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Old May 23rd, 2010, 17:00   #1
scidav87
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Default Freon blowing from checkvalve on compressor?? HELP!

A/C hasn't been working, and the code is 18065 (P1657) "ac sytem input/output short to plus--intermettint" so the A/C never works and my wife is 8 months pregnant and its 90 degrees out. So I went out there today and hooked up a good ground and battery positive to the compressor to see if still worked. All the fuses are good and the wiring lookes clean and untouched. I have no idea what the problem could be. But when I hook up the compressor it turns on, the air gets VERY cold, but then "WISHHHH" freon just blows out on some sort of port or "check valve" on the back of the compressor. So what is that all about?? THANKS
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Old May 23rd, 2010, 17:14   #2
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That's the relief valve. It will open if head pressure exceeds maximum, which is about 20 bar (290 PSI).

Important - do the coolant fans work? An overheated condenser will easily cause a pressure build up in the system. Check the fan control module IAW the service manual.

What was the exact fault code?

Last edited by jcrews; May 23rd, 2010 at 17:16.
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Old May 23rd, 2010, 17:19   #3
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They weren't on at the time, but I had the compressor on manually due to system not turning on automatically. I was seeing if the compressor was still working/good. It was only on for about 5 seconds. I would HATE to have to take the car to the dealer for some silly short somewhere!! Grr Why would it build that much pressure in a matter of SECONDS? Is there some other valve in the system that gets turned on via electrically? I've "hard wired" older a/c systems without a hitch, but not this one it seems. I'm clue less.
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Old May 23rd, 2010, 17:26   #4
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It's an internally regulated compressor so it only relies working on cooling, TXV and the RCV. Everything is mechanical except the pressure transducer, which is used for fan control, load monitoring, and possibly diagnostics.

So, the TXV could have stuck closed enough to cause problems.

In the worst case, the RCV is stuck and compressor displacement is too high. The compressor end cap has to come off to access the RCV.

Last edited by jcrews; May 23rd, 2010 at 17:30.
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Old May 23rd, 2010, 18:02   #5
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Thanks. What does the TXV, and RCV stand for? Anyway to till which one is the problem? Also, when i plug the compressor into the cars pigtail, it doesn't work. And the AC button on the dash is dimmly lite up, whats the cause for that? Got the code back 18065 (P1657) "ac sytem input/output short to plus--intermettint"
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Old May 23rd, 2010, 22:14   #6
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Fuses 5, 25, 16 are assigned to the A/C and FCM.

Check the ground connection, engine compartment, left (under battery tray). The dim light might indicate a bad ground connection.

TXV: Thermostatic eXpansion Valve
RCV: Refrigerant Control Valve
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Old May 23rd, 2010, 22:48   #7
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Battery try was takin out, I have failed as of yet to find the culprit wire. I have heard the control unit (manual) fail on occasion on VW's. Perhaps its in there, I thanks you for the help. I would rather pull the motor and rebuild it than deal with wiring, lol. So much more straight forward.
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Old May 23rd, 2010, 23:09   #8
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More than likely the compressor has failed. If that blow out disc on the compressor is blown time for a new compressor.

There is an aluminum tape applied over the valve, this little "blow out disc" is an indication of impending failure of the compressor.

The compressors are internally regulated to maintain constant pressure by varying the flow of the freon. As a result the fan settings determine the volume they pump by virtue of evaporation rates of the freon to maintain a predetermined evaporator temperature of 35F.

If the compressor is over-pressurizing, the internal regulation mechanism is failed and the compressor will need to be replaced or overhauled (the latter not being an option).
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Old May 24th, 2010, 09:27   #9
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Checked the cooling fans via jumping the thermoswitch pins 1 and 2. Fans dont work and I hear a click and the abs and srs lights go on and the interior "dinger" goes on like i have the lights on, checked power at the driver side fan and pins 1-3 all have 13 volts, not just the 2 pins. The AC button is also lite up all the time. The srs and air bag light reset with a key cycle, until i jump pins 1 and 2 again. The AC light always stays on no matter what. Jumped the fans directly to the battery and the work fine.
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Old May 24th, 2010, 10:00   #10
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Unplug the FCM. Check the A/C to ECM pin. With the switch off, it should have ground potential. On, you should see +12V and the light may turn on. It's unclear because I don't know the ckt resistance at the ECM. It may not allow enough current to flow through the light to illuminate it.

It's FCM pin 8.

Last edited by jcrews; May 24th, 2010 at 10:02.
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Old May 24th, 2010, 10:26   #11
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I have a digital multitester so it will be able to tell the smallest about of power/ground. I checked the fan plugs 1-3 again, and this time it showed 12 volts on low speed, and zero volts at high speed, however, when pluged into the fans still didn't run them at all, so current is more than likely low, even if it HAS 12 volts on occasion. I will unplug the FCM and check pin 8 and go from there. Looks like I may get an FCM off of Ebay and try that if all else fails me. Thanks for the Help!
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