Ac Clutch Not Engaging 2000 Buick Century

TomY

New member
9
0
1
Buick Ownership
Century
Hi Guys:
With the warm weather coming I wanted to get my AC running on my 2000 Buick Century. I evacuated the system, held a vacuum for 1 1/2 hours, went to charge the system but the ac clutch would not engage. I checked the fuse and relay which checked out ok so I jumped the ac relay which engaged the clutch and put 1 can into the system reinstalled the relay but the ac clutch still would not engage. Jumping out the relay again I added a second can of Freon reinstalled the relay but still no ac clutch engagement. Seems to me 2 cans should be enough to let ac clutch to cycle on? I'm new to this Buick and are asking for any input to help me resolve this problem. Does this system have high and low pressure switch's? I read that there's a sensor that tells the ECM to signal the clutch to turn on, were might this sensor be located. Do I need to check with my scanner the HVAC menu for problems associated with malfunction. Any help is greatly appreciated. Thanks.

Tom Y
 

chem_man

Buick Newbie
291
98
28
Fallston, MD
Buick Ownership
1999 Century
Try jumping the low pressure switch that is installed on the accumulator. Unplug the connector and stick a paperclip or a jumper wire into the connector. If that does not work then you'll need to see if the compressor is getting voltage. If it is, then check the air gap on the clutch. As the compressor ages, it seems like the air gap needs to decrease a tiny bit.
 

ulycyc

Well-known member
542
272
63
Long Island, New York
Buick Ownership
1987 Turbo Buick, 2001 Park Ave Ultra
No sensor on the accumulator. That's on older cars. The pressure sensor is on the liquid line under the air cleaner assembly. You also may not have enough pressure equalized in the system. Try another can first and make sure your getting some pressure readings on your gauge set.
 

TomY

New member
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1
Buick Ownership
Century
Thank for your reply, chem_man & ulycyc. The clutch engages with no problem when i jump the relay out. I put 2 cans in which is 1.5lbs. and system calls for 1.88lbs. I would think this would be sufficient to at least cycle the clutch on/off. As for jumping the pressure switch it is a three wire unit and I'm not sure how to jump it out. From what I read one of those wires signals the PCM which tells the clutch to engage by completing a ground to the AC Relay. I would be afraid to jump out the wrong wires and fry the PCM. What I need is an OEM Factory Service Manual with wiring diagrams so I can check out the printouts of all wires. Thanks again.

Tom Y
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ulycyc

Well-known member
542
272
63
Long Island, New York
Buick Ownership
1987 Turbo Buick, 2001 Park Ave Ultra
As I asked before, What is the low pressure reading on your gauge set. If its below 35psi the clutch wont engage. Yes your put Freon in but it may not reach the liquid line due to blockage, orifice tube bad or whatever. You can also use a tech2 style scanner to test the ac circuit, sensors and controller.
 

TomY

New member
9
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1
Buick Ownership
Century
Ya when I put the 2 cans in low pressure was about 30psi with the relay jumped out. Will try adding a little more. Hate using cans, waiting for my 30LB can and prefer charging by weight Thanks.
 

TomY

New member
9
0
1
Buick Ownership
Century
Hey ulycyc, added just about another can and pressure went from 30 to 35psi on the low side 300 on the high side put relay back in and no difference. Was trying to get into HVAC module with my Autel MX 808 which I thought I had done before but couldn't. I could be mistaken and it was another vehicle but why the scanner was connected I found a P 1546 code ( A/C Clutch Status Circuit Low Input) which I need to address. Any Ideas on what that could be. Any direction to look at would greatly appreciated. Thanks.

Tom
 

TomY

New member
9
0
1
Buick Ownership
Century
Hi any know what ac request input voltage should be @ C2 pin22 on a 2000 buick century. I'm only getting 9volts. Is this sufficient to tell the PCM to ground C2 pin 39 to ground to energize the relay coil to send voltage to the ac compressor clutch? Any input greatly appreciated.
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ulycyc

Well-known member
542
272
63
Long Island, New York
Buick Ownership
1987 Turbo Buick, 2001 Park Ave Ultra
Code p1546 will/may set if the clutch doesn't activate from low freon or whatever. Could be a old code set when you were servicing the system. I'm not sure if the voltage should be a low reference voltage or a full 12 volts. I believe you scanner should be able to do a full hvac and component test. I hate to tell people to start probing pcm's and cause bigger issues.
Not for your car but the basic procedure is the same.
 
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