check engine light help!!

I hope somebody can help me out with this. I have a 94 sentra and everytime I turn on the AC, the check engine light comes on. I ran the diagnostics on the computer and it flashed 5 long and 5 short (which accourding to my trusty Haynes manual, means nothing is wrong). After I run the diagnostic, the light goes out. It will stay out until I turn on the AC. I have tested this by going two days without running the AC, then turning it on. The check engine light comes on everytime. Anybody know what's goin' on? Any help would be appreciated.

tighten your belts

tighten your belts

I checked this and they were tight, but I went the extra mile and replaced them. I've only had the car for a little under a month and it's my first import (and the newest car I've owned-most of my cars are from the 60's and 70's). The check engine light is still coming on. It doesn't matter if I'm sitting in the driveway or going 65 down the highway, everytime I turn on the AC, the check engine light comes on!
Any other suggestions? Thanks!

hmmm, got me there, tried running the diagnostic with the car running and AC on?

hmmm, got me there, tried running the diagnostic with the car running and AC on?

No, I haven't tried that but I will and get back to you. Thanks.

It worked!! The ECU is now telling me I need a new EGR, so I'm off to the parts store. Hopefully this will solve my problem. Is it normal for the EGR only to act up with the AC on? Anyway, THANK YOU so much.

that was going to be my next guess, the same belt that drives your ac drives your exhaust gas recirculator, so if your unit is bad it will prolly crap out on you if you add any stress to the belt (i.e. having the AC on) glad i could help