When driving my 1991 toyota corolla in rainy weather, the engine sounds loud and rough.

do you use your AC when it's raining with windows up vs not raining with windows down?

I think I know what Andrew is getting at...and I agree, tell us that...when you turn on the de-fogger, as you are likely to do when it's raining, the air is passed through the a/c condenser to remove moisture, so even if ambient temp is cold, your a/c compressor will be running

correction: it's not really a condenser, a condenser is where the gas is compressed, it's the device where the refrigerant EXPANDS, therefor cooling, and the name of it escapes me

No, I don't have the AC on. Just the fan to blow air.

That's what I mean though, you don't have to turn the a/c on, it comes on automatically whenever you blow air on the windshield to help remove moisture.

Evaporator is the word David is looking for.

The only reason I'm saying this is becasue the AC idle up feature on my car doesnt work and when i have the AC on it boggs my engine down and runs rough. Until if fix it i'm just gonna have to leave my foot on the gas while at an idle. Most cars turn the AC on automatically for AC functions and the defroster (the selection that blows on your windshield). It does this becasue the AC system not only cools air but dries it too.

Thank You Andrew, I just could not think of the word. I'm not trying to turn this in to a blog/conversation, page that's not what should go on here, but wanted to acknowledge that. @ spietro: please see what Andrew and I both are trying to explain: any time you blow air on the windshield the a/c will be on without you turning it on. The cold condenses the moist air and collects it there to drain, so the blower is putting out dry air, be it cold or warm/ fan only