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Very rapid cycling, then normal and repeat

Jag987 on Tue May 12, 2015 12:19 AM User is offline

Year: 98
Make: Honda
Model: Civic
Engine Size: 1.6 CNG
Refrigerant Type: R134a
Ambient Temp: 75
Pressure Low: 30
Pressure High: 180
Country of Origin: United States

Compressor is cycling very fast, 3-4 times in about as many seconds, then stays engaged for 20-30 seconds. Low side slowly drops from about 30 to close to 10 before it cycles off. Then low side pressure builds back up and the cycle repeats. Center vent temp is 40 with the doors closed. Explained below, but this the compressor was just replaced, proper oil and refrigerant charged added (by weight), system flushed, TXV and drier replaced, vacuumed, all the good stuff. It was done right this time. I will not be able to have this car again for a few days, so I thought I would ask. Any ideas what is causing this? I think it is electrical, either the pressure switch or evap temp sensor, but it is weird and something I have never seen.

My customer replaced the compressor with a rebuilt last fall because part of the clutch fell off. The clutch broke after it had been cycling as described above for some time. When it first got to me, the high presser relief valve had blown. The customer went to replace it, but it broke off inside the compressor. The company warranted the compressor because of this and another rebuild was installed. I then vacuumed the system and recharged. It appeared to be working, but it was very cold that day, around 60 when I was done. It did not work right, a few days latter I found that the relief valve had blown again and the valve had metal shavings in it. At that point, I was allowed to replace the compressor with a new one from AMA, the TXV, Drier, flushed the system....anyway, it was done right. So after all that, it is now back to the original problem of cycling way too fast.

Thanks for the help!


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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

mk378 on Tue May 12, 2015 8:26 AM User is offline

The controls on the Civic are very simple. The condenser fan should always come on all the time the compressor is engaged. If the fan does not start, compressor will trip on high pressure and cycle on the pressure switch. The only pressure sensor is a high/low cut switch on the high side that should never open in normal operation. Normal cycling is controlled by evaporator temperature.

Jag987 on Wed May 13, 2015 12:25 AM User is offline

The condenser fan does come on and I never saw the high pressure above 200. Watching the gauges, i can bypass the pressure switch and see if it still does it. It there a timer or delay of some sort that keeps the compressor off when it does cycle due to low evap temp? I found the compressor shuts off when the evap temp is read at 39, with 40 at the vents it seems this is why it is cycling off, then having problems restarting. What about a loose ground? If it worked some of the time, it could explain what is going on. Thanks mk!

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

mk378 on Wed May 13, 2015 8:51 AM User is offline

Does this rapid cycling happen only at idle? The ECU will drop the compressor if the engine rpm goes too slow and then rapidly try it again when it speeds up. Pressing the gas pedal lightly will prevent that from happening, it should then stay engaged. If that is the case you need to look at the idle control system, I don't know if it is the same on a CNG, only seen the gasoline versions here.

There is no "time delay" in the normal cycling other than that inherent in the slow temperature change of the evaporator core. In other words the cycling rate comes directly from the temperature sensor.

Edited: Wed May 13, 2015 at 8:56 AM by mk378

Jag987 on Wed May 20, 2015 2:50 PM User is offline

Well, I finally got this car back today. Plugged in the scanner to watch the rpms and hit the magic button. It worked flawlessly for the next half hour. I'm glad I could not find anything to kick! My customer said he has not used it at all because it has not been very warm here, lots of rain, and he did not want to do any damage it it. I can't fix it if it is not broke. I'm wondering if maybe it needed to "relearn" idle. I don't know what the deal was, but it is all good now.

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

Jag987 on Wed August 19, 2015 11:20 PM User is offline

My customer contacted me today. Apparently it is back to rapid cycling and has been for a long time, but he just now contacted me. It will be a few days, maybe next week before I see this car. Just wondering if anyone has any other ideas besides the pressure switch or low idle.

Thanks!
Jag

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

bohica2xo on Thu August 20, 2015 10:33 AM User is offline

Have you replaced the pressure switch? I had a bad cycling switch drive me nuts once.

.

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"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

ice-n-tropics on Thu August 27, 2015 8:01 PM User is offline

Bohica ('Yote skinner) has a good idea
Also investigate the thermal protection switch (TPS) mounted near the discharge port in the compressor housing which opens at high temp associated w/ low charge at med/high rpm, e.g., high discharge temp
remans often fail to properly install the TPS and dent the bottom can housing which results in premature cycling
Also, in cold climates if H2O leaks thru the special silicon thermal RTV mounting sealant (formally available from Honda for field recalls) ice forms and dents the bottom of the can and causes the bi metal switch to premature cycle
Hope this helps
hotrodac

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

Edited: Thu August 27, 2015 at 8:02 PM by ice-n-tropics

Jag987 on Thu August 27, 2015 8:35 PM User is offline

I still have not seen the car again, but he did call and say it is only doing it at idle. I have found on another forum that this is not a totally uncommon problem, but getting to the idle air screw is hard without some special screwdriver. Thanks for the ideas, I will post back if i ever get the car again.

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I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

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