The A/C blower pulls switched power through the ignition switch. This is a lot of current. When the ignition switch gets old it builds up a bit of resistance, and pulling this much current though it can drop several volts on the switched side of the wiring.
A way to fix this is to wire in a relay for the blower. I modified the fusebox on my S4 to use an open relay slot and wired that up for blower power. Now the ignition switch triggers the relay, and the blower fan gets unswitched power from the fusebox. This solves the voltage drop issue.
See the thread below, particularly post #28, 49, & 51 where I explain how I did it. You've got an S3, not an S4, so it will require a different procedure but the idea is the same.
Hello All, I have a 1991 Spider Veloce, with AC. I have had this "issue" since I bought the car and it comes up every Summer on those hot days. I looked for other threads, but couldnt find what I was looking for. My AC blows cold, just not hard. When at a stand still (least amount of air...
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