XM Aircon problem

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Jimmydeath
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XM Aircon problem

Post by Jimmydeath » 09 Apr 2002, 05:40

Hello
The aircon on my XM has ceased working, having worked through the electrics I can see that the signal to activate the solenoid on the compressor clutch is not getting through the pressure switch on the receiver dryer.
This could mean one of three things:
1. The pressure switch is knackered (there is no continuity between any of the pins)
2. The Freon pressure is above 26 bar (very unlikely)
3. The Freon pressure is below 1.5 bar (ooh bugger where has my gas gone)
How can I verify that I have any gas in the system at all with loosening a connector and then having it escape? (not environmentally friendly)
Should the pressure switch, in an at rest state, have any continuity at all and if the switch is broken can you change it without letting the Freon escape.
A thought, If I temporarily enabled the compressor clutch by applying 12 volts at its terminal would I be able to see if there is any gas left by looking in the view window of the receiver dryer?
thanks
James
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alan s
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Post by alan s » 09 Apr 2002, 10:25

James,
As a refrigeration mechanic by trade I would strongly suggest you simply take it to an air/con repairer. The reason I say this is that if you start messing around without gauges and say bridge out the pressure switch which will probaly cause the clutch solenoid to activate & we'll say you are out of gas, then the compressor can do a couple of nasty things; draw down into vacuum at which point it possibly will slug all the oil into the refrigeration system & create a big job for someone trying to get it out, and/or suck in a big gutful of air & moisture & contaminate the system giving you problems for years to come. If by the same token it has a blockage or some other problem that has caused it to drop out due to high pressure, then chances are you will either blow the compressor up, blow a line or coil or cause some irrepairable damage.
I feel regardless, you are going to be up for a gas charge & I would almost bet it will be due to short of gas, the reason being that you have just come through winter & hence have not been running the compressor which usually leads to leaking compressor seals.
I trust of course that you haven't been caught as others have in the past & tried to run the air con when the temperature of the day was too cold to trigger the thermostat? <img src=icon_smile_blush.gif border=0 align=middle>
Alan S
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Jimmydeath
Posts: 25
Joined: 14 Feb 2001, 23:05
Location: United Kingdom
My Cars:

Post by Jimmydeath » 09 Apr 2002, 18:04

Thaks for your comments, I didn't know that you could cause serious damage to the system by running it without gas but this is why I asked first.
It is always possible that it was too cold to trigger the system but I was working my way back from the compressor solenoid and found that the solenoid works (engine was not running btw :) ) and the relay that disables the aircon when the engine management system says so also works. The next stage back was the pressure switch, now by connecting a multimeter across the pins of the pressure switch I cannot see any continuity and I would expect to see a short circuit in order for the compressor clutch to operate.
It has been my experience of this vehicle that most of the problems are due to electrical faults which is why I am persuing that avenue.
Is there no way of telling whether the system has any freon in it before taking it to an engineer?
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alan s
RIP 2010
Posts: 2542
Joined: 26 Jan 2001, 16:53
Location: Australia
My Cars:
x 4

Post by alan s » 10 Apr 2002, 03:48

"Is there no way of telling whether the system has any freon in it before taking it to an engineer?"
James,
Without connecting a compound gauge to the suction side, not really. One option is to crack a nut on the suction (low pressure) side of the system which again is really only a rough guide as it would even give a squirt of pressure if the gas level was so low as to not trigger switches or cool. It's not "environmentally responsible" as some fanatical tree hugger would say but by the same token, another spoonful of gas in the mega tons already running around isn't going to start any global disasters <img src=icon_smile_wink.gif border=0 align=middle>
You are right about principle of the pressure switch; it is a basic "make & break" operated by pressure from the system.
Still bot my money on a leak on the low pressure side either at the compressor seal or at the TX valve.
I like the od bet; let me know what it is will you?
Alan S
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