Replaced coolant tank about a week ago, flushed coolant entirely. When I placed the new tank into position, I flushed system and added new coolant. Drove around for about 30 minutes to ensure job was done properly, no issues. Not until maybe 3 days later the a'c would cut in and out blowing cold air than hot air. That's when I noticed the engine would start to overheat. Tried purging the air out of the system by letting the engine run with expansion tank cap off and the heat on full. The coolant would than start to bubble in tank then shoot out of tank. Any suggestions on why the coolant shouts out so abruptly? My guess was there's just that much air trapped in the system? Any suggestions I would greatly appreciate! Thank you! 2009 Volvo C30R

 

I don't recommend that you let the car idle with the cap off to bleed air. I've had better luck shutting it off for a while then add coolant as it drops. It sounds to me like you never purged the air from the system.

With the limited information that you are providing, this is the best that I can do.

 

It sounds to me like your belts are slipping. When you turn on the A/C the belt slips (but not all the time). The water pump and the compressor just stop turning because the belt is slipping. This is not common, but it fits they symptoms. On older cars with old V-belts it happened all the time. Could one of your belt tensioners be bad? Broken spring so it isn't keeping the belt tight? Maybe the water pump is failing and seizing? How else is the A/C and engine temp related? Thermo fan malfunction?

As for idling with the lid off the catch tank, I would expect that exact thing. With no pressure on the system, the water will boil and spew out in pulses.

 

Unless there is something that I missed, an older C30 cars used the timing belt driven water pumps.

 

Yeah.....your right. I have too many cars.

I wonder if the car's software shuts the A/C off when the car is overheating? Never had to test that theory. Then it could be just a need to burp the engine.