FSR or AC Control Unit..?

[allysam]

I had the classic symptoms of a Final Stage Resistor failure - fan staying on after the ignition is turned off/battery draning etc. I bought a cheap (not sure if it was OEM or not) replacement FSR and with the help of several threads on forums various I was able to replace the FSR. After fitting the new FSR unit, I checked the fan and hey presto it had fixed the fault.... I then re-assembled the trim, and tried it out again. All was working fine for two minutes, but then the fan started behaving erratically again and the old symptoms reappeared. Back to removing the 50A fuse to turn the fan off. Is it possible that I just had a bad/cheap non-OEM FSR, or any thoughts on saomething else blowing the FSR unit...?? Any thoughts gratefully received.