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Car air conditioner problem

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Amusei

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I've got an old 98 Saturn SL1, which runs surprisingly well for its age. About a month ago I ran into an issue with my air conditioner and have no idea what the problem is. If the AC is on and I'm stopped, the engine overheats, and fast, it cools once I turn off the AC (30 seconds of being stopped with AC on takes ~20min to cool), but it seems picky:

Car stopped + AC on = FAST overheating and service engine light is off
Car moving + AC on = no overheating and service engine light is off
Car stopped + AC off = no overheating and service engine light is on
Car moving + AC off = no overheating and service engine light is on

The gear I'm in doesn't seem to matter and when the AC is on there's a pretty annoying rattle coming from the middle of the dash.


Can someone tell me whats wrong and how to fix it? Would be much appreciated, and if your answer is "replace it" I still want to know what the issue is.
 
Replace the engine coolant sensor that turns on the electric fans. On a GM car, when you turn the AC on, the computer tells the fans to come on. If the AC is off, then the coolant sensor tells the fan to come on as needed. It is probably not sending the correct signal to the computer.
 
^agreed. The fan isn't coming on, if you have the plastic ECTS you might need to replace the connector as well, the plastic sensors were known to crack and corrode the contacts on the harness. Now that the Saturn dealerships are defunct I'm not sure where you get these parts, supposedly GM dealerships support Saturn parts. Otherwise a junk yard will probably save you time and money, all s-series use the same sensor.

ECTS and the IAT are the same sensor as far as I know, they're interchangeable, you might try swapping the sensors and see if the overheating goes away.

Edit:
The reason your car overheats with the AC on is because in addition to the load from the AC pump the AC condenser sits in front of the radiator so cool air entering the front of the vehicle is pre-heated by the condenser making it less efficient for cooling the radiator. When the vehicle is moving air flows past the condenser and radiator fast enough that the effect is negligible, when the vehicle is stopped the condenser heats the air a lot more because the air isn't moving as fast if at all, which makes the radiator that much less efficient. The fan normally comes on when the AC is turned on so that there is always airflow across the condenser and radiator which keeps the engine temperatures down.
 
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Search the Saturnfans database for backup on these responses. There is tons of info over there.

It does sound like the ECTS. When you say check engine light, do you mean the WRENCH light? or the Service Engine Soon light?
 
For a friend's Saturn SL1 we wired in a switch to a relay that let him control when the fans turned on or off
 
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