A/C compressor clutch not engaging?

Tiny
JOE1953
  • MEMBER
  • 1998 CHEVROLET MONTE CARLO
  • 3.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 127,000 MILES
I checked the freon and it show 0 on my gauge so I put 12oz of freon in and I start the engine and the compressor clutch start back working the needle on the gauge went up to like 53 or 60 PSI and the compressor clutch stop engaging again so then I connect a jumper wire from the compressor to the battery and the compressor clutch start working again when I last check the pressure on the gauge it show around 25 PSI is the freon still low? Why will it not engage on its own? What all I need to check? At 75°F outside. The vent inside the vehicle air is like 19°F, I hope you can understand it because I am trying to explain it the best I know how.
Wednesday, July 2nd, 2025 AT 9:30 PM

19 Replies

Tiny
STEVE W.
  • MECHANIC
  • 14,726 POSTS
With zero pressure you have a leak someplace, the first step would be to locate and repair the leak, then pull a vacuum on the system and see if it holds. That would test the leak repair and pull any air or moisture out of the system. Leaks go both ways once the pressure is gone. Now that the leak is repaired and you have a vacuum tested system you can charge it properly. That system holds 1.88 pounds or 22.5 ounces of R134A.

https://www.2carpros.com/articles/re-charge-an-air-conditioner-system
https://www.2carpros.com/articles/air-conditioner-leak-detection
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Thursday, July 3rd, 2025 AT 2:22 AM
Tiny
JOE1953
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How do I check for power at the compressor wires?
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Monday, July 7th, 2025 AT 4:33 PM
Tiny
STEVE W.
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You could substitute a test light, One is ground and the other is power that is controlled by the AC system. Power comes from AC fuse 10 through the clutch relay and to the clutch. A simple way to test it would be to go to that relay and jump from terminal 30 to terminal 87
If the clutch engages the wiring for it is OK. I suspect the issue is not the compressor or the wiring. The compressor only engages when there are certain items that work. The system has to have a full charge, that triggers the low pressure switch to closed. That sends power to the high pressure switch which should be closed. That then tells the ECM and BCM that the system it can engage the compressor if the control head has the AC on.
You had zero pressure which means a leak, you put in about half the charge. As soon as the compressor engages, the pressure drops and the compressor shuts off.
Your initial test shows the compressor and wiring works, it also shows that the low 134A charge is one problem. However the loss of all the 134A in the first place means there is a large leak. In the system and charging it will be a waste of money because it will simply leak out. So repair the leak. Then pull a vacuum and recharge and the system should work again.
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Monday, July 7th, 2025 AT 5:30 PM
Tiny
JOE1953
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Explain what you mean about pull a vacuum because I need to find the leak. I jump the relay but the clutch didn't engage. I can run a wire from the battery to the compressor and the clutch will engage. What make the clutch to engage? I did find a leak at the high port shrader valve with soapy water.
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Wednesday, July 9th, 2025 AT 3:37 PM
Tiny
STEVE W.
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Because the pressure was at zero that shows a leak, r134a will expand in a system and show some pressure if even a small amount were left in the system. Zero means it is empty. The seals and o-rings are designed to hold the pressure when the system is charged, when it is empty you can have the leak work like an open hole and air can get into the system. Air caries moisture. That can cause the desiccant in the drier to get moist. Water in the system is a very bad thing. So to remove the moisture and verify that the system is sealed you connect a vacuum pump as the article shows and allow it to run a while. The vacuum will vaporize the moisture and pull it out. Then you block off the vacuum and wait. If the system stays at the same vacuum level for 30 minutes you have no leaks. Then you charge the system and, if everything works, you will have AC.
To find the leak you normally use a sniffer or you can use any "dry" gas like CO2 or nitrogen, you would add that into the system and then use soapy water or bubble spray to look for the leak. The vacuum is after that is all done.
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Wednesday, July 9th, 2025 AT 4:02 PM
Tiny
JOE1953
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Can you send me pictures of the tools I need to find the leak include the vaccum pump? I looked around the compressor it was wet under the bottom of it but I didn't see no leak around the lines go to the compressor. Where are the seals and o-ring located in the compressor?
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Wednesday, July 9th, 2025 AT 6:52 PM
Tiny
STEVE W.
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That is a common failure on that compressor type, There is a sea, that opens enough to leak. If it feels oily that is likely the leak. You would need to replace the compressor, they are not repairable. That one at least isn't that bad. Remove the fan on that side, remove the belt. Unbolt the compressor and the mounts. Remove the lines from the rear of the compressor. Unbolt the mounts and the compressor. Swap the mounts to the new one, install the new O-Rings on the fittings, reverse the process to install the new one. Be sure to follow the instructions that come with the replacement. Then try the full vacuum and hold test. The guides I posted earlier show many of the tools. Plus there are videos and more showing the process on the site.
