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AC clutch engages, but only for a second...

james_markof on Wed May 01, 2013 7:41 PM User is offline

Year: 2005
Make: Chevy
Model: Cobalt
Engine Size: 2.0
Refrigerant Type: R134a
Country of Origin: United States

My 05 cobalt is blowing hot air. I checked the ac compressor while having ac ON and noticed that it engages the clutch but only for a split second and then turns off. After about 10-15 seconds it does the same thing - start spinning for just a split sec and shuts off.

My thought was it's probably low on refrigerant, so I added this:

Yet the problem continues. I hooked up the pressure gauge to the low port and observed while the clutch was doing its thing (engaging and quickly disengaging), and saw that when the clutch kicks on for a split sec, the pressure drops, but not significantly, when the clutch is OFF, the pressure slowly builds up. Not sure if this last piece of info is helpful. With the car running and the AC clutch off, the pressure reads about 60.

The fuse is good, I replaced it. The compressor seems to be working, I just can't figure out what makes it kick OFF so soon once it kicks ON.

Also, when I replaced the fuse, it started working great. It kicked On and stayed on for about 30 minutes and then went back to doing what I described above.

Does anyone have any advice?


AutoCool on Thu May 02, 2013 4:51 AM User is offline

Check the clutch gap, it may be engaging (but slipping) then heats up quickly and that will increase the gap so it can't hold. Then disengages due to the increased gap, cools off after a while and then engages again only to heat up again and disengage Not always apparent that a clutch is slipping unless you have a strobelight or something. Magnet coil could also be weak especially if it's been overheated.

Somebody here can tell you what the LP cutoff pressure is on your system, maybe your suction pressure is dropping enough to shut off. The DIY gauges aren't exactly known for their accuracy.

james_markof on Thu May 02, 2013 3:26 PM User is offline

Is adjusting that gap a matter of tightening up any screws? Or is more involved? I don't plan to mess with it at this point, but I'm just curious.

Dougflas on Thu May 02, 2013 6:38 PM User is offline

Don't start chasing your tail. recover the charge and recharge the proper amount and start from there. A great amount of short cycling is due to improper charge.

james_markof on Fri May 03, 2013 4:33 AM User is offline

Can I ask to clarify this statement: recover the charge and recharge the proper amount and start from there
Not sure what charge you're talking about.


james_markof on Fri May 03, 2013 4:54 AM User is offline

I have read up on the clutch gap problem that AutoControl has pointed to, and the problem sure seems fit the the symptoms. I mean, if the car has set idle for a while and cooled off, the clutch will start working fine, then will start doing the same thing. The reason being, of course, is cold metal has lower resistance. So I will take it to a shop and ask them to look at that specific problem.

Dougflas on Fri May 03, 2013 5:35 AM User is offline

Originally posted by: james_markof
Can I ask to clarify this statement: recover the charge and recharge the proper amount and start from there

Not sure what charge you're talking about.


You added freon. Now you do not know how much is in the system. Use recovery equipment to capture all the freon in the system and replace it with the proper amopunt. Now you'll know that the refrigerant level is correct.

NickD on Fri May 03, 2013 7:45 AM User is offline

Believe the Cobalt uses the V-5 variable displacement compressor that should run all the time when the AC switch and blower is on. Really the only thing to shut if off is the high side thermistor. If this thermistor resistance is too high, like it would be say at a 30*F ambient, compressor won't switch on at all. Of if too low due to high temperatures caused by an excessively high side pressure, will then also shut off.

These are not easy compressors to charge by pressures due to the variable displacement nature of these compressor that vary considerably with the evaporator load and ambient conditions. Also the variable displacement control valve can be sticking that appears to be a common problem. Adding refrigerant assuming its low can be very damaging to the system. Only correct way is to recover to learn what is in there, could even be correct then put it back in. Can also be thermistor problems. And with blowing hot air, can even be blend door problems.

Clutch gap is not rocket science, just grab a feeler gauge and measure it, should be in the 20-30 mil range. Neither is the clutch coil, disconnect the vehicle connector and apply 12 V to it with an ammeter in series. Should read between 3-4 amps, remember what it reads, and let it cook for about 15 minutes, the current should decrease as the coil heat up. If it has shorted turns in the coil, that current will skyrocket telling you the coil is shot.

With all these charging kits easily available, even with sealer added and only a very inaccurate low side gauge that should be taken off the market, misleads many people to believe their refrigerant is low, a very stupid assumption. Surprised more of these systems haven't blown up in the user's face. But at least telling you that thermistor is working, or maybe even over working.

mk378 on Fri May 03, 2013 7:47 PM User is offline

Do the condenser fan(s) start? You can get an almost immediate shutdown due to overpressure if the fans don't work. Really you'd need to be able to measure the high side pressure to tell what's going on.

And like the others said, variable compressor systems must be charged by weight, or you will be chasing your tail guessing whether it is an improper charge amount or some other problem.

iceman2555 on Sat May 04, 2013 10:58 AM User is offlineView users profile

The first step for evaluating a system problem such as this is to know if the system is properly charged. The system should be recovered/evacuated/and recharged to the correct charge rate utilizing the correct equipment. Adding or subtracting refrigerant will not produce the correct conditions.
This is a CVC compressor and is a non cycling compressor. Nick is correct in his statement. The air gap could be the problem...but is not a known common issue. Have the system charged properly, evaluate the engine cooling system, fans/condenser/rad etc for proper operation and cooling performance. It appears that the HI Pressure switch is causing the system to shut down a part of the protection devices built into the system. Could be a defective switch but the other items need to be checked first. Also this system utilizes a inlet filter screen in the liquid line. This could be partially restricted and this could cause the HI pressure problem While the system is discharged remove and replace this item.
Adding the AZ Miracle in a Can is not a good choice. Now the amount of refrigerant in the system is completely unknown and this must be rectified prior to other test procedures.
This problem will, more that likely, require the services of a 'pro' and considering the post would probably be money well spend. Locate a reputable repair shop, not just one that wants to replace parts until something works, but a shop that knows how to diagnosis a problem and make the necessary repairs. Simply throwing parts at this will not produce a satisfactory result.
Good luck

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

WyrTwister on Sun May 12, 2013 10:45 AM User is offlineView users profile

I seem to remember a figure of around .030" for the clutch gap ? If this is accurate , it can be measured with a feeler gauge . A low tech and inexpensive tool .

God bless

Edited: Sun May 12, 2013 at 10:47 AM by WyrTwister

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