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Under Pressure 

 

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 Post subject: Under Pressure
Posted: Wed Sep 14, 2016 9:53 am 
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Hi all, just wondering who knows what the air-con gas pressure is. I have been gifted a clean ED XR6 and the owner said he had the evaporator replaced and system worked great for a few months then stopped working. As he knew he was going to give the car away he never went back to the tech who done the evaporator. I know how to bypass the low gas pressure switch and the compressor works with no noises and runs smooth. What i would like to know is what the gas pressure is while the system is not operating. I'm pretty sure some one on our wonderful FORDMODS :mrgreen: site can fill me in,
cheers shaddoweaver :D

 

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 Post subject: Re: Under Pressure
Posted: Wed Sep 14, 2016 2:20 pm 
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What's the point in knowing that ?

 

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 Post subject: Re: Under Pressure
Posted: Wed Sep 14, 2016 8:59 pm 
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:?: takes low pressure switch fault out of the equation :?: Seems like a perfectly good question to ask. I am a disabled pensioner (not elderly or senile ) trying to save a dollar. I do have some 30 years working in engineering and know my way around petrol engines although I never worked with Air Conditioning. I am open to any suggestions and criticism.

 

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 Post subject: Re: Under Pressure
Posted: Wed Sep 14, 2016 11:55 pm 
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Well all you can do with the above operation is do a touch test on the pipeline around the low side port, should be getting cold. Don't run the compressor too long like this - if it's low gas it won't be getting any lubricant.
You can get a screwdriver and quickly and lightly press the high side valve (near the airbox)and see if there's actually any gas left in the system.
Post back your findings.

 

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 Post subject: Re: Under Pressure
Posted: Thu Sep 15, 2016 6:19 pm 
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shaddoweaver wrote:
Hi all, just wondering who knows what the air-con gas pressure is. I have been gifted a clean ED XR6 and the owner said he had the evaporator replaced and system worked great for a few months then stopped working. As he knew he was going to give the car away he never went back to the tech who done the evaporator. I know how to bypass the low gas pressure switch and the compressor works with no noises and runs smooth. What i would like to know is what the gas pressure is while the system is not operating. I'm pretty sure some one on our wonderful :mrgreen: site can fill me in,
cheers shaddoweaver :D



"static pressure in the system?

Before the vehicle is started, the static system pressure can be read. Pressure should be very nearly equal in both gauges. Actual pressure will depend on the type refrigerant and the ambient temperature and does not show if the system is properly charged. At 85 degrees Fahrenheit, R134A shows a pressure of around 90 pounds per square inch. Much lower readings suggest the system is low on charge or contaminated with air. At least twenty-five PSI of static pressure is required, or the cycle switch may disable the compressor."


take note of snap0964 post as if you can operate a/c by turning a/c on and bridging low pressure switch low gas is most likely cause and would indicate a leak somewhere or a faulty switch (occassionally)
feel test of low side pipe(larger pipe) should be cold when operating and hi side will be warm to hot - as mentioned running with low gas can damage due to no lubrication
it won't take much gas to give you the static readings which is why you generally fill from empty by weight...........look for any wet patches around pipes-condensor and compressor for possible indication of a leak.................

side note - make sure your condensor is clean and fan is working,however this is normally relevant to a system that works for a while then stops cooling.........
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 Post subject: Re: Under Pressure
Posted: Thu Nov 10, 2016 8:44 pm 
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thanks everyone for responses. due to health issues and several leaky welch plugs it's been a while to investigate air-con system. ok here goes, snap tried shorting low pressure switch & ran system. results were slight hissing at tx valve, no difference in temp on any pipes, & only small amount of gas escaping from from quick press of valve. tedW, i couldn't get any pressure readings from any valves probably due to not having correct equipment. i took the warning from both you and snap not to run the a/c for long, a minute at most. so took the car to a/c specialist. results are they vacuumed the system down and held for 40 minutes all good there. they the gave it a small charge to test system but no go. so with further investigation the tech found some one had removed a relay for the a/c :? . he thinks it may have been used to replace a fuel pump or headlight relay in an emergency. any way he put a new relay in and the system fired up. they gave it a full charge of gas with leak detection dye and runs nice and cold. total cost so far $307. very falcon happy :D . i was told the compressor is a bit lazy and is typical :?: . any way still falcon happy. thank you snap & tedW for your advice and warnings.

 

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