I am having a problem with my 91 240 wagon with the temperature gauge spiking close to the red zone. The temp guage normally sits at the 9 o'clock position but will spike up when the ac unit has been on for awhile with the engine at idle. Once I run the car at speed, while keeping the ac on, the needle settles down to the normal position. I have checked alot of the postings and have not run into anyone with this kind of problem. I have to rule out a problem with the temp compensation board because the gauge does respond to the reaction of driving the car to cool down the engine. I have replaced the thermostat (wahler). The spike will not occur when the ac is off. The accessory cooling fan in front of the radiator does operate when the temp spikes but to no avail. I flushed the system a few months back and install new antifreeze with the correct ratio. I am lost on this one. Any suggestions??