I own a 1999 S70 and my AC is acting funny. It starts and stops cooling while driving. When it stops cooling, I can rev the engine to around 5,000 rpm's and it will sometimes start cooling again. I carried it to Auto Zone and the pulled a code and told me that one of my pressure switches was bad. Where could this pressure switch be located? will I have to de-pressurize my ac system to replace it? It's arctic inside my car when it is on, but feels like hell when it's not. I have checked my freon level, and it is ok. Thanks for your help.

It is probably the high pressure switch. And no, the system does not have to be emptied to replace it. The high pressure switch is behind the right side headlight.
The low pressure switch is close to the firewall, but if you have cold air that is not the problem part.


Klaus
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(V♂LV♂s 1995 854T, 1998 V70R)

Sounds like freezing and thawing to me. It freezes so there's an obstruction and no air gets in. the heat of your reving engine thaws it enough to get it running again. Why this happens, I'm not sure. Others will chime in I'm sure. Don't think you're going to have to purge the system to fix it.
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.

Well, when the air quits blowing cold, the clutch on the compressor isn't engaged. The clutch engages when I rev the engine. I was thinking that the switch is going bad and isn't reading the correct pressure, therefore when I rev the engine, it creates more pressure and allows the clutch to engage.

I was thinking it was a switch because of the codes the guy at Auto Zone pulled. One of the codes said something about my low pressure switch. I wanted to ask on here before purchasing one to see what you guys thought it could be.

Low pressure switch is up against the firewall, you can short this one to see if it is opperating. The high pressure switch is a pressure transmitter( pressure switch linear), three wire, it feeds a signal, 5V, back to the ECU, do not short this one. I replaced one of these and you do not have to purge the system. I also had to re seat the ECU befor the clutch would engage. This one is located behind the passenger side headlight.
Al

Thanks! I shorted the low pressure switch and now the compressor stays on like it should. I will try to make it to the dealer to get a replacement switch by the weekend or early next week. It looks like I will lose all of my freon when I unscrew the low pressure switch from the line, but if you all say that I will not lose any, then I guess you are more knowledgable on these cars than me. Thanks a bunch for all of your help on this matter.

Don't keep it jumpered for a long time. The system is suppose to cycle on and off and you'll end up ruining your compressor if it's on all the time. Sounds like you have an intermittant shorting issue with that switch from the descriptions I've read. The switch should take care of everything. Good luck!
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1998 S70 T5 Emarald Green Metallic, 2004 V70 2.5T Ruby Red, Previous Owner of Black '94 850 Turbo Wagon. My cars have been running so well lately they've got me worried.