My 2000 xc is still having engine temp problems with the a/c on. I drove on the freeway yesterday for 40-50 miles with the ac on and it was fine. We pulled off the freeway and withing a few minutes the temp started to climb rather quickly. I just got in from doing some looking around under the hood. The fan does come on with the ac. The compressor is coming on as well. I let it get completely up to temp in my driveway and then took it for a ride around the neighborhood. When I saw the temp starting to rise I pulled over to see if the fan was still running and indeed it was. My new question is could this be a thermostat problem? I don't think so becaue it runs at the correct temp always with the ac off. I was told to check the resistance at the engine coolant temp sensor but I do not know where that is. And also i was told what the ohm reading should be at different temps. but what do those temps mean? 68, 104, and 212 degrees. What are those temps of??

As always, any help will be appreciated.

Ken
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2000 V70 XC / 2001 S60 totalled while parked :(

The Engine coolant temp(ECT) sensor is directly below the thermostat housing. A little hard to see, except that it has a 2 wire plug going to it.
When verifing the ohms resistance, you need to know the approximate coolant temperatures, 68F, 104F, and 212F the engine has. Because the resistance is a straight line curve, 2800 for 68F and 1200 for 104F, and 150 at 212F, it should be easy to deduce if the reading you get across the 2 wires is within bounds.
From what you have already explained, I doubt the ECT sensor is a problem.

You may have a sticky thermostat which is not opening all of the way (most Volvos fail in the open position), you may not have an OEM thermostat (replace it), your water pump is starting to fail and not pumping hard enough, your radiator may be partially clogged, your cap on the expansion bottle may be cracked opreventing full pressure, or all of the above.

Klaus
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I still miss my 164 and my 854T. Just driving a V70R :)