acetaylor

So I'm driving last week and this pops up and the a/c compressor shuts off. The coolant gauge is a tick below 80C. Coolant level is fine. Drive another mile and the temperature comes up and the a/c compressor starts again and all is normal for another mile till it cools off to slightly below 80C. I assume the thermostat is bad and replace it. Fill it with distilled water (might as well flush and fill the coolant while its out) drive around the block and temperature is normal, a/c is normal, all good. Drain the water, and do another distilled water flush and I'm back to square one. Same dash symbol and no a/c.. It's hot today, in the mid 90's F.

Anyone have any ideas?

Bob C
Perkasie, PA

acetaylor

I forgot to add, this is a 07 C280 with M272 engine no check engine or any other lamps are lit.

VVF

Just random ideas - sounds like it's cooling the radiator "too effectively" I believe the normal coolant operating temperature is around 90 something.
When you turn the AC on, the big *** radiator fan switches on. Seems like the car senses that the AC -> radiator fan on -> coolant temp drop are related, and turns off the AC to get back to operating temp... ?!

Plain water has a higher specific heat capacity than coolant mix, but you tried with essentially 3 different "mixes", so that's not it.

Maybe the AC is low on refrigerant, so the condenser does not heat up as much as it's "supposed to".

acetaylor

I've spent some time reading up and researching this. Something I should have done first. In the manual that indication is for overheat or inoperative fan. I cannot make the fan run with the a/c or by heating up the engine by running the engine while parked. When it cools down I'm going to pull the fan and test it before I throw any more parts at it.