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AC compressor won't cycle Topic is solved

Help, Advice and DIY Tutorials on Volvo's extremely popular car line -- Volvo's 1990s "bread and butter" cars -- powered by the ubiquitous and durable Volvo inline 5-cylinder engine.

1992 - 1997 850, 850 R, 850 T5-R, 850 T5, 850 GLT
1997 - 2000 S70, S70 AWD
1997 - 2000 V70, V70 AWD
1997 - 2000 V70-XC
1997 - 2004 C70

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Clemens
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Clemens

AC compressor won't cycle

Post by Clemens » Wed Aug 07, 2019 3:08 pm

So this is not one of these typical low on freon issues.
I had my AC refilled this spring and it actually works like a charm ( I did the zip tie fix a few years ago). I noticed something today that I can't explain:

it was raining outside, chilly 70 degree night. the AC was cycling on and off, like 10 seconds on, then off for a few, then on. I was sitting in traffic with no stereo on so I could hear it (I guess the AC bearing is starting to be a bit noisy). Then, when arriving at home in order to see if the AC charge was still good I turned the AC control to cold (if it is empty, it will cycle on/off with the temperature control on cold, otherwise it will stay on all the time). The compressor kept engaged for 2 minutes or so while I checked the AT fluid level. Then I turned the temperature controls up to 25 degree celsius (almost all the way to hot) and waited for the compressor to start cycling again. but it didn't. it just kept the compressor fully engaged until i turned the AC off.

What is happening? is the gap too narrow because of the zip tie fix and as soon as the clutch stays engaged for a while without a break it overheats and won't disengage?


Summer: 1996 855 R
Winter: 1994 855 T5M
Donor: 1995 854 10V

Ozark Lee
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Re: AC compressor won't cycle  Topic is solved

Post by Ozark Lee » Wed Aug 07, 2019 5:14 pm

If you happened to have the control set to defrost the compressor will run regardless of the temperature. A quick test to see if the gap is stuck shut is to unplug the low pressure switch (pressostat) back by the firewall. That kills the power to the compressor and it should stop running unless it is mechanically stuck on.

...Lee
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Clemens


'94 850 N/A 5 speed
'96 Platinum Edition Turbo
Previous:
1999 V70XC - Nautic Blue - Totaled while parked.
1999 V70XC - RIP - Wrecked Parts Car.
1998 S70 T5
1996 850 N/A
1989 740 GLT
1986 740 GLT
1972 142 Grand Luxe

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Re: AC compressor won't cycle

Post by jimmy57 » Thu Aug 08, 2019 12:54 pm

Idling slows compressor and the cycling occurs when the low side pressure falls to 1.85-1.9 Bar. If the compressor pumping is low then the low side may only get as low as 2.1-2.3 Bar and the pressure switch never opens and tuns off clutch. High humidity and fan speed being at half or more adds to the low side pressure making cycling while idling less likely
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