BAC Forum
General Boards => Technical Support => Topic started by: Gary Nash on June 18, 2014, 07:25:02 PM
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I have a 97 Marquis with Chassic AC issue. The clutch on the compressor will not energize. If I go the electrical panel & connect the clutch wire to voltage it works. I am unable to find the source of where the voltage comes from that goes to the terminal strip. Question...Does the voltage come from the AC controls or is it routed thru a relay. If it is a relay, where is the relay. A great help would be if I have the schematics for the chaotic AC. Any help to get me in the right direction would be appreciated.
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Gary,
I'm pretty sure it goes through a relay as that would be a lot of current to route through the dash switch. Not sure where it is located but I'd check under the dash and near the AC unit.
Steve
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Gary,
Are you sure that you dash A/C system is adequately charged with refrigerant? There is a pressure switch in the high pressure circuit of the system that interrupts the power to the clutch if there is not adequate pressure. A low state of charge is by far the most common reason for failure of the clutch to engage.
Gerald
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If I am correct, I tried to by pass the high-low switches with a jumper with no change. I think the switches work on ground to ground a relay. (just my thoughts). Still can't find the relay that should supply the for the clutch.
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Gary,
It would be worth checking the static pressure at temperature to see where the system is, given low R134A refrigerant level is the most likely cause for a compressor not cutting in. At 80 degrees it should be about 76PSI low and high side equalized. If it is lower than that then the R134A refrigerant is low. The cut off pressure sensor is probably set to around 20lbs of pressure. Keep in mind with a static pressure of 45lbs the pressure would drop if the compressor came on and the vacuum being pulled would allow the pressure to drop to under 20lbs and you would have an intermittent clutch operation responding to pressure from the compressor operation. Somewhere above 45lbs of static pressure things become stable for accurate charging. This is a table of pressure vs temperature for R134A so you can sort out where you are.
http://www.csgnetwork.com/r134apresstempconv.html
Later Ed