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Hi all,

I own an opel astra h 1.7cdti, 100hp, 2004 with the engine code z17dth.
This model has an automatic a/c compressor (clutchless).

My problem is the A/C is not working. Compressor does not kick in. ECM produces p0530. System is fully gassed, no leak or anything. A/C pressure sensor replaced, still nothing.

If you manually apply 12 (or 14V) to the compressor electrical input pin, you can hear the "click". This made me think the compressor is ok. I measured the resistance in between the two pins of the electrical connection of the comrpessor, which gave around 11 ohms. Could this be the problem?

During manual 12V application to the compressor, although you hear the click, it still does not blow cold. Is this because the compressor must be controlled by a PWM signal, instead of a fixed 12V DC all the time?

What else I have done to diagnose the issue is the following:
-When the AC is on from the dash, one of the pins of the compressor is getting 12(14V). The other pin however apparently is not the GROUND. There is no continuity to the sytem ground from there. Is this because the ECM should make it Ground provided there is no error? Some kind of switched ground topology maybe? If you try to measure the DC voltage in between these two pins, you see sth like 1.76V. Maybe an oscilloscope is needed here (I dont have one
), maybe there is a PWM signal reaching there...
-I have disconnected the 3 wire electrical cable of the AC pressure sensor. One of them is ground, and the other one is 5V reference. The output signal, the third one was 0V of course since it was not connected to the sensor... I could not measure that while it was connected to the sensor, maybe I somehow need to strip the cable and do so.

So far does these make any sense to you at all?

P.s. one place took a look and claimed to have checked everything, and suggested a ECM replacement. Found a 2nd hand, got it reprogrammed, AC is still not working and p0530 keeps re-appearing if you clear it out. Also, if you try to read the A/C pressure from opcom or tech2, it says 0, when the system is supposed to be full of gas. This is somehow making me think there is a short or open somewhere I do not know... I do not have experience at all about cars in general, just tried my best with my multimeter. I do not even have any diagram of circuits or anything...

Your help is much appreciated.
 

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Hi there, i dont know the answer but i would think if you energize the clutch manually and it still doesn't work then the compressor is faulty....all you can really do at this stage is take it to an air con place and get the pressures checked, i guess there could be blockage somewhere....think the fan is supposed to run at the radiator end, i assume all the controls are working ok, can you feel the pipes see if they get cold....from Fred in Essex.
 

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Discussion Starter #3
Hi there, i dont know the answer but i would think if you energize the clutch manually and it still doesn't work then the compressor is faulty....all you can really do at this stage is take it to an air con place and get the pressures checked, i guess there could be blockage somewhere....think the fan is supposed to run at the radiator end, i assume all the controls are working ok, can you feel the pipes see if they get cold....from Fred in Essex.
Hello sir. Thank you for your message. When externally energized with a DC voltage, you hear the click, is it not enough to say that it is ok? What I am not sure is, maybe it does require a PWM signal, which tells the thing to work based on a duty cycle information rather than DC voltage...
The pipes do not feel cold. One place checked the system and regassed it, although there was gas in it, not full, but enough. Another observation I made myself is that the condenser looks really bad, the very bottom plate was loose from one end for example. Do you think it may have anything to do with this?
 

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Well i wouldn't thik that would have anything to do with it, as long as the pressure remains in the system...you may be right about the compressor...if its not engaging properly it wont turn the pump...without having the pressure checked with it running its impossible to be sure...Fred.
 

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What you could try it let the car idle and then energize the clutch and see if the engine slows down...i know you have an automatic idle device but you should still be able to detect a difference, if t stays the same the pump prob isn't working....Fred.
 

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What you could try it let the car idle and then energize the clutch and see if the engine slows down...i know you have an automatic idle device but you should still be able to detect a difference, if t stays the same the pump prob isn't working....Fred.
Well I guess that is a two man job, even if there s a momentary load on the engine, which I doubt I can recognize, as there was no such observation of mine during the days when the A/C was working fine... I will maybe try that at some point. I just wish that I had a car with a manual compressor, maybe things would not be this hard to figure out. I on the other do not want to convert this to a manual one either, which apparently is a tendency to do among many mechanics...
 

