Author Topic: A/C Compressor Cycles Every Minute or So  (Read 99 times)

allenga

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A/C Compressor Cycles Every Minute or So
« on: September 15, 2018, 11:01:48 AM »
My converted 134 stock system is working great.  I noticed on the freeway I can feel the AC cycling on and off every minute or so.  I can't replicate at idle watching it with the hood up.  Just had the whole system serviced.  All new hoses, o rings, orifice tube.

Outside air temp 88.

Is this behavior normal.

Thanks!
1977 Black TA, 6.6.

Warren Seale

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Re: A/C Compressor Cycles Every Minute or So
« Reply #1 on: September 15, 2018, 12:40:24 PM »
I am assuming this is the late 70s style that doesn't use a POA valve.  The cycling is caused by a low pressure condition that is being detected by the pressure sensor on low pressure side.  You can test for this by bypassing the sensor with a short on the connector.  If it stays on then the sensor is what is causing to cycle on and off.  Make sure that the system is indeed fully charged.  If it is partially charged then a low pressure condition will result even though it appears to be cooling.  The other possibility is that the sensor is faulty.

79 T/A,WS6,403,A3
96 T/A,WS6(#1344),M6
72 442,W30,A3
96 Vette Grand Sport convertible,F45,LT4,M6
06 Vette convertible,Z51,M6

firebirdparts

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Re: A/C Compressor Cycles Every Minute or So
« Reply #2 on: September 15, 2018, 06:49:08 PM »
It is normal.  The compressor is moving 2 or 3 times the volume driving that it does at idle.  At high rpms it moves even more.  The a/c has to cut the compressor off to avoid freezing.
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allenga

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Re: A/C Compressor Cycles Every Minute or So
« Reply #3 on: September 15, 2018, 09:02:29 PM »
Thanks. I was trying to find something in the shop manual to test. Every minute seems excessive?
1977 Black TA, 6.6.

Warren Seale

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Re: A/C Compressor Cycles Every Minute or So
« Reply #4 on: September 16, 2018, 11:02:53 AM »
Thanks. I was trying to find something in the shop manual to test. Every minute seems excessive?

It shouldn't cycle if it is 90+ deg outside and the blower is on maximum.  At that temperature the low pressure side should not be low enough to cause the sensor to activate.
79 T/A,WS6,403,A3
96 T/A,WS6(#1344),M6
72 442,W30,A3
96 Vette Grand Sport convertible,F45,LT4,M6
06 Vette convertible,Z51,M6

Re: A/C Compressor Cycles Every Minute or So
« Reply #4 on: September 16, 2018, 11:02:53 AM »

allenga

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Re: A/C Compressor Cycles Every Minute or So
« Reply #5 on: September 16, 2018, 11:29:21 AM »
was 90 degrees, Norm setting, fan speed #3, 65mph.  Cycling every +/- 60 seconds
1977 Black TA, 6.6.

Re: A/C Compressor Cycles Every Minute or So
« Reply #5 on: September 16, 2018, 11:29:21 AM »
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