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False Low Refrifgerant Message - 99 Deville
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bron
New User
Jan 12, 2009, 3:18 PM
Post #1 of 5
(2170 views)
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False Low Refrifgerant Message - 99 Deville
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99 Deville Concours - getting a false refrigerant low message which is shutting down A/C - no trouble codes - mechanic who does general repair has verified that freon/pressure ok, compressor turns, etc. Is one of the temp controls/switches bad or what ??
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 12, 2009, 6:40 PM
Post #2 of 5
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Re: False Low Refrifgerant Message - 99 Deville
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Pretty sure the Caddies use a 'thermistor' for low pressure monitoring. An algorithm of temp and pressure will shut down compressor and or set the low refrigerant light.
Taking a pressure when cool or cold out is futile for the most part. It's a funky calculation of a given pressure at a given temp - algorithm.
Do you have what pressure was noted at what temp? What was the pressure when the compressor was engaged? Temp notation should be the temp about a foot in front of grille BTW,
T
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bron
New User
Jan 13, 2009, 3:02 AM
Post #3 of 5
(2163 views)
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Re: False Low Refrifgerant Message - 99 Deville
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Thanks for response - Don't have temp/pressure data re your response - any way to trick the system ? - there is outside temp measure, inside temp measure
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Jan 13, 2009, 5:58 AM
Post #4 of 5
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Re: False Low Refrifgerant Message - 99 Deville
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Ok: I'm not doubting your mechanic's check of the system but there is a high chance it's just what it says - low on charge.
Unless routine temps are above 70F it's almost pointless to do anything much right now as far as finding or fixing a likely leak.
You do want to fix this for the cooling season? While light is on the compressor should NOT engage as running it low on charge can prohibit the oil in the refrigerant from lubricating it. A/C will come on for short times even in off season when defog/defrost is requested in many vehicles or some just for an 'exercise' cycle to keep oil flowing. IT ISN'T MEANT TO WORK WHEN COLD AS THE GAS COULD CHOKE COMPRESSOR (return as a liquid) SO IT SHOULD SHUT DOWN - KNOW THAT.
To re-set to enable compressor you disconnect neg battery cable for a minute. It will lose all pre-sets and memory for a grace period. My guess is if the plug to compressor's coil (at the clutch head) was safely unhooked and tied away from heat and moving parts it would not come back with the light but might make another A/C related light - perhaps "service a/c soon" or something.
The better thing is if all is quiet now with the system is to just tolerate the light till warmer weather - don't fool with it or add anything till relyable pressures can be taken and leaks found and determined to be slow enough to ignore or in need of repair.
Note: This "Thermistor" system is smart enough to know what pressure the low side return hose should be at a given temp. Not the temp on something you see in the car but on the firewall heater box area. When they don't add up it will disable the compressor as it should. When they don't add up when the temp is allowable and the pressure isn't it will set a light to entertain you!
Sub note: Refrigerant gas is condensable - meaning under pressure at a given temp it becomes a liquid for expansion (evaporation) later.
Sub note ii: This gas and similar gasses is highly temp sensitive. By that I mean the pressure of it contained is wildly effected by temperature. Plain air in a tire for example is sensitive too. Every 10 degrees F. air pressure when contained will drop or rise about ONE PSI vs refrigerant will drop or rise about 10 psi but not on an even curve so you really want to take observations at dang close to 80F for perfect info.
ANALOGY TO THIS: A can of spray paint left in a cold shed in Winter. You try to use it and it won't spray for diddle while cold but will at room temps. It too is propelled by a condensable gas. Pressure is too low when cold to spray paint and the opposite happens when too hot - note cans will say not to expose to heat above "x" F or it may explode and they really could! That same gas is pressured up to sureal pressures at higher temps - same as A/C in some ways.
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In short - strong chance your car is correct but just low on charge and this if cool/cold where you are is not a good time to deal with it. A shop that can keep the car in a temp controlled environment overnight and check/fix things AND fill system by total known weight can do this when cold outside - otherwise wait,
T
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bron
New User
Jan 13, 2009, 6:36 AM
Post #5 of 5
(2152 views)
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Re: False Low Refrifgerant Message - 99 Deville
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Thank you for the excellent rundown - with temps in the 20s to 40s I'll wait till spring - it won't come on so should be no issue till then - again thanks and will let you know hopw turns out
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