Why would your temp gauge go up and down to the point of almost overheating especially when the AC is on in a 2000 Olds Intrigue?

Answer 1

This answer really applies to any vehicle. The A/C puts an incredible load on the engine. If you have a problem with your cooling system, it has a hard time recooperating when the A/C is on. Your A/C clutch turns on and off several times while you are driving, it does this by using a sensor on the low side (and in some cases the high side), typically it is called a pressure cycling switch. It does this automatically (assuming it's working ok, which it sounds like yours is). When your compressor comes on, your engine receives a load, and also with the condensor (usually right in front of the radiator, it looks like a radiator) on the front of the car trying to expell heat, it is harder for the cooling system to keep the engine cool, so it heats up. When your pressure drops on the low side of your A/C (this is normal) and your compressor clutch disengages (shuts off) there is less load on the engine, and as such is easier to cool. That explains the normal fluctuations you might see in temperature. If you are seeing rapid or extreme changes, which it sounds like you are, I would recommend delving into your cooling system. Start with your electric fans behind the radiator, the way they function, is that they should come on when your car is warmed up, to regulate temperature (obviously), however, they should also come on anytime your A/C is turned on, regardless of engine temperature. This is to anticipate the increased load and heat from the engine, and to immediately get air moving across the condensor, which is a vital part to the A/C system anyway. What I'm saying, is turn your A/C on, check your fan(s) If you have two and only one is spinning, I would suspect the non-functioning fan, as typically they both will spin when the A/C is on, you might be able to jumper wires to test the non-functioning fan. If the fans aren't working, then that is probably your problem, check your fans, relays, fuses, etc. If the fan(s) are functioning properly with the A/C on, turn your car off, let it cool, and check your coolant level in your radiator, if that is ok, you may have a sticking thermostat, or other restriction in your cooling system. A faulty water pump could also create a problem. If you only see overheating (or near overheating for that matter) when your A/C is on, It is, in my opinion, most likely an issue with your fan(s). Good Luck, Scott C. The Shade Tree Technician LLC / Wichita, KS