https://www.2carpros.com/articles/replace-air-conditioner-compressor
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Thursday, July 10th, 2025 AT 2:47 AM
Tiny
JOE1953
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What does a vaccum pump look like?
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Thursday, July 10th, 2025 AT 7:20 AM
Tiny
STEVE W.
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Most are a variation on this. Many parts stores have them as loaner tools.
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Thursday, July 10th, 2025 AT 7:31 AM
Tiny
JOE1953
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What all I need to replace with the Compressor or do I just replace the compressor only?
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Monday, July 14th, 2025 AT 7:28 AM
Tiny
STEVE W.
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As the compressor is only leaking you can replace just the compressor. If it had failed internally then you would be replacing more parts because of debris. However, check the warranty requirements of the actual part supplier, some will not honor the warranty unless you replace all the parts like you would for compressor failure. You will also want a seal kit, most don't come with those and while you have it apart you can replace the O-rings in the lines just to ensure they are OK. Pay close attention to the oil requirement in the instructions that will come with the compressor. They usually come prefilled and you set them clutch down for a while so the oil can coat the front seal. Others will tell you to drain both old and new and add back the same amount in the new one as came out of the old one. OH and when you recharge it, use R134A that has dye in it. That way if it leaks in the future it will be easier to find.
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Monday, July 14th, 2025 AT 8:44 AM
Tiny
JOE1953
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The compressor want be under warranty unless I replace all the parts. You said I would need s seal kit and what other parts?
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Monday, July 14th, 2025 AT 9:33 PM
Tiny
STEVE W.
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That depends on where you got it from. Most will list which pieces that have to be replaced along with the compressor. The common ones are a full system flush, orifice tube, drier, condenser core and seals. Like this kit 9611756A GPD. Then Four Seasons has the 1045NK kit which has the pieces they want replaced to keep the warranty on the new part. Pretty much the same but without the core.
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Monday, July 14th, 2025 AT 11:38 PM
Tiny
JOE1953
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I am replacing the A/C Compressor and the A/C Accumulator this is what came in the box 2 o-ring for the A/C Accumulator, 2 o-ring for the A/C Compressor and A/C Orifice tube what is the a/c orifie tube use for? How much pag oil do I add to the a/c cpmpressor. I'm not sure the compressor is prefilled wil oil. I notice the 2 new o-ring for the a/c accumulator is not as thick as the old o-ring.
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Thursday, July 17th, 2025 AT 6:06 AM
Tiny
STEVE W.
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They usually come filled and plugged. Where did you get it? Asking because adding excess oil can make a big problem. The complete system holds 9 ounces, Now as you are replacing the compressor and the accumulator and if the compressor is empty you can add 3oz to the compressor. Then add 4 more to the high side line so it can be pushed through the system. DO NOT put it on the suction side.
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Thursday, July 17th, 2025 AT 12:49 PM
Tiny
JOE1953
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I got the parts from advance auto parts how can I check to see do it have oil in it?
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Thursday, July 17th, 2025 AT 4:44 PM
Tiny
STEVE W.
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It will either come with a bottle of PAG or it will be inside the compressor held in with the plugs in the ports. Pull them out and see if you tip it around if you get 3oz or so out of it. If it was the 1045K kit it should include the oil in the kit.
The orifice tube is actually the part that makes the system work. It restricts the refrigerant flow and has a small nozzle that sprays the R134A into the line so that the liquid has more surface area to absorb more heat. Sort of like a garden hose nozzle set to a heavy mist.
If you want the same service info that shops use, you can buy a subscription for a single vehicle from alldata or mitchell. Both have DIY sections and if you wanted you can print to pdf all the sections in there for later reference.
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Friday, July 18th, 2025 AT 5:16 AM
Tiny
JOE1953
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I pull the plug out and tip the compressor a couple of drops came out is that a bad sign? On the back of the compressor it have a letter D and S what it stand for?
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Friday, July 18th, 2025 AT 6:33 PM
Tiny
STEVE W.
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That sounds like they drained it. That means you would add 3oz to the compressor, then rotate it a few times with the plugs in and then set it on the pulley so the oil can get to the seal. Leave it that way for a few minutes prior to install. D&S are the old names of the ports. Drain and Suction. Basically they are the Out and In or High and Low ports. However in your application the lines are pre-formed and can only go on one way. If I were using that compressor on something that didn't have AC and were building it all the names matter then.
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Saturday, July 19th, 2025 AT 6:07 AM

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