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Air conditioning issues Topic is solved

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Re: Air conditioning issues  Topic is solved

Post by - Pete - » Thu Sep 05, 2019 10:19 am

Also, not positive, but I think Jimmy57 meant to put this here.
jimmy57 wrote:
Wed Sep 04, 2019 9:04 pm
if the clutch was an issue then the pressures on a 100F day would be 110 +/- on both gauges. If the heat removal fails due to blocked condenser air path or fan that quits then the high side goes WAY up and low side goes up some and then th ECM will cut off the compressor. The compressor stops but the gap has nothing to do with it. When you check or charge YOU MUST raie engine speed to 1200 or a little more. To not do that would be equivalent to checking how well the transmission shifts with engine only idling. Not my idea, it is the standard test conditions for all makes. SOme newer vehicles will have variable displacement compressors and would do so-so at idle but on any P2 except 3.2 6 cyl and V8 XC90s the compressor is not this type. The test condition with VD compressor is still elevated engine speed. If it quits cooling and you were never going below 35 mph then it is not fan related. That would be blocked condenser air path or possibly bad expansion valve. If the poor cooling starts with it idling or going below 20 mph then be sure the fn is still running. If the high side pressure gets to 275 and the fan is not cranked up to full jet sounding speed then there is a problem. The high side pressure will need to be read in the ECM parameters with a scan tool. The pressure there will likely be in kPa (100 kPa=14.7 psi) or bar (1 bar=14.7 psi) and you need to see if gauge pressure and scan tool pressure converted to psi are very close


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Re: Air conditioning issues

Post by Katten » Thu Sep 05, 2019 10:26 am

June wrote:
Thu Sep 05, 2019 8:08 am
Katten wrote:
Thu Sep 05, 2019 7:07 am
What does the gap have to do with preussare? If the gap is too large on the magnetic clutch it will not engage at any preasure :). If gap is correct it will only engage at correct preasure.
Your thinking is either it's on or off, black or white when there is a in between gray area.

Think of a standard transmission clutch that's wearing and beginning to slip. It's the same principle. The compressor clutch wears a bit at a time. The higher the pressure in the liquid line, the more resistance on the clutch ie more engine horsepower required to turn the compressor. Therefore a worn clutch may not slip with a high side reading of 175, but completely slip at 300. Once it starts slipping, the clutch will burn up fast.

The OP stated the high side was running 300-375. A worn/ slipping clutch would not stay engaged at a idle to achieve a reading that high. June
Thanks for enlighten me, it was more than I knew. Not sure I follow the logic tho :(. I might have thought abit black n white. Is there some switch that will turn the compressor off if preasure is too high?



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Re: Air conditioning issues

Post by abscate » Thu Sep 05, 2019 10:37 am

With high pressure the compressor works harder and heats up more. Hot compressor means clutch failure, the same way most compressor gap problems occur after 15 minutes of driving then are cured on cold startup


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Re: Air conditioning issues

Post by June » Thu Sep 05, 2019 7:07 pm

Katten wrote:
Thu Sep 05, 2019 10:26 am
June wrote:
Thu Sep 05, 2019 8:08 am
Katten wrote:
Thu Sep 05, 2019 7:07 am
What does the gap have to do with preussare? If the gap is too large on the magnetic clutch it will not engage at any preasure :). If gap is correct it will only engage at correct preasure.
Your thinking is either it's on or off, black or white when there is a in between gray area.

Think of a standard transmission clutch that's wearing and beginning to slip. It's the same principle. The compressor clutch wears a bit at a time. The higher the pressure in the liquid line, the more resistance on the clutch ie more engine horsepower required to turn the compressor. Therefore a worn clutch may not slip with a high side reading of 175, but completely slip at 300. Once it starts slipping, the clutch will burn up fast.

The OP stated the high side was running 300-375. A worn/ slipping clutch would not stay engaged at a idle to achieve a reading that high. June
Thanks for enlighten me, it was more than I knew. Not sure I follow the logic tho :(. I might have thought abit black n white. Is there some switch that will turn the compressor off if preasure is too high?

Yes the system will have a high pressure switch or pressure relief valve to protect the system from damage. The manufacturer sets the maximum and minimum pressure permissible by the system. It will be different from car to car depending on type of system and refrigerant used.

Think of the clutch as what connects the compressor to the engine. Maby a better analogy perhaps would be think of your car's breaks. A slipping a/c clutch is like someone riding the breaks down a mountain. Eventually the break pad material gets hot enough that they quit working. Once cooled they work again. The a/c clutch has material that grips when engaged. Quickly when the clutch is slipping slightly due to excess gap, the friction heats the material up causing slippage until it can no longer keep the compressor engaged. Once cooled the process happens again like with the driver riding and overheating breaks. I hope that makes more sense. June


My Volvo cars owned
1989 740 GLT ordered
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