AC compressor cycling every 7 secs but still cold

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Oz_850GLE
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Year and Model: Volvo 850 GLE 1994
Location: Sydney

AC compressor cycling every 7 secs but still cold

Postby Oz_850GLE » Mon Jan 31, 2011 11:50 pm

I have an 94 850 GLE Australian spec Volvo, that has had one previous owner with full meticulous service history.

The a/c in the car seems to be working fine, it blows cold, but when the car is idling the compressor clicks on and off every 5-7 seconds. When driving the car for a long period in high temp weather (100degF or 38degC) the a/c works for a while but intermittently starts blowing warm for a minute or so before going cold again.

I'm quite familiar with a/c systems having replaced a full system on a BMW 325 incl the evap.

Where should I start looking

Thanks

Steve
Sydney, Australia

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JRL
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Re: AC compressor cycling every 7 secs but still cold

Postby JRL » Mon Jan 31, 2011 11:52 pm

It may seem cold but it's either low on freon but most probably the compressor CLUTCH is failing (common)
Search how to shim it here in the repair database.
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jblackburn
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Re: AC compressor cycling every 7 secs but still cold

Postby jblackburn » Mon Jan 31, 2011 11:56 pm

You may have both of the above issues. Pick up a can of R-134a at an auto parts store, and fill the system according to the ambient temperature and the pressures indicated on the back of the can.

The clutch gap may be what's causing it to drop out when it gets too hot outside.
http://volvospeed.com/vs_forum/topic/80 ... h-gap-fix/

(You will need a Volvospeed account in order to see the picture at the bottom of that post).
'98 S70 T5
2012 Chevy Cruze LT 6MT


A learning experience is one of those things that says, "You know that thing you just did? Don't do that."

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precopster
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Re: AC compressor cycling every 7 secs but still cold

Postby precopster » Tue Feb 01, 2011 12:03 am

My wife's 850 has the same issue, it is original with factory refrigerant still inside. What have you tried so far?

The overpressure switch located near the firewall controls over & under pressure. These often go out of tolerance, so if the switch believes there is more pressure than it's higher limit allows it will cut out. You can test this by running a volt meter to the non-powered side of the switch and seeing if the voltage drops to zero when the compressor switches off.

Unfortunately refrigerant sales ( R134a) are restricted to those with a refrigeration mechanic's license in Australia since the late eighties.

Best to replace this first before a regas as it is almost impossible to swap one out while the system is pressurised due to the seal blowing out. FCP Groton stock these at around $30.
Current cars: 2000 V70NA, 2001 V70XC, 2002 XC70, 2001 V70 T5, 2006 XC90 2.5T

What we used to own:1995 850 sedan, 1987 740 sedan, 2002 S60AWD, 1989 740 turbo wagon, 1985 760 V6, 1995 850 wagon, 1999 V70 project car, 1998 V70R AWD.
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misha
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Re: AC compressor cycling every 7 secs but still cold

Postby misha » Tue Feb 01, 2011 2:08 am

Isn't that normal for ac compressor to cycle every few seconds when engine is idling(in these cars with electronic ac)? :shock:

When i bought my car it was almost new and ac compressor did that from beginning.

When it is low on freon it cycles more frequently or no cycling at all and no more cold air.

It is simple...no freon=no pressure in the system=no cold air.

I know that because i had to refill freon on mine 2 years ago after 12 years...car is '97.I needed to refill ac because compressor was cycling every second or two and there was no more cold air from vents.

After refilling i went for a leak check after a week of driving and everything was ok...no leaks,and ac compressor still cycle in about few seconds when engine is idling.Ac works like a charm.
'97 850 2.5 20v /fully equipped/ Motronic 4.4 / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic/petrol+LPG
History of Volvos in the family:
'71 144 De luxe
'73 144 De luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS

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precopster
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Re: AC compressor cycling every 7 secs but still cold

Postby precopster » Tue Feb 01, 2011 6:58 am

OK but is it normal for the A/C to go warm for up to one minute & then cool down again??

Me thinks not.
Current cars: 2000 V70NA, 2001 V70XC, 2002 XC70, 2001 V70 T5, 2006 XC90 2.5T

What we used to own:1995 850 sedan, 1987 740 sedan, 2002 S60AWD, 1989 740 turbo wagon, 1985 760 V6, 1995 850 wagon, 1999 V70 project car, 1998 V70R AWD.
Please call me Mike

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jblackburn
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Re: AC compressor cycling every 7 secs but still cold

Postby jblackburn » Tue Feb 01, 2011 1:42 pm

Nope. Look at the clutch gap fix for that issue - when they get real warm, the clutch no longer makes contact with the compressor wheel.

On a hot day, when it's holding a proper charge, my S70's compressor stays engaged about 95% of the time at idle. It may click out for a few seconds after running for up to a minute. On cooler days, it will cycle in and out more frequently to keep the evaporator from freezing up. At higher RPM (puttering along at 2000 where you can still hear it), it will also cycle in and out.
'98 S70 T5
2012 Chevy Cruze LT 6MT


A learning experience is one of those things that says, "You know that thing you just did? Don't do that."

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misha
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Re: AC compressor cycling every 7 secs but still cold

Postby misha » Thu Feb 03, 2011 7:59 pm

precopster wrote:OK but is it normal for the A/C to go warm for up to one minute & then cool down again??

Me thinks not.


Since you still have factory freon in ac compressor i think that it is just low on freon.

Maybe it's a bad ac clutch,like jablackburn said...but i think it's just low on freon.
'97 850 2.5 20v /fully equipped/ Motronic 4.4 / polar white wagon
'91 Citroen XM 2.0 SI /fully equipped/mandarine red metallic/petrol+LPG
History of Volvos in the family:
'71 144 De luxe
'73 144 De luxe
'78 244 DL
'78 244 DL
'79 244 GLE
'85 340 GLS

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cn90
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Re: AC compressor cycling every 7 secs but still cold

Postby cn90 » Thu Apr 04, 2013 4:58 pm

I think "misha" is right.

My 1998 S70 with ECC seems to do the same thing (cycling every 7 sec).
Air from center vent is cold.
So I hooked up my gauge with engine running and AC "On".
- When Clutch is off (compressor not running), pressure climbs to about 37 psi, then clutch kicks in.
- With Clutch engaged, the pressure drops from 37 psi to about 22 psi, when the Clutch is disengaged.
- The system is off for about 7 sec, during that time, the pressure builds up to 37 psi and the cycle starts again.
- In other words, this on-off cycle is about 14 sec, or about 4x/minute.

- Thinking the system is low on R134a (I might have been wrong), I added 1 can (12 oz) at a time and measured the pressures. After a total of 2 cans (24 oz total), I stopped as it did not make a big difference in pressure readings and before I blew up the system lol.

Anyway, I am back to square one with the system cycling about 4x/minute. Interior Vent drop is about 20F: outside air was 60F, center vent was 40F.

I am giving up on this, maybe it was designed from the factory this way.

PS: I will do the AC Clutch shim with zip ties later.
1998 S70 GLT 160K+
2005 XC90 2.5T 85K+

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precopster
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Re: AC compressor cycling every 7 secs but still cold

Postby precopster » Thu Apr 04, 2013 8:36 pm

My 2000 model's a/c held pressure (got to as low as 25psi) with a hole in the evaporator. The a/c would cycle about every 6 -8 seconds.

After replacing the evaporator and having the gases proffessionally evacuated and refilled pressures can be seen through Vida as 450kpa with compressor off and 1400kpa with compressor on. That's a lot higher than 50psi even when the compressor is off. I don't know which point in the a/c system provides feedback to the ECU.

My guess is that any system cycling the compressor often is low on pressure.
Current cars: 2000 V70NA, 2001 V70XC, 2002 XC70, 2001 V70 T5, 2006 XC90 2.5T

What we used to own:1995 850 sedan, 1987 740 sedan, 2002 S60AWD, 1989 740 turbo wagon, 1985 760 V6, 1995 850 wagon, 1999 V70 project car, 1998 V70R AWD.
Please call me Mike


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