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Q: Air conditioning clutch is not engaging unless I bypass the relay.

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Before I started having this issue my A/C would take a while to get cold and in stop and go traffic would barely keep it cool. When driving on the highway 60+ mph it cooled much faster. I have cleaned the condenser with coil cleaner and had the A/C serviced. The lines have been vacuumed and also have been recharged. The pressure gauges read 210-225 on high side and 40-45 on the low side. The vehicle has rear A/C and calls for 2 1/4 lbs of r134a so I charged it with 36oz = 2 1/4 lbs. A few weeks ago I noticed the A/C clutch not engaging so I bypassed the relay and it turned right on, when I removed the bypass and replaced the relay it stayed engaged as long as car was running. If I turn the car off it would need to bypassed again to engage. All the pressure levels are maintaining so there are no leaks and it's not low on freon. My guess is the A/C pressure switch but I thought I would ask.

My car has 70000 miles.
My car has an automatic transmission.

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