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I have done further measurements. When the car is on, and everything is connected. I measured the voltages on the 3 wire of the a/c pressure sensor/switch.
One of the wires were 5.2V or sth. I guess this is the reference voltage coming from the ECU.
The other one was around 0V, which is the Ground.
The third wire, which I am guessing the signal of the air pressure sensor, was around 0.11 V.

This seems to be very low to me. Does it mean that the a/c pressure sensor is broken? I had recently ordered this, and I am having difficulty believing that this is the case... Could it mean that this signal is not reaching to the ECU? So the ECU thinks there is something wrong and disabling the compressor? (I mean if there is a brake at the cable, maybe that is why we see 0.11V, not that the A/C switch is broken, just the circuit is not complete due to a break in the cable)...
 

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Hi there well it all makes sense what you say, without a wiring diagram i dont know how its wired up, but sensors generally work like that, a 5v reference from the ecu and a ground and a signal wire, it might be worth disconnecting the the sensor and getting a test light put one end to battery positive and the other end to the ground wire to make sure the ground it really good....vauxhall grounds are normally brown...but i would thing all three wires go to the ecu...so it might be brown with a trace on it....how many wires are on the compressor clutch?....i would think that would have a 12 volt or duty cycle and a ground...from Fred.
 

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Hi there well it all makes sense what you say, without a wiring diagram i dont know how its wired up, but sensors generally work like that, a 5v reference from the ecu and a ground and a signal wire, it might be worth disconnecting the the sensor and getting a test light put one end to battery positive and the other end to the ground wire to make sure the ground it really good....vauxhall grounds are normally brown...but i would thing all three wires go to the ecu...so it might be brown with a trace on it....how many wires are on the compressor clutch?....i would think that would have a 12 volt or duty cycle and a ground...from Fred.
I dont have a diagram myself unfortunately. If my memory does not betray me, I think you are right. The brown was the ground. I did a continuity test from that to the battery negative, it was seemingly ok.
The compressor's electrical connection has two wires. One gets 12V if the A/C is on from the dash, the other is I am just guessing here, is a switched Ground. IF everything was ok with the system, ECU would make this ground. But since it is not, its like a floating node. Like I expressed in my first message, the voltage difference between this and 12V is like 1.76V when the A/C is on. OR maybe there is a PWM signal which I cannot read via a DC multimeter. I will not know more until I find an oscilloscope I guess. I wish I had a system diagram at this point...
 

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Yes sure there are others on here that know more than me about it, but i would have thought if you put 12 volts across the two wires on the clutch it ought to engage and with the engine running the A/c should work, that kind of eliminate all the ecu stuff...think you said the pipes were cold, if that is so it ought to be working....Fred.
 

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Discussion Starter #11 (Edited)
Yes sure there are others on here that know more than me about it, but i would have thought if you put 12 volts across the two wires on the clutch it ought to engage and with the engine running the A/c should work, that kind of eliminate all the ecu stuff...think you said the pipes were cold, if that is so it ought to be working....Fred.
Thanks again, sir. If it was a manual, clutch type compressor, yes it should run the AC system just like that. According to the research I did, automatic pumps or voltage displacement type or in other words clutchless ones require an ever changing PWM signal. This makes the internal plate change angle and make the thing compress. So, a direct 12V cannot make it work sir. No, I said the pipes are not cold. But I do not know whether it is relevant, but the compressor body itself gets very hot. Regardless if the A/C is on from the dash,or off, it is really hot.
 

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I must also add, I think the signal of the a/c pressure sensor also is a PWM signal between 0 and 5 V. So measuring its DC voltage also was not a good idea. I will know more when I have an oscilloscope.
 
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