should be reading the same pressure....if it is reading too high or too low, the PCM will not command the compressor on.....

Also there is another input to the PCM....that is A/C request.....if the PCM does not receive a request from the HVAC head, it will not command the compressor on....need to see this on the scan tool.....

You can disconnect the PCM and jumper the A/C relay circuit to ground(no key in the ignition, disconnect battery, then disconnect all the harnesses to the PCM.....reconnect battery......turn key to on....now jumper the relay circuit to ground....you will need a wiring diagram to know which line to jumper.....) but all that will do is validate the clutch circuit, if the clutch clicks, my money is on the sensor, and you need a scan tool to validate this.....When jumping the A/C (C2) relay to ground I heard an audible click and felt it as well. I even took the relay off the bracket and held it in my hand to make sure it was the one clicking.

According to Chilton I have high and low pressure cut off switches. According to the wire diagram I have an A/C pressure sensor only. The wiring diagram matches what I am seeing. Is it necessary to verify that it is the pressure sensor or have we narrowed it down by deduction to that. Or am I getting ahead of myself? Is there another possible explanation (other than a short between the relay and compressor). Can it be changed without discharging the system?

Thanks!

mptc

[mptc]

One clarification on the information above...the click I heard and felt was the relay only. I did not hear or feel a click in the clutch itself. I had the A/C control in both normal and max position in addition to the off position.

mptc

[Tech II]

As I said in post #17, if you want to check the ENTIRE relay circuit, you have to diconnect the PCM(with battery disconnected first).....then reconnect battery......with the key on(engine not running), then you need a wiring diagram to know which circuuit in one of the harnesses is the ground control for the Compressor relay......if you ground that circuit, the relay clicks, and the compressor clutch should click as it is pulled in....If that happens, you know the ENTIRE CIRCUIT IS OK.....Then you are dealing with a possible sensor problem, that can only be verified wioth a scan tool....if the relay clicks, but the clutch does not, then you check for power at the harness of the clutch for power and ground with a test light...

In some cases, if an A/C code is set, it may have to be cleared before the A/C system can operate......if you have an A/C code, clear it, then operate the system, it doesn't run, and the code comes back, then the sensor will have to be checked with a scan tool......

[mptc]

Originally Posted by Tech II

As I said in post #17, if you want to check the ENTIRE relay circuit, you have to diconnect the PCM(with battery disconnected first).....then reconnect battery......with the key on(engine not running), then you need a wiring diagram to know which circuuit in one of the harnesses is the ground control for the Compressor relay......if you ground that circuit, the relay clicks, and the compressor clutch should click as it is pulled in....If that happens, you know the ENTIRE CIRCUIT IS OK.....Then you are dealing with a possible sensor problem, that can only be verified wioth a scan tool....if the relay clicks, but the clutch does not, then you check for power at the harness of the clutch for power and ground with a test light... As I mentioned in post #16 I did check power to the harness with a test light. There was nothing. I checked power to the relay and there is power there. And I did check the entire circuit by disconnecting the PCM...post #18. The relay clicked but the clutch did not.

In some cases, if an A/C code is set, it may have to be cleared before the A/C system can operate......if you have an A/C code, clear it, then operate the system, it doesn't run, and the code comes back, then the sensor will have to be checked with a scan tool......

Now here is the interesting part. I wanted to check if the wiring from the relay to the harness plug was good or bad. I started the engine and turned the A/C on and stuck the point of my tester into the power (green) wire just below the relay at different spots. Nothing. So I turned off the engine (disconnected the battery) and about an inch below the relay I stripped the green coating from the power wire that leads to the compressor. I reconnected the battery, started the engine and the A/C and I jumped the power (green) wire to the battery (pos.) and the compressor clutch engaged and ran. I let the engine run for 5 minutes. It did not put out any cold air but the clutch was engaged and running the whole time. So this verifies that the power (green) wiring from just below the relay to the compressor is good.

So in summary....I have 1) power to the relay. 2) The relay itself is functioning. 3) from the PCM harness to the relay is good because it engages (clicks) the relay when jumped to ground. 4) the power (green) wire is good from just below the relay to the compressor because when jumped to the battery the compressor clutch engages.

So why when I did the test from the PCM harness did the relay click but the compressor clutch did not? Could there be a problem not with the relay but with the base that the relay plugs into?

Again thank you for your imput!

mptc

[Tech II]

Do an ohm check between the green wire and the contact in the base that goes to it....if "OL" you found your problem.....if it reads zero, even though the relay clicks, did you try another relay?

You say you checked for power to the relay....was there power on two legs?

[mptc]

Originally Posted by Tech II

Do an ohm check between the green wire and the contact in the base that goes to it....if "OL" you found your problem.....if it reads zero, even though the relay clicks, did you try another relay? I will check this.

You say you checked for power to the relay....was there power on two legs?Yes there was power on two legs.

Thanks!
mptc

[mptc]

Okay I think I discovered the problem(s). First of all...I did an ohm check and it was fine (no problem there). To verify, I removed the relay and jumped from the battery to the contact on the base where the green wire goes and it engaged the compressor clutch. So the relay, the base and the harness are all good. Now for the other problem that I discovered. When jumping from the battery to the contact (green wire) the clutch did not engage at first. I reached down and discovered some play in the harness when it is plugged into the compressor. I moved it to the right and the clutch engaged. I moved it left and it quit. This is not alot of movement but enough to start and stop the clutch. This is probably why the clutch did not click when I jumped the PCM harness wire to ground (post #19). So I agree with you that the pressure sensor is the ultimate culprit. If it is faulty this does keep the power from going to the compressor harness, correct?

Thanks!
mptc

[Tech II]

If the pressure data from the sensor is too high or too low, the PCM will not ground the relay, to power the clutch.....

Unfortunately, the only way to know for sure, is with a scan tool...A/C codes must be cleared and data from the sensor must equal the pressure readings from the gages....AND an A/C request must be present....

As for your clutch contact...it's either the contacts in the harness(are they tight enough?) or a bad contact in the clutch itself.....

[mptc]

If the pressure data from the sensor is too high or low then the sensor is malfunctioning. Have all other possibilities been eliminated? Is so, then is it necessary to determine how it is malfunctioning? Why not just replace the sensor?

Thanks!
mptc

[Tech II]

You could do that....and it still might not work.......What if the sensing line is an open circuit?

But since you don't have access to a scan tool, it might be your best guess....

[mptc]

Originally Posted by Tech II

You could do that....and it still might not work.......What if the sensing line is an open circuit?

But since you don't have access to a scan tool, it might be your best guess....

Is it possible to measure voltage in the sensing line with the key turned on and the A/C turned on to verify power is going to the sensor?

Thanks!
mptc

[mptc]

Same car expanded problem.

First of all I will let you know how the A/C pressure sensor problem works out shortly. The part will be in this week.

Secondly, the ABS problem has morphed or expanded into a new problem. The car is blowing the 10 amp fuse for (electric fan/starter and generator/seq. fuel inj.V-6/cruise control/anti lock brakes) as fast as I put them in. It started slowly and now the fuse blows when I turn the key to on without starting. It has a significant loss of power/performance when this happens.

I tested the brown wire leading out of the fuse all the way to the generator and there is continuity. I found a main ground (one of three grounded to the engine block) that had the coating chewed by rodents. So I cleaned off the exposed wire and wrapped it in several layers of electrical tape as well as the plastic casing. It still blew the fuse.

Help!

mptc