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AC compressor won't engage

befuddled on Tue July 29, 2008 9:19 PM User is offline

Year: 2000
Make: Nissan
Model: Maxima
Engine Size: V6
Refrigerant Type: R134a
Ambient Temp: 75
Pressure Low: 45
Pressure High: 225
Country of Origin: United States

The compressor clutch will not engage. No problem with it when you jump the relay, it works real well then. In addition to the above readings, the vent temp is 48 degrees. The 10amp 'air cond' fuse in the dash is ok. Swapping relays proved that the relay is not the problem. I cannot find any sort of a pressure switch anywhere in the system. But the engine compartment is really crowded. The drier is down under the left headlight, a bear to get at. The pressure line runs along the left side of the motor and across the firewall, disappearing from sight many times.

In the relay socket, there is 12 volts to only one connection. No voltage at any of the other three connections under any key on/off/engine running/engine off/ac on/ac off condition. The AC control on the dash does everything it is asked to do. The temperature settings adjust, the fan blows in all speeds, then vents change upon command.

My feeling is that there is some switch in the plumbing somewhere. Any ideas?

Thank you for your help.

Chick on Tue July 29, 2008 9:44 PM User is offlineView users profile

sounds like the ECM is not sending the ground to the relay, may have to reset the computer, and that depends on the original problem

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

CyFi on Tue July 29, 2008 11:41 PM User is offline

The relay isnt getting a 12v + to the control circuit either it sounds. There should be 12v at two points in the relay harness, one to power the relay and one to power the clutch

TRB on Wed July 30, 2008 12:17 AM User is offlineView users profile

Agree with Chick, looking at the wring diagram. Power flows from the control head to the ECM. Then to the Pressure switch back through the ECM. ECM out to the compressor relay which has one leg always hot. Relay out to the compressor clutch.

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befuddled on Wed July 30, 2008 1:15 AM User is offline

CyFi, my thoughts exactly, seems like there should be two +12v for the relay. But I have been fooled before.

Chick, makes sense, but TRB, you say there is a presure switch. Any idea where? The pressure switch could be interrupting the signal. Jumping it would tell for sure, and I would have done that if I could have found it. I did not crawl underneath though. Tommorrow for that. I would expect it to be in the vicinity of the dryer.

FWIW, the original problem was a failed bearing in the clutch hub assembly. The innards of the compressor were clean as a whistle. I changed the whole unit because I could not find a replacement clutch. And I could not swap the clutch only from the replacement, my first wish, because the mounting diameters were different. The swap was unremarkable, and after I jumped the relay, the recharge was also unremarkable. The original coil was pretty beat up. It stands to reason it would blow a fuse. But, no blown fuses were found. I think the only one I found only controlled the control panel on the dash anyway.

I appreciate the help.

Think out loud for a moment, I wonder if the absense of a second 12v at the relay is because of a damaged wire there due to the original clutch coil burning out. I would think that would occur on the power side of the relay, and not the signal side.

TRB on Wed July 30, 2008 1:52 AM User is offlineView users profile

Refrigerant pressure sensor (On liquid tank).

As for the relay Brown/Red trips the relay from the ECM. Light Green is always hot. Yellow/Black to Pink/Black trips the clutch.

The program that contains this information cost my company $ 200.00 a month and the data is copyright protected. Alldata has this information for about $ 25.00 dollars per vehicle or you could try the library. Information I have listed is just whats under the hood, minus ECM. There are a few things on the inside of the vehicle also if you do not have power leaving the ECM.

Also you just list Maxima. There are 3 versions of this vehicle I'm looking at the GLE. But they wiring should the the same on all models.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Chick on Wed July 30, 2008 7:49 AM User is offlineView users profile

Did you pull a DEEP vacuum and charge into the vacuum? That should be enough to start the compressor. If you're trying to start it empty, it won't work, Needs refrigerant pressure for the ecm to send ground to the relay..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

befuddled on Wed July 30, 2008 8:42 AM User is offline

Thank you TRB, I will check that out. It scares me that the hot terminal I fed to the clutch may have been the signal supply. If the burned out clutch did damage some of the supply wire, or blow a fuse I haven't found, it may have been behind the other terminal of the relay that is supposed to be hot. I was wondering how you had a wire diagram. It is expensive to be in the AC business. I do not suppose it says which relay terminal number the various wires go to. They are hard to see from the top. Instead of two terminals always being energized, and the ECM supplying a ground, I suppose that one terminal could be permanently grounded, and the ECM supplies a +12v.

Chick, yes to the vacuum. I used a brand x 6cfm pump that rates itself at 20 microns. No micron gage, but it pulled down instantly, then I left it running for about an hour and a half. Pegged the gage. I normally would not have left it so long, but I was doing other things. I was concerned that the pump might be too big, and the initial vacuum might have been applied too fast, but it pulled from both the high and low sides, so I do not think there was any imbalance, and the system had no 134 in it. The specs call for 23 ounces(.65kg, or 22.928 ounces). I put in a 12 ounce can with dye and almost all of a second 12 oz can. I think I am slightly over the 23 oz, but there is a tolerance and I think I am within it. Better an ounce long than an ounce short?

The car has 187,000 miles on it. It will see a crusher soon, I am sure. But it runs well and is intact, and is a one owner, widowed female family member with not enough resources to replace it.

Thanks for your help.

mk378 on Wed July 30, 2008 10:14 AM User is offline

Is it the coil or the contact that is not getting power? There probably is another fuse for the clutch power to the relay.

befuddled on Wed July 30, 2008 10:23 AM User is offline

I think you are right, mk378. But it is not between the relay and the clutch. I have not yet found it if it exists. It was dark last night when I quit. Back to it soon.

TRB on Wed July 30, 2008 10:58 AM User is offlineView users profile

Email me a fax number and I fax over the wiring diagram. So you get the correct one I need to know the model and if it has manual or automatic a/c? I normally do not provide this data. But all do it this one time.

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When considering your next auto A/C purchase, please consider the site that supports you: ACkits.com
Contact: ACKits.com

Chick on Wed July 30, 2008 11:22 AM User is offlineView users profile

If it pulled down instantly, it may have just vacuumed the lines.. Be sure you vacuumed the system..Just depress a valve core and see if it pulls air in..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

befuddled on Wed July 30, 2008 11:57 AM User is offline

R E S O L V E D

Boy, am I dumb.

There is a fuse block right in plain sight beside the battery. The 10amp 'air con' fuse was blown.

I do not know if the problem was working late, tired, in the dark, or just plain too much old guy.

Chick, I never thought of that. But the pressures varied in the normal manner when recharging, so I am confident I did not make that mistake this time. Thanks to you, I will be aware of the potential next time.

TRB, thank you for your generous offer. No need now. And thank you for this forum.

Now, off to the brakes and exhaust.

Chick on Wed July 30, 2008 12:00 PM User is offlineView users profile

alls well that ends well... I'm sure you'll be aware of a lot of things next time...Glad we could help..

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Chick
Email: Chick

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Freedoms just another word for nothing left to lose